diff --git a/applications/test/HashTable1/Make/files b/applications/test/HashTable1/Make/files
index 05c776d65c..166975418b 100644
--- a/applications/test/HashTable1/Make/files
+++ b/applications/test/HashTable1/Make/files
@@ -1,3 +1,3 @@
-Test-HashTable1.C
+Test-HashTable1.cxx
 
 EXE = $(FOAM_USER_APPBIN)/Test-HashTable1
diff --git a/applications/test/HashTable1/Test-HashTable1.C b/applications/test/HashTable1/Test-HashTable1.cxx
similarity index 100%
rename from applications/test/HashTable1/Test-HashTable1.C
rename to applications/test/HashTable1/Test-HashTable1.cxx
diff --git a/applications/test/string/Make/files b/applications/test/string/Make/files
index 2bcadc3218..7c664b3968 100644
--- a/applications/test/string/Make/files
+++ b/applications/test/string/Make/files
@@ -1,3 +1,3 @@
-Test-string.C
+Test-string.cxx
 
 EXE = $(FOAM_USER_APPBIN)/Test-string
diff --git a/applications/test/string/Test-string.C b/applications/test/string/Test-string.cxx
similarity index 98%
rename from applications/test/string/Test-string.C
rename to applications/test/string/Test-string.cxx
index 72cd2ab178..605ec9136d 100644
--- a/applications/test/string/Test-string.C
+++ b/applications/test/string/Test-string.cxx
@@ -89,7 +89,7 @@ int main(int argc, char *argv[])
 
         inputType in1("move-construct-from");
 
-        Info<<"move construct from " << in1.length() << nl;
+        Info<<"move construct from " << in1.size() << nl;
 
         outputType out1(std::move(in1));
 
@@ -100,7 +100,7 @@ int main(int argc, char *argv[])
         out1 = "some-text-rubbish";
         out1.resize(10);
 
-        Info<<"move assign from " << in1.length() << nl;
+        Info<<"move assign from " << in1.size() << nl;
 
         out1 = std::move(in1);
 
@@ -329,7 +329,7 @@ int main(int argc, char *argv[])
 
     string s2(s.expand());
 
-    cout<< "output string with " << s2.length() << " characters\n";
+    cout<< "output string with " << s2.size() << " characters\n";
     cout<< "ostream<<  >" << s2 << "<\n";
     Info<< "Ostream<<  >" << s2 << "<\n";
     Info<< "hash:" << hex << string::hasher()(s2) << dec << endl;
diff --git a/applications/test/stringList/Make/files b/applications/test/stringList/Make/files
index bcfa35a1f0..6e4f828cd5 100644
--- a/applications/test/stringList/Make/files
+++ b/applications/test/stringList/Make/files
@@ -1,3 +1,3 @@
-Test-stringList.C
+Test-stringList.cxx
 
 EXE = $(FOAM_USER_APPBIN)/Test-stringList
diff --git a/applications/test/stringList/Test-stringList.C b/applications/test/stringList/Test-stringList.cxx
similarity index 100%
rename from applications/test/stringList/Test-stringList.C
rename to applications/test/stringList/Test-stringList.cxx
diff --git a/applications/test/stringSplit/Test-stringSplit.cxx b/applications/test/stringSplit/Test-stringSplit.cxx
index 14d4cab890..638219950b 100644
--- a/applications/test/stringSplit/Test-stringSplit.cxx
+++ b/applications/test/stringSplit/Test-stringSplit.cxx
@@ -43,7 +43,7 @@ template<class StringType>
 void printSubStrings
 (
     const StringType& str,
-    const SubStrings<StringType>& split
+    const SubStrings& split
 )
 {
     Info<< "string {" << str.size() << " chars} = " << str << nl
diff --git a/applications/utilities/mesh/conversion/ensightToFoam/ensightMeshReader.C b/applications/utilities/mesh/conversion/ensightToFoam/ensightMeshReader.C
index 85de497991..e6d98f2991 100644
--- a/applications/utilities/mesh/conversion/ensightToFoam/ensightMeshReader.C
+++ b/applications/utilities/mesh/conversion/ensightToFoam/ensightMeshReader.C
@@ -645,7 +645,7 @@ bool Foam::fileFormats::ensightMeshReader::readGeometry
 
 
     // Parse all
-    SubStrings<string> split;
+    SubStrings split;
 
     while (is.good())
     {
diff --git a/applications/utilities/mesh/manipulation/objToVTK/objToVTK.C b/applications/utilities/mesh/manipulation/objToVTK/objToVTK.C
index 4ff92cf77a..4d83c8133e 100644
--- a/applications/utilities/mesh/manipulation/objToVTK/objToVTK.C
+++ b/applications/utilities/mesh/manipulation/objToVTK/objToVTK.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2015 OpenFOAM Foundation
-    Copyright (C) 2019-2021 OpenCFD Ltd.
+    Copyright (C) 2019-2025 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -37,7 +37,7 @@ Description
 
 #include "argList.H"
 #include "OFstream.H"
-#include "StringStream.H"
+#include "stringOps.H"
 #include "point.H"
 #include "DynamicList.H"
 
@@ -58,58 +58,49 @@ string getLine(std::ifstream& is)
 }
 
 
-// Read space-separated vertices (with optional '/' arguments)
-labelList parseVertices(const string& line)
+// Token list with one of the following:
+//     f v1 v2 v3 ...
+//     f v1/vt1 v2/vt2 v3/vt3 ...
+//     l v1 v2 v3 ...
+//     l v1/vt1 v2/vt2 v3/vt3 ...
+static label readObjVertices
+(
+    const SubStrings& tokens,
+    DynamicList<label>& verts
+)
 {
-    DynamicList<label> verts;
+    verts.clear();
 
-    // Assume 'l' is followed by space.
-    string::size_type endNum = 1;
-
-    do
+    bool first = true;
+    for (const auto& tok : tokens)
     {
-        string::size_type startNum = line.find_first_not_of(' ', endNum);
-
-        if (startNum == string::npos)
+        if (first)
         {
-            break;
+            // skip initial "f" or "l"
+            first = false;
+            continue;
         }
 
-        endNum = line.find(' ', startNum);
+        std::string vrtSpec(tok.str());
 
-        string vertexSpec;
-        if (endNum != string::npos)
+        if
+        (
+            const auto slash = vrtSpec.find('/');
+            slash != std::string::npos
+        )
         {
-            vertexSpec = line.substr(startNum, endNum-startNum);
-        }
-        else
-        {
-            vertexSpec = line.substr(startNum, line.size() - startNum);
+            vrtSpec.erase(slash);
         }
 
