COMP: avoid constructor ambiguity for ISpanStream

- compiler cannot decide between std::string and std::string_view
  when creating from 'const char*' without also supplying the size,
  so also supply a 'const char*' constructor.

ENH: additional string_view handling for ITstream and SubStrings

applications/test/stringSplit/Make/files

@@ -1,3 +1,3 @@
-Test-stringSplit.C
+Test-stringSplit.cxx
 
 EXE = $(FOAM_USER_APPBIN)/Test-stringSplit

applications/test/stringSplit/Test-stringSplit.cxx

@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2017-2024 OpenCFD Ltd.
+    Copyright (C) 2017-2025 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -50,11 +50,12 @@ void printSubStrings
         << split.size() << " elements {" << split.length() << " chars}"
         << nl;
 
-    unsigned i = 0;
+    for (unsigned i = 0; i < split.size(); ++i)
-    for (const auto s : split)
     {
-        Info<< "[" << i++ << "] {" << s.length() << " chars} = "
+        const auto& s = split[i];
-            << s.str() << nl;
+        Info<< "[" << i << "] {" << s.length() << " chars} = "
+            << split.view(i) << " == " << s.str()
+            << nl;
     }
 }
 

src/OpenFOAM/db/IOstreams/Tstreams/ITstream.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.
@@ -32,11 +32,6 @@ License
 #include <algorithm>
 #include <memory>
 
-// * * * * * * * * * * * * * * Static Data Members * * * * * * * * * * * * * //
-
-static std::unique_ptr<Foam::ITstream> emptyStreamPtr_;
-
-
 // * * * * * * * * * * * * * * * Local Functions * * * * * * * * * * * * * * //
 
 namespace Foam
@@ -74,20 +69,22 @@ static label parseStream(ISstream& is, tokenList& tokens)
 
 Foam::ITstream& Foam::ITstream::empty_stream()
 {
-    if (emptyStreamPtr_)
+    static std::unique_ptr<ITstream> singleton;
+
+    if (!singleton)
     {
-        emptyStreamPtr_->ITstream::clear();  // Ensure it really is empty
+        singleton = std::make_unique<ITstream>(Foam::zero{}, "empty-stream");
-        emptyStreamPtr_->ITstream::seek(0);  // rewind() bypassing virtual
     }
     else
     {
-        emptyStreamPtr_.reset(new ITstream(Foam::zero{}, "empty-stream"));
+        singleton->ITstream::clear();  // Ensure it really is empty
+        singleton->ITstream::seek(0);  // rewind() bypassing virtual
     }
 
-    // Set stream as bad to indicate that this is an invald stream
+    // Set stream as bad - indicates it is not a valid stream
-    emptyStreamPtr_->setBad();
+    singleton->setBad();
 
-    return *emptyStreamPtr_;
+    return *singleton;
 }
 
 
@@ -186,7 +183,7 @@ Foam::ITstream::ITstream
 
 Foam::ITstream::ITstream
 (
-    const Foam::zero,
+    Foam::zero,
     const string& name,
     IOstreamOption streamOpt
 )
@@ -242,19 +239,6 @@ Foam::ITstream::ITstream
 }
 
 
-Foam::ITstream::ITstream
-(
-    const std::string& input,
-    IOstreamOption streamOpt,
-    const string& name
-)
-:
-    ITstream(streamOpt, name)
-{
-    reset(input.data(), input.size());
-}
-
-
 Foam::ITstream::ITstream
 (
     const char* input,

src/OpenFOAM/db/IOstreams/Tstreams/ITstream.H

@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2016 OpenFOAM Foundation
-    Copyright (C) 2017-2024 OpenCFD Ltd.
+    Copyright (C) 2017-2025 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -122,7 +122,7 @@ public:
         //- Construct empty, optionally with given name
         explicit ITstream
         (
-            const Foam::zero,
+            Foam::zero,
             const string& name = "input",
             IOstreamOption streamOpt = IOstreamOption()
         );
@@ -152,15 +152,6 @@ public:
             const string& name = "input"
         );
 
-        //- Construct token list by parsing the input string
-        //  Uses static parse function internally.
-        explicit ITstream
-        (
-            const std::string& input,
-            IOstreamOption streamOpt = IOstreamOption(),
-            const string& name = "input"
-        );
-
         //- Construct token list by parsing the input character sequence
         //  Uses static parse function internally.
         explicit ITstream
@@ -170,20 +161,23 @@ public:
             const string& name = "input"
         );
 