-        string::size_type slashPos = vertexSpec.find('/');
+        label vertId = readLabel(vrtSpec);
 
-        label vertI = 0;
-        if (slashPos != string::npos)
-        {
-            IStringStream intStream(vertexSpec.substr(0, slashPos));
-
-            intStream >> vertI;
-        }
-        else
-        {
-            IStringStream intStream(vertexSpec);
-
-            intStream >> vertI;
-        }
-        verts.append(vertI - 1);
+        verts.push_back(vertId - 1);
     }
-    while (true);
 
-    return verts.shrink();
+    return verts.size();
 }
 
-
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
 int main(int argc, char *argv[])
 {
@@ -142,6 +133,8 @@ int main(int argc, char *argv[])
     DynamicList<labelList> polyLines;
     DynamicList<labelList> polygons;
 
+    DynamicList<label> dynVerts;
+
     bool hasWarned = false;
 
     label lineNo = 0;
@@ -152,33 +145,58 @@ int main(int argc, char *argv[])
 
         if (line.empty()) continue;
 
-        // Read first word
-        IStringStream lineStream(line);
-        word cmd(lineStream);
+        const auto tokens = stringOps::splitSpace(line);
+
+        // Require command and some arguments
+        if (tokens.size() < 2)
+        {
+            continue;
+        }
+
+        const word cmd = word::validate(tokens[0]);
 
         if (cmd == "v")
         {
-            scalar x, y, z;
+            // Vertex
+            // v x y z
 
-            lineStream >> x >> y >> z;
-
-            points.append(point(x, y, z));
+            points.emplace_back
+            (
+                readScalar(tokens[1]),
+                readScalar(tokens[2]),
+                readScalar(tokens[3])
+            );
         }
         else if (cmd == "vn")
         {
-            scalar x, y, z;
+            // Vertex normals
+            // vn x y z
 
-            lineStream >> x >> y >> z;
-
-            pointNormals.append(vector(x, y, z));
+            pointNormals.emplace_back
+            (
+                readScalar(tokens[1]),
+                readScalar(tokens[2]),
+                readScalar(tokens[3])
+            );
         }
         else if (cmd == "l")
         {
-            polyLines.append(parseVertices(line));
+            // Line
+            // l v1 v2 v3 ...
+            // OR
+            // l v1/vt1 v2/vt2 v3/vt3 ...
+
+            readObjVertices(tokens, dynVerts);
+            polyLines.emplace_back() = dynVerts;
         }
         else if (cmd == "f")
         {
-            polygons.append(parseVertices(line));
+            // f v1 v2 v3 ...
+            // OR
+            // f v1/vt1 v2/vt2 v3/vt3 ...
+
+            readObjVertices(tokens, dynVerts);
+            polygons.emplace_back() = dynVerts;
         }
         else if (cmd != "")
         {
@@ -188,7 +206,7 @@ int main(int argc, char *argv[])
 
                 WarningInFunction
                     << "Unrecognized OBJ command " << cmd << nl
-                    << "In line " << lineStream.str()
+                    << "In line " << line
                     << " at linenumber " << lineNo << nl
                     << "Only recognized commands are 'v' and 'l'.\n"
                     << "If this is a surface command use surfaceConvert instead"
@@ -230,46 +248,42 @@ int main(int argc, char *argv[])
     }
 
     label nItems = 0;
-    forAll(polyLines, polyI)
+    for (const labelList& line : polyLines)
     {
-        nItems += polyLines[polyI].size() + 1;
+        nItems += line.size() + 1;
     }
 
     outFile
         << "LINES " << polyLines.size() << ' ' << nItems << nl;
 
-    forAll(polyLines, polyI)
+    for (const labelList& line : polyLines)
     {
-        const labelList& line = polyLines[polyI];
-
         outFile << line.size();
 
-        forAll(line, i)
+        for (const label vrt : line)
         {
-            outFile << ' ' << line[i];
+            outFile << ' ' << vrt;
         }
         outFile << nl;
     }
 
 
     nItems = 0;
-    forAll(polygons, polyI)
+    for (const labelList& line : polygons)
     {
-        nItems += polygons[polyI].size() + 1;
+        nItems += line.size() + 1;
     }
 
     outFile
         << "POLYGONS " << polygons.size() << ' ' << nItems << nl;
 
-    forAll(polygons, polyI)
+    for (const labelList& line : polygons)
     {
-        const labelList& line = polygons[polyI];
-
         outFile << line.size();
 
-        forAll(line, i)
+        for (const label vrt : line)
         {
-            outFile << ' ' << line[i];
+            outFile << ' ' << vrt;
         }
         outFile << nl;
     }
diff --git a/src/OSspecific/POSIX/POSIX.C b/src/OSspecific/POSIX/POSIX.C
index dffd5e0a54..a346b47b96 100644
--- a/src/OSspecific/POSIX/POSIX.C
+++ b/src/OSspecific/POSIX/POSIX.C
@@ -119,6 +119,8 @@ static inline void* loadLibrary(const Foam::fileName& libName)
     constexpr int ldflags = (RTLD_LAZY|RTLD_GLOBAL);
 
 #ifdef __APPLE__
+    using namespace Foam;
+
     const char* normal = nullptr;
     const char* shadow = nullptr;
 
@@ -132,8 +134,8 @@ static inline void* loadLibrary(const Foam::fileName& libName)
         // SIP appears to have cleared DYLD_LIBRARY_PATH but the
         // shadow parameter is available
 
-        const Foam::string ldPaths(shadow);
-        const auto paths = Foam::stringOps::split<Foam::string>(ldPaths, ':');
+        const std::string ldPaths(shadow);
+        const auto paths = Foam::stringOps::split(ldPaths, ':');
 
         for (const auto& p : paths)
         {
diff --git a/src/OpenFOAM/Make/files b/src/OpenFOAM/Make/files
index b19173cddc..5f75e7d074 100644
--- a/src/OpenFOAM/Make/files
+++ b/src/OpenFOAM/Make/files
@@ -158,14 +158,15 @@ $(strings)/keyType/keyType.C
 $(strings)/regex/regExpCxx.C
 $(strings)/wordRe/wordRe.C
 $(strings)/wordRes/wordRes.C
-$(strings)/lists/CStringList.C
-$(strings)/lists/hashedWordList.C
+$(strings)/lists/CStringList.cxx
+$(strings)/lists/hashedWordList.cxx
 $(strings)/parsing/parsing.C
 $(strings)/parsing/genericRagelLemonDriver.C
-$(strings)/stringOps/stringOps.C
-$(strings)/stringOps/stringOpsEvaluate.C
-$(strings)/stringOps/stringOpsSort.C
-$(strings)/stringOps/stringOpsSplit.C
+$(strings)/stringOps/stringOps.cxx
+$(strings)/stringOps/stringOpsEvaluate.cxx
+$(strings)/stringOps/stringOpsSort.cxx
+$(strings)/stringOps/stringOpsSplit.cxx
+$(strings)/stringOps/stringOpsSubstr.cxx
 
 expr = expressions
 $(expr)/exprEntry/expressionEntry.C
diff --git a/src/OpenFOAM/db/dictionary/dictionarySearch.C b/src/OpenFOAM/db/dictionary/dictionarySearch.C
index 35c067f0f0..ffb8c058b9 100644
--- a/src/OpenFOAM/db/dictionary/dictionarySearch.C
+++ b/src/OpenFOAM/db/dictionary/dictionarySearch.C
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2017-2023 OpenCFD Ltd.
+    Copyright (C) 2017-2025 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -192,8 +192,7 @@ Foam::dictionary::const_searcher Foam::dictionary::csearchSlashScoped
         }
     }
 
-    // Split on '/'
-    auto cmpts = stringOps::split<std::string>(keyword, '/');
+    auto cmpts = stringOps::split(keyword, '/');
     auto remaining = cmpts.size();
 
     for (const auto& cmpt : cmpts)
@@ -397,7 +396,7 @@ const Foam::dictionary* Foam::dictionary::cfindScopedDict
 
     fileName path(dictPath); // Work on copy
     path.clean();  // Remove unneeded ".."
-    auto dictCmpts = stringOps::split(path, '/');  // Split on '/'
+    auto dictCmpts = stringOps::split(path, '/');
 
     for (const auto& cmpt : dictCmpts)
     {
@@ -502,7 +501,7 @@ Foam::dictionary* Foam::dictionary::makeScopedDict(const fileName& dictPath)
 
     std::string path(dictPath); // Work on a copy
     fileName::clean(path);  // Remove unneeded ".."
-    auto dictCmpts = stringOps::split(path, '/'); // Split on '/'
+    auto dictCmpts = stringOps::split(path, '/');
 
     for (const auto& cmpt : dictCmpts)
     {
diff --git a/src/OpenFOAM/expressions/exprDriver/exprDriver.C b/src/OpenFOAM/expressions/exprDriver/exprDriver.C
index f8afebea5e..7108256ba6 100644
--- a/src/OpenFOAM/expressions/exprDriver/exprDriver.C
+++ b/src/OpenFOAM/expressions/exprDriver/exprDriver.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2010-2018 Bernhard Gschaider
-    Copyright (C) 2019-2021 OpenCFD Ltd.
+    Copyright (C) 2019-2025 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -387,8 +387,7 @@ void Foam::expressions::exprDriver::addVariables
     }
 
     // Allow inline list of semicolon-separated variables
-    const auto varExpressions =
-        stringOps::split<expressions::exprString>(expr, ';');
+    const auto varExpressions = stringOps::split(expr, ';');
 
     for (const auto& subMatch : varExpressions)
     {
diff --git a/src/OpenFOAM/expressions/exprTools/exprTools.C b/src/OpenFOAM/expressions/exprTools/exprTools.C
index ac9449529f..cc1c459f21 100644
--- a/src/OpenFOAM/expressions/exprTools/exprTools.C
+++ b/src/OpenFOAM/expressions/exprTools/exprTools.C
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2019-2022 OpenCFD Ltd.
+    Copyright (C) 2019-2025 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -59,7 +59,7 @@ static List<expressions::exprString> expandExprStrings
     for (const string& input : inputs)
     {
         // Allow inline list of semicolon-separated variables
-        const auto varExpressions = stringOps::split<string>(input, ';');
+        const auto varExpressions = stringOps::split(input, ';');
 
         for (const auto& subMatch : varExpressions)
         {
diff --git a/src/OpenFOAM/primitives/strings/fileName/fileName.C b/src/OpenFOAM/primitives/strings/fileName/fileName.C
index 0e31f8205a..86636e631f 100644
--- a/src/OpenFOAM/primitives/strings/fileName/fileName.C
+++ b/src/OpenFOAM/primitives/strings/fileName/fileName.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2016-2023 OpenCFD Ltd.
+    Copyright (C) 2016-2025 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -538,7 +538,7 @@ Foam::fileName Foam::fileName::relative
 
 Foam::wordList Foam::fileName::components(const char delim) const
 {
-    const auto parsed = stringOps::split<string>(*this, delim);
+    const auto parsed = stringOps::split(*this, delim);
 
     wordList words(parsed.size());
 
@@ -561,7 +561,7 @@ Foam::word Foam::fileName::component
     const char delim
 ) const
 {
-    const auto parsed = stringOps::split<string>(*this, delim);
+    const auto parsed = stringOps::split(*this, delim);
 
     if (parsed.size())
     {
diff --git a/src/OpenFOAM/primitives/strings/lists/CStringList.H b/src/OpenFOAM/primitives/strings/lists/CStringList.H
index ec9b173675..c4977a298d 100644
--- a/src/OpenFOAM/primitives/strings/lists/CStringList.H
+++ b/src/OpenFOAM/primitives/strings/lists/CStringList.H
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2016-2024 OpenCFD Ltd.
+    Copyright (C) 2016-2025 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -54,6 +54,7 @@ Description
 #include "fileNameList.H"
 #include "stringList.H"
 #include "wordList.H"
+#include "SubStrings.H"
 
 #include <algorithm>  // std::copy
 #include <utility>    // std::initializer_list
@@ -63,9 +64,6 @@ Description
 namespace Foam
 {
 
-// Forward Declarations
-template<class StringType> class SubStrings;
-
 /*---------------------------------------------------------------------------*\
                          Class CStringList Declaration
 \*---------------------------------------------------------------------------*/
@@ -137,8 +135,7 @@ public:
 
         //- Copy construct from a list of sub-string references
         //  Copies the input characters.
-        template<class StringType>
-        inline explicit CStringList(const SubStrings<StringType>& input);
+        explicit CStringList(const SubStrings& input);
 
 
     //- Destructor. Invokes clear() to free memory.
@@ -155,10 +152,10 @@ public:
     // Access
 
         //- True if the size (ie, argc) is zero.
-        inline bool empty() const noexcept;
+        bool empty() const noexcept { return !argc_; }
 
         //- Return the number of C-strings (ie, argc)
-        inline int size() const noexcept;
+        int size() const noexcept { return argc_; }
 
         //- The flattened character content, with interspersed nul-chars
         const char* cdata_bytes() const noexcept { return data_; }
@@ -174,11 +171,11 @@ public:
         size_t length() const noexcept { return nbytes_; }
 
         //- Return string element at the given index. No bounds checking.
-        const char* get(int i) const;
+        const char* get(int i) const { return argv_[i]; }
 
         //- Return the list of C-strings (ie, argv)
         //  The position at argc is a nullptr
-        inline char** strings() const noexcept;
+        char** strings() const noexcept { return argv_; }
 
         //- Return the sublist of C-strings (ie, argv) starting at the
         //- specified offset.
@@ -198,31 +195,36 @@ public:
         //- Copy the input list of strings.
         //  \return number of arguments (argc)
         template<class StringType>
-        inline int reset(const UList<StringType>& input);
+        int reset(const UList<StringType>& input)
+        {
+            return resetContent(input);
+        }
 
         //- Copy the input list of strings.
         //  \return number of arguments (argc)
-        template<class StringType>
-        inline int reset(const SubStrings<StringType>& input);
+        int reset(const SubStrings& input)
+        {
+            return resetContent(input);
+        }
 
 
     // Other
 
         //- Create a list from argc/argv parameters.
         //  A null pointer for argv is permissible when argc is zero.
-        template<class StringType>
+        template<class StringType = std::string>
         static List<StringType> asList(int argc, const char * const argv[]);
 
         //- Create a list from a nullptr-terminated list of argv parameters.
         //  Using a nullptr for argv is permissible.
-        template<class StringType>
+        template<class StringType = std::string>
         static inline List<StringType> asList(const char * const argv[]);
 
 
     // Member Operators
 
         //- Return element at the given index. No bounds checking.
-        inline const char* operator[](int i) const;
+        const char* operator[](int i) const { return argv_[i]; }
 };
 
 
@@ -241,7 +243,7 @@ Ostream& operator<<(Ostream& os, const CStringList& list);
 #include "CStringListI.H"
 
 #ifdef NoRepository
-#   include "CStringListTemplates.C"
+#   include "CStringList.txx"
 #endif
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
diff --git a/src/OpenFOAM/primitives/strings/lists/CStringList.C b/src/OpenFOAM/primitives/strings/lists/CStringList.cxx
similarity index 92%
rename from src/OpenFOAM/primitives/strings/lists/CStringList.C
rename to src/OpenFOAM/primitives/strings/lists/CStringList.cxx
index d9edbe829c..0eead0d803 100644
--- a/src/OpenFOAM/primitives/strings/lists/CStringList.C
+++ b/src/OpenFOAM/primitives/strings/lists/CStringList.cxx
@@ -28,8 +28,19 @@ License
 #include "CStringList.H"
 #include "Ostream.H"
 
+// * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
+
+Foam::CStringList::CStringList(const SubStrings& input)
+:
+    CStringList()
+{
+    resetContent(input);
+}
+
+
 // * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
+// Largely identical to resetContent() except with 'c-string'
 int Foam::CStringList::reset
 (
     std::initializer_list<const char* const> input
diff --git a/src/OpenFOAM/primitives/strings/lists/CStringListTemplates.C b/src/OpenFOAM/primitives/strings/lists/CStringList.txx
similarity index 97%
rename from src/OpenFOAM/primitives/strings/lists/CStringListTemplates.C
rename to src/OpenFOAM/primitives/strings/lists/CStringList.txx
index 69a1d717d2..6e4d48cc49 100644
--- a/src/OpenFOAM/primitives/strings/lists/CStringListTemplates.C
+++ b/src/OpenFOAM/primitives/strings/lists/CStringList.txx
@@ -25,8 +25,6 @@ License
 
 \*---------------------------------------------------------------------------*/
 
-#include "SubStrings.H"
-
 // * * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * //
 
 template<class ListType>
@@ -45,6 +43,7 @@ int Foam::CStringList::resetContent(const ListType& input)
     // Count overall required string length, including each trailing nul char
     for (const auto& s : input)
     {
+        // NB: use length() instead of size() to support std::sub_match
         nbytes_ += s.length() + 1;
     }
     --nbytes_;  // Do not include final nul char in overall count
diff --git a/src/OpenFOAM/primitives/strings/lists/CStringListI.H b/src/OpenFOAM/primitives/strings/lists/CStringListI.H
index 112a3791dc..87dbc7bac3 100644
--- a/src/OpenFOAM/primitives/strings/lists/CStringListI.H
+++ b/src/OpenFOAM/primitives/strings/lists/CStringListI.H
@@ -86,16 +86,7 @@ inline Foam::CStringList::CStringList(const UList<StringType>& input)
 :
     CStringList()
 {
-    reset(input);
-}
-
-
-template<class StringType>
-inline Foam::CStringList::CStringList(const SubStrings<StringType>& input)
-:
-    CStringList()
-{
-    reset(input);
+    resetContent(input);
 }
 
 
@@ -127,56 +118,10 @@ inline void Foam::CStringList::clear()
 }
 
 
-inline bool Foam::CStringList::empty() const noexcept
-{
-    return !argc_;
-}
-
-
-inline int Foam::CStringList::size() const noexcept
-{
-    return argc_;
-}
-
-
-inline char** Foam::CStringList::strings() const noexcept
-{
-    return argv_;
-}
-
-
 inline char** Foam::CStringList::strings(int start) const
 {
     return &(argv_[start]);
 }
 
 
-template<class StringType>
-inline int Foam::CStringList::reset(const UList<StringType>& input)
-{
-    return resetContent(input);
-}
-
-
-template<class StringType>
-inline int Foam::CStringList::reset(const SubStrings<StringType>& input)
-{
-    return resetContent(input);
-}
-
-
-// * * * * * * * * * * * * * * * Member Operators  * * * * * * * * * * * * * //
-
-inline const char* Foam::CStringList::get(int i) const
-{
-    return argv_[i];
-}
-
-
-inline const char* Foam::CStringList::operator[](int i) const
-{
-    return argv_[i];
-}
-
-
 // ************************************************************************* //
diff --git a/src/OpenFOAM/primitives/strings/lists/SubStrings.H b/src/OpenFOAM/primitives/strings/lists/SubStrings.H
index 4e97f6b90c..78f1496323 100644
--- a/src/OpenFOAM/primitives/strings/lists/SubStrings.H
+++ b/src/OpenFOAM/primitives/strings/lists/SubStrings.H
@@ -35,7 +35,7 @@ Description
 #ifndef Foam_SubStrings_H
 #define Foam_SubStrings_H
 
-#include <regex>    // For std::sub_match
+#include <regex>    // For std::ssub_match
 #include <memory>
 #include <string>
 #include <vector>
@@ -49,22 +49,32 @@ namespace Foam
                          Class SubStrings Declaration
 \*---------------------------------------------------------------------------*/
 
-template<class StringType>
 class SubStrings
 :
-    public std::vector<std::sub_match<typename StringType::const_iterator>>
+    public std::vector<std::ssub_match>
 {
 public:
 
-    // Types
+    // Static Functions
 
-        //- The element type
-        using value_type =
-            typename std::sub_match<typename StringType::const_iterator>;
+        #if __cplusplus >= 201703L
+        //- Return match as a string_view
+        static std::string_view view(const std::ssub_match& m)
+        {
+            if (!m.matched) return std::string_view();
 
-        //- The const_iterator for the underlying string type
-        using string_iterator =
-            typename StringType::const_iterator;
+            #if __cplusplus >= 202002L
+            return std::string_view(m.first, m.second);
+            #else
+            // No string_view construct from iterator pairs before c++20
+            return std::string_view
+            (
+                std::pointer_traits<const char*>::pointer_to(*(m.first)),
+                (m.second - m.first)
+            );
+            #endif
+        }
+        #endif  /* __cplusplus >= 201703L */
 
 
     // Member Functions
@@ -89,8 +99,8 @@ public:
             return (*this)[pos].length();
         }
 
-        //- Retrieve element at pos, converted to a string type.
-        StringType str(size_t pos) const
+        //- Retrieve element at pos, as a string
+        std::string str(size_t pos) const
         {
             return (*this)[pos].str();
         }
@@ -99,40 +109,23 @@ public:
         //- Return element at pos as a string_view
         std::string_view view(size_t pos) const
         {
-            #if __cplusplus >= 202002L
-            return std::string_view
-            (
-                (*this)[pos].first,
-                (*this)[pos].second
-            );
-            #else
-            // No string_view construct from iterator pairs before c++20
-            const auto& s = (*this)[pos];
-            return std::string_view
-            (
-                std::pointer_traits<const char*>::pointer_to(*(s.first)),
-                (s.second - s.first)
-            );
-            #endif
+            return view((*this)[pos]);
         }
         #endif  /* __cplusplus >= 201703L */
 
         //- Append sub-string defined by begin/end iterators
         void append
         (
-            const typename StringType::const_iterator& b,
-            const typename StringType::const_iterator& e
+            std::string::const_iterator b,
+            std::string::const_iterator e
         )
         {
-            value_type range;
+            auto& range = this->emplace_back();
             range.first = b;
             range.second = e;
             range.matched = true;
-
-            this->push_back(range);
         }
 
-
         //- Reduce size by 1 or more elements. Can be called on an empty list.
         void pop_back(size_t n = 1)
         {
diff --git a/src/OpenFOAM/primitives/strings/lists/hashedWordList.H b/src/OpenFOAM/primitives/strings/lists/hashedWordList.H
index fc9f5f8026..3b75788f46 100644
--- a/src/OpenFOAM/primitives/strings/lists/hashedWordList.H
+++ b/src/OpenFOAM/primitives/strings/lists/hashedWordList.H
@@ -32,8 +32,8 @@ Description
     situations than using the normal list find/found methods.
 
 SourceFiles
+    hashedWordList.cxx
     hashedWordListI.H
-    hashedWordList.C
 
 \*---------------------------------------------------------------------------*/
 
diff --git a/src/OpenFOAM/primitives/strings/lists/hashedWordList.C b/src/OpenFOAM/primitives/strings/lists/hashedWordList.cxx
similarity index 100%
rename from src/OpenFOAM/primitives/strings/lists/hashedWordList.C
rename to src/OpenFOAM/primitives/strings/lists/hashedWordList.cxx
diff --git a/src/OpenFOAM/primitives/strings/lists/stringListOps.H b/src/OpenFOAM/primitives/strings/lists/stringListOps.H
index 43d855d102..261b895c6a 100644
--- a/src/OpenFOAM/primitives/strings/lists/stringListOps.H
+++ b/src/OpenFOAM/primitives/strings/lists/stringListOps.H
@@ -37,7 +37,7 @@ Description
     Various utility functions to work on lists of strings.
 
 SourceFiles
-    stringListOpsTemplates.C
+    stringListOps.txx
 
 \*---------------------------------------------------------------------------*/
 
@@ -486,7 +486,7 @@ namespace Foam
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
 #ifdef NoRepository
-    #include "stringListOpsTemplates.C"
+    #include "stringListOps.txx"
 #endif
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
diff --git a/src/OpenFOAM/primitives/strings/lists/stringListOpsTemplates.C b/src/OpenFOAM/primitives/strings/lists/stringListOps.txx
similarity index 100%
rename from src/OpenFOAM/primitives/strings/lists/stringListOpsTemplates.C
rename to src/OpenFOAM/primitives/strings/lists/stringListOps.txx
diff --git a/src/OpenFOAM/primitives/strings/stringOps/stringOps.H b/src/OpenFOAM/primitives/strings/stringOps/stringOps.H
index 1bc9de4758..7566b3092b 100644
--- a/src/OpenFOAM/primitives/strings/stringOps/stringOps.H
+++ b/src/OpenFOAM/primitives/strings/stringOps/stringOps.H
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2012 OpenFOAM Foundation
-    Copyright (C) 2016-2024 OpenCFD Ltd.
+    Copyright (C) 2016-2025 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -31,8 +31,10 @@ Description
     Collection of static functions for various string-related operations
 
 SourceFiles
-    stringOps.C
-    stringOpsTemplates.C
+    stringOps.cxx
+    stringOps.txx
+    stringOpsSplit.cxx
+    stringOpsSubstr.cxx
 
 \*---------------------------------------------------------------------------*/
 
@@ -40,9 +42,9 @@ SourceFiles
 #define Foam_stringOps_H
 
 #include "scalar.H"
-#include "SubStrings.H"
 #include "dictionary.H"
 #include "HashTable.H"
+#include "SubStrings.H"
 #include "stringOpsSort.H"
 #include "stringOpsEvaluate.H"
 #include "word.H"
@@ -369,11 +371,10 @@ namespace stringOps
     //- Split string into sub-strings at the delimiter character.
     //  Empty sub-strings are normally suppressed.
     //  Behaviour is ill-defined if delim is a NUL character.
-    template<class StringType>
-    Foam::SubStrings<StringType> split
+    Foam::SubStrings split
     (
         //! The string to split
-        const StringType& str,
+        const std::string& str,
         //! The delimiter for splitting. Ill-defined if NUL character
         const char delim,
         //! Offset within string to start splitting
@@ -384,11 +385,10 @@ namespace stringOps
 
     //- Split string into sub-strings using delimiter string.
     //  Empty sub-strings are normally suppressed.
-    template<class StringType>
-    Foam::SubStrings<StringType> split
+    Foam::SubStrings split
     (
         //! The string to split
-        const StringType& str,
+        const std::string& str,
         //! The delimiters for splitting. Ill-defined if empty
         const std::string& delim,
         //! Offset within string to start splitting
@@ -400,11 +400,10 @@ namespace stringOps
     //- Split string into sub-strings using any characters in delimiter.
     //  Empty sub-strings are normally suppressed.
     //  Behaviour is ill-defined if delim is an empty string.
-    template<class StringType>
-    Foam::SubStrings<StringType> splitAny
+    Foam::SubStrings splitAny
     (
         //! The string to split
-        const StringType& str,
+        const std::string& str,
         //! The delimiters for splitting. Ill-defined if empty!
         const std::string& delim,
         //! Offset within string to start splitting
@@ -413,11 +412,10 @@ namespace stringOps
 
     //- Split string into sub-strings using a fixed field width.
     //  Behaviour is ill-defined if width is zero.
-    template<class StringType>
-    Foam::SubStrings<StringType> splitFixed
+    Foam::SubStrings splitFixed
     (
         //! The string to split
-        const StringType& str,
+        const std::string& str,
         //! Fixed field width for each sub-string
         const std::string::size_type width,
         //! Offset within string to start splitting
@@ -426,11 +424,10 @@ namespace stringOps
 
     //- Split string into sub-strings at whitespace (TAB, NL, VT, FF, CR, SPC)
     //  Empty sub-strings are suppressed.
-    template<class StringType>
-    Foam::SubStrings<StringType> splitSpace
+    Foam::SubStrings splitSpace
     (
         //! The string to split
-        const StringType& str,
+        const std::string& str,
         //! Offset within string to start splitting
         std::string::size_type pos = 0
     );
@@ -460,7 +457,7 @@ namespace stringOps
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
 #ifdef NoRepository
-    #include "stringOpsTemplates.C"
+    #include "stringOps.txx"
 #endif
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
diff --git a/src/OpenFOAM/primitives/strings/stringOps/stringOps.C b/src/OpenFOAM/primitives/strings/stringOps/stringOps.cxx
similarity index 99%
rename from src/OpenFOAM/primitives/strings/stringOps/stringOps.C
rename to src/OpenFOAM/primitives/strings/stringOps/stringOps.cxx
index 4ef6719911..e10e1291e0 100644
--- a/src/OpenFOAM/primitives/strings/stringOps/stringOps.C
+++ b/src/OpenFOAM/primitives/strings/stringOps/stringOps.cxx
@@ -177,7 +177,7 @@ static void expandLeadingTilde(std::string& s)
     }
     else
     {
-        s = home(user)/file;
+        s = Foam::home(user)/file;
     }
 }
 
@@ -1033,7 +1033,7 @@ Foam::stringOps::findTrim
         ++pos;
     }
 
-    return std::pair<std::size_t, std::size_t>(pos, end);
+    return {pos, end};
 }
 
 
diff --git a/src/OpenFOAM/primitives/strings/stringOps/stringOps.txx b/src/OpenFOAM/primitives/strings/stringOps/stringOps.txx
new file mode 100644
index 0000000000..7bfb23150b
--- /dev/null
+++ b/src/OpenFOAM/primitives/strings/stringOps/stringOps.txx
@@ -0,0 +1,96 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2016-2024 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+\*---------------------------------------------------------------------------*/
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+template<class StringType, class UnaryPredicate>
+StringType Foam::stringOps::quotemeta
+(
+    const StringType& str,
+    const UnaryPredicate& meta,
+    const char quote
+)
+{
+    if (str.empty() || !quote)
+    {
+        return str;
+    }
+
+    StringType result;
+    result.reserve(1.5*str.size());  // Moderately pessimistic
+
+    bool escaped = false;
+    for (const char c : str)
+    {
+        if (c == quote)
+        {
+            escaped = !escaped;  // toggle state
+        }
+        else if (escaped)
+        {
+            escaped = false;
+        }
+        else if (meta(c))
+        {
+            result += quote;
+        }
+        result += c;
+    }
+
+    result.shrink_to_fit();
+    return result;
+}
+
+
+template<class StringType, class UnaryPredicate>
+StringType Foam::stringOps::validate
+(
+    const std::string& str,
+    const UnaryPredicate& accept,
+    const bool invert
+)
+{
+    StringType out;
+    out.resize(str.length());
+
+    std::string::size_type len = 0;
+
+    for (std::string::size_type i = 0; i < str.length(); ++i)
+    {
+        const char c = str[i];
+        if (accept(c) ? !invert : invert)
+        {
+            out[len++] += c;
+        }
+    }
+
+    out.erase(len);
+    return out;
+}
+
+
+// ************************************************************************* //
diff --git a/src/OpenFOAM/primitives/strings/stringOps/stringOpsEvaluate.C b/src/OpenFOAM/primitives/strings/stringOps/stringOpsEvaluate.cxx
similarity index 100%
rename from src/OpenFOAM/primitives/strings/stringOps/stringOpsEvaluate.C
rename to src/OpenFOAM/primitives/strings/stringOps/stringOpsEvaluate.cxx
diff --git a/src/OpenFOAM/primitives/strings/stringOps/stringOpsSort.H b/src/OpenFOAM/primitives/strings/stringOps/stringOpsSort.H
index 10d2cd904e..3574b3e6b6 100644
--- a/src/OpenFOAM/primitives/strings/stringOps/stringOpsSort.H
+++ b/src/OpenFOAM/primitives/strings/stringOps/stringOpsSort.H
@@ -30,12 +30,12 @@ Description
     Specialized string sorting.
 
 SourceFiles
-    stringOpsSort.C
+    stringOpsSort.cxx
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef stringOpsSort_H
-#define stringOpsSort_H
+#ifndef Foam_stringOpsSort_H
+#define Foam_stringOpsSort_H
 
 #include "stringOps.H"
 
diff --git a/src/OpenFOAM/primitives/strings/stringOps/stringOpsSort.C b/src/OpenFOAM/primitives/strings/stringOps/stringOpsSort.cxx
similarity index 100%
rename from src/OpenFOAM/primitives/strings/stringOps/stringOpsSort.C
rename to src/OpenFOAM/primitives/strings/stringOps/stringOpsSort.cxx
diff --git a/src/OpenFOAM/primitives/strings/stringOps/stringOpsSplit.C b/src/OpenFOAM/primitives/strings/stringOps/stringOpsSplit.cxx
similarity index 96%
rename from src/OpenFOAM/primitives/strings/stringOps/stringOpsSplit.C
rename to src/OpenFOAM/primitives/strings/stringOps/stringOpsSplit.cxx
index 05de8a2d6a..098dc52341 100644
--- a/src/OpenFOAM/primitives/strings/stringOps/stringOpsSplit.C
+++ b/src/OpenFOAM/primitives/strings/stringOps/stringOpsSplit.cxx
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2016 OpenFOAM Foundation
-    Copyright (C) 2021 OpenCFD Ltd.
+    Copyright (C) 2021-2025 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -99,7 +99,7 @@ Foam::label Foam::stringOps::splitFunctionArgs
     // The depth of the argument parsing
     int argLevel = 0;
 
-    const auto strLen = str.length();
+    const auto strLen = str.size();
 
     // Pass 1: parsing begin/end parse positions.
 
@@ -136,11 +136,11 @@ Foam::label Foam::stringOps::splitFunctionArgs
                 if (isNamed)
                 {
                     named.push_back(argName);
-                    named.push_back(rangeType(beg, pos));
+                    named.emplace_back(beg, pos);
                 }
                 else
                 {
-                    unnamed.push_back(rangeType(beg, pos));
+                    unnamed.emplace_back(beg, pos);
                 }
                 isNamed = false;
                 beg = pos + 1;
diff --git a/src/OpenFOAM/primitives/strings/stringOps/stringOpsTemplates.C b/src/OpenFOAM/primitives/strings/stringOps/stringOpsSubstr.cxx
similarity index 68%
rename from src/OpenFOAM/primitives/strings/stringOps/stringOpsTemplates.C
rename to src/OpenFOAM/primitives/strings/stringOps/stringOpsSubstr.cxx
index 29b230497f..e4825f7c08 100644
--- a/src/OpenFOAM/primitives/strings/stringOps/stringOpsTemplates.C
+++ b/src/OpenFOAM/primitives/strings/stringOps/stringOpsSubstr.cxx
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2016-2024 OpenCFD Ltd.
+    Copyright (C) 2017-2025 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -25,84 +25,19 @@ License
 
 \*---------------------------------------------------------------------------*/
 
+#include "stringOps.H"
+
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
-template<class StringType, class UnaryPredicate>
-StringType Foam::stringOps::quotemeta
-(
-    const StringType& str,
-    const UnaryPredicate& meta,
-    const char quote
-)
-{
-    if (str.empty() || !quote)
-    {
-        return str;
-    }
-
-    StringType result;
-    result.reserve(1.5*str.size());  // Moderately pessimistic
-
-    bool escaped = false;
-    for (const char c : str)
-    {
-        if (c == quote)
-        {
-            escaped = !escaped;  // toggle state
-        }
-        else if (escaped)
-        {
-            escaped = false;
-        }
-        else if (meta(c))
-        {
-            result += quote;
-        }
-        result += c;
-    }
-
-    result.shrink_to_fit();
-    return result;
-}
-
-
-template<class StringType, class UnaryPredicate>
-StringType Foam::stringOps::validate
+Foam::SubStrings Foam::stringOps::split
 (
     const std::string& str,
-    const UnaryPredicate& accept,
-    const bool invert
-)
-{
-    StringType out;
-    out.resize(str.length());
-
-    std::string::size_type len = 0;
-
-    for (std::string::size_type i = 0; i < str.length(); ++i)
-    {
-        const char c = str[i];
-        if (accept(c) ? !invert : invert)
-        {
-            out[len++] += c;
-        }
-    }
-
-    out.erase(len);
-    return out;
-}
-
-
-template<class StringType>
-Foam::SubStrings<StringType> Foam::stringOps::split
-(
-    const StringType& str,
     const char delim,
     std::string::size_type pos,
     const bool keepEmpty
 )
 {
-    Foam::SubStrings<StringType> list;
+    Foam::SubStrings list;
 
     if
     (
@@ -135,16 +70,15 @@ Foam::SubStrings<StringType> Foam::stringOps::split
 }
 
 
-template<class StringType>
-Foam::SubStrings<StringType> Foam::stringOps::split
+Foam::SubStrings Foam::stringOps::split
 (
-    const StringType& str,
+    const std::string& str,
     const std::string& delim,
     std::string::size_type pos,
     const bool keepEmpty
 )
 {
-    Foam::SubStrings<StringType> list;
+    Foam::SubStrings list;
 
     if
     (
@@ -177,15 +111,14 @@ Foam::SubStrings<StringType> Foam::stringOps::split
 }
 
 
-template<class StringType>
-Foam::SubStrings<StringType> Foam::stringOps::splitAny
+Foam::SubStrings Foam::stringOps::splitAny
 (
-    const StringType& str,
+    const std::string& str,
     const std::string& delim,
     std::string::size_type pos
 )
 {
-    Foam::SubStrings<StringType> list;
+    Foam::SubStrings list;
 
     if
     (
@@ -219,15 +152,14 @@ Foam::SubStrings<StringType> Foam::stringOps::splitAny
 }
 
 
-template<class StringType>
-Foam::SubStrings<StringType> Foam::stringOps::splitFixed
+Foam::SubStrings Foam::stringOps::splitFixed
 (
-    const StringType& str,
+    const std::string& str,
     const std::string::size_type width,
     std::string::size_type pos
 )
 {
-    Foam::SubStrings<StringType> list;
+    Foam::SubStrings list;
 
     if
     (
@@ -263,10 +195,9 @@ Foam::SubStrings<StringType> Foam::stringOps::splitFixed
 }
 
 
-template<class StringType>
-Foam::SubStrings<StringType> Foam::stringOps::splitSpace
+Foam::SubStrings Foam::stringOps::splitSpace
 (
-    const StringType& str,
+    const std::string& str,
     std::string::size_type pos
 )
 {
diff --git a/src/meshTools/edgeMesh/edgeFormats/obj/OBJedgeFormat.C b/src/meshTools/edgeMesh/edgeFormats/obj/OBJedgeFormat.C
index 0c771c74e5..b184cab621 100644
--- a/src/meshTools/edgeMesh/edgeFormats/obj/OBJedgeFormat.C
+++ b/src/meshTools/edgeMesh/edgeFormats/obj/OBJedgeFormat.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2018-2022 OpenCFD Ltd.
+    Copyright (C) 2018-2025 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -44,7 +44,7 @@ namespace Foam
 //     l v1/vt1 v2/vt2 v3/vt3 ...
 static label readObjVertices
 (
-    const SubStrings<string>& tokens,
+    const SubStrings& tokens,
     DynamicList<label>& verts
 )
 {
@@ -60,17 +60,20 @@ static label readObjVertices
             continue;
         }
 
-        const string vrtSpec(tok);
-        const auto slash = vrtSpec.find('/');
+        std::string vrtSpec(tok.str());
 
-        const label vertId =
+        if
         (
-            slash != string::npos
-          ? readLabel(vrtSpec.substr(0, slash))
-          : readLabel(vrtSpec)
-        );
+            const auto slash = vrtSpec.find('/');
+            slash != std::string::npos
+        )
+        {
+            vrtSpec.erase(slash);
+        }
 
-        verts.append(vertId - 1);
+        label vertId = readLabel(vrtSpec);
+
+        verts.push_back(vertId - 1);
     }
 
     return verts.size();
diff --git a/src/surfMesh/readers/ensight/ensightSurfaceReader.C b/src/surfMesh/readers/ensight/ensightSurfaceReader.C
index 29fbc5af5c..61aaa16885 100644
--- a/src/surfMesh/readers/ensight/ensightSurfaceReader.C
+++ b/src/surfMesh/readers/ensight/ensightSurfaceReader.C
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2015-2024 OpenCFD Ltd.
+    Copyright (C) 2015-2025 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -58,10 +58,9 @@ namespace Foam
 //
 // thus call extractTimeset with minElements == 2
 //
-template<class StringType>
 static inline labelPair extractTimeset
 (
-    const SubStrings<StringType>& split,
+    const SubStrings& split,
     const std::size_t minElements
 )
 {
@@ -239,7 +238,7 @@ void Foam::ensightSurfaceReader::readCase(ISstream& is)
     }
 
     string buffer;
-    SubStrings<string> split;
+    SubStrings split;
 
     ParseSection parseState = ParseSection::UNKNOWN;
 
diff --git a/src/surfMesh/surfaceFormats/nas/NASsurfaceFormat.C b/src/surfMesh/surfaceFormats/nas/NASsurfaceFormat.C
index 0e19dbc55a..6b4e8e0310 100644
--- a/src/surfMesh/surfaceFormats/nas/NASsurfaceFormat.C
+++ b/src/surfMesh/surfaceFormats/nas/NASsurfaceFormat.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2015 OpenFOAM Foundation
-    Copyright (C) 2017-2024 OpenCFD Ltd.
+    Copyright (C) 2017-2025 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -191,8 +191,7 @@ bool Foam::fileFormats::NASsurfaceFormat<Face>::read
         if (line.starts_with("$ANSA_NAME"))
         {
             // Keep empty elements when splitting
-            const auto args =
-                stringOps::split<std::string>(line, ';', 0, true);
+            const auto args = stringOps::split(line, ';', 0, true);
 
             if (args.size() > 4 && line.starts_with("$ANSA_NAME_COMMENT"))
             {
diff --git a/src/surfMesh/surfaceFormats/obj/OBJsurfaceFormat.C b/src/surfMesh/surfaceFormats/obj/OBJsurfaceFormat.C
index 4fd5c08a5f..1383a9d070 100644
--- a/src/surfMesh/surfaceFormats/obj/OBJsurfaceFormat.C
+++ b/src/surfMesh/surfaceFormats/obj/OBJsurfaceFormat.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2016 OpenFOAM Foundation
-    Copyright (C) 2016-2022 OpenCFD Ltd.
+    Copyright (C) 2016-2025 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -168,17 +168,20 @@ bool Foam::fileFormats::OBJsurfaceFormat<Face>::read
                     continue;
                 }
 
-                const string vrtSpec(tok);
-                const auto slash = vrtSpec.find('/');
+                std::string vrtSpec(tok.str());
 
-                const label vertId =
+                if
                 (
-                    slash != string::npos
-                  ? readLabel(vrtSpec.substr(0, slash))
-                  : readLabel(vrtSpec)
-                );
+                    const auto slash = vrtSpec.find('/');
+                    slash != std::string::npos
+                )
+                {
+                    vrtSpec.erase(slash);
+                }
 
-                dynVerts.append(vertId - 1);
+                label vertId = readLabel(vrtSpec);
+
+                dynVerts.push_back(vertId - 1);
             }
 
             const labelUList& f = dynVerts;
diff --git a/src/thermophysicalModels/basic/basicThermo/basicThermo.C b/src/thermophysicalModels/basic/basicThermo/basicThermo.C
index f012c7a914..d9102cf9ab 100644
--- a/src/thermophysicalModels/basic/basicThermo/basicThermo.C
+++ b/src/thermophysicalModels/basic/basicThermo/basicThermo.C
@@ -590,7 +590,7 @@ Foam::wordList Foam::basicThermo::splitThermoName
     // Splits things like
     // "hePsiThermo<pureMixture<const<hConst<perfectGas<specie>>,enthalpy>>>"
 
-    const auto parsed = stringOps::splitAny<std::string>(thermoName, " ,<>");
+    const auto parsed = stringOps::splitAny(thermoName, " ,<>");
     const int nParsed(parsed.size());
 
     wordList cmpts;