-        #if __cplusplus >= 201703L
         //- Construct token list by parsing the input character sequence
         //  Uses static parse function internally.
         explicit ITstream
         (
+            #if __cplusplus >= 201703L
             std::string_view s,
-            IOstreamOption streamOpt = IOstreamOption()
+            #else
+            const std::string& s,
+            #endif
+            IOstreamOption streamOpt = IOstreamOption(),
+            const string& name = "input"
         )
         :
-            ITstream(streamOpt)
+            ITstream(streamOpt, name)
         {
             reset(s.data(), s.size());
         }
-        #endif
 
         //- Construct token list by parsing the input character sequence
         //  Uses static parse function internally.

src/OpenFOAM/db/IOstreams/memory/ISpanStream.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.
@@ -202,13 +202,28 @@ public:
             stream_type::clear();  // Clear old errors
         }
 
+        //- Reset the get buffer area to use the nul-terminated buffer
+        void reset(const char* s)
+        {
+            reset(s, (s ? std::char_traits<char>::length(s) : 0));
+        }
+
         //- Reset the get buffer area to use the data from a string
         void reset(const std::string& s)
         {
-            buffer_type::resetg(const_cast<char*>(&s[0]), s.size());
+            buffer_type::resetg(const_cast<char*>(s.data()), s.size());
             stream_type::clear();  // Clear old errors
         }
 
+        #if __cplusplus >= 201703L
+        //- Reset the get buffer area to use the data from a string_view
+        void reset(std::string_view s)
+        {
+            buffer_type::resetg(const_cast<char*>(s.data()), s.size());
+            stream_type::clear();  // Clear old errors
+        }
+        #endif
+
         //- Some information about the input buffer position/capacity
         void debug_info(Ostream& os) const
         {
@@ -257,17 +272,37 @@ public:
             reset(buffer, nbytes);
         }
 
+        //- Construct using specified nul-terminated buffer
+        explicit ISpanStream(const char* buffer)
+        :
+            ISpanStream
+            (
+                buffer,
+                (buffer ? std::char_traits<char>::length(buffer) : 0)
+            )
+        {}
+
         //- Use data area from string content
         explicit ISpanStream
         (
-            const std::string& buffer,
+            const std::string& s,
             IOstreamOption streamOpt = IOstreamOption()
         )
         :
-            ISpanStream(streamOpt)
+            ISpanStream(s.data(), s.size(), streamOpt)
-        {
+        {}
-            reset(buffer);
+
-        }
+        #if __cplusplus >= 201703L
+        //- Use data area from string_view content
+        explicit ISpanStream
+        (
+            std::string_view s,
+            IOstreamOption streamOpt = IOstreamOption()
+        )
+        :
+            ISpanStream(s.data(), s.size(), streamOpt)
+        {}
+        #endif
 
         //- Construct using data area from a List and its inherent storage size
         //  Uses addressed size, thus no special treatment for a DynamicList
@@ -280,18 +315,6 @@ public:
             ISpanStream(buffer.cdata(), buffer.size(), streamOpt)
         {}
 
-        #if __cplusplus >= 201703L
-        //- Construct (shallow copy) from std::string_view content
-        explicit ISpanStream
-        (
-            std::string_view s,
-            IOstreamOption streamOpt = IOstreamOption()
-        )
-        :
-            ISpanStream(s.data(), s.size(), streamOpt)
-        {}
-        #endif
-
         //- Construct (shallow copy) from span character content
         explicit ISpanStream
         (
@@ -357,7 +380,7 @@ public:
         //- Reset input area to use data from a string
         void reset(const std::string& s)
         {
-            stream_.reset(s);
+            stream_.reset(s.data(), s.size());
             syncState();
         }
 

src/OpenFOAM/db/IOstreams/memory/OSpanStream.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.
@@ -197,7 +197,7 @@ public:
         void reset(std::string& s)
         {
             s.resize(s.capacity());
-            buffer_type::resetp(&s[0], s.size());
+            buffer_type::resetp(s.data(), s.size());
             stream_type::clear();  // Clear any old errors
         }
 

src/OpenFOAM/primitives/strings/lists/SubStrings.H

@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2017-2024 OpenCFD Ltd.
+    Copyright (C) 2017-2025 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -36,6 +36,7 @@ Description
 #define Foam_SubStrings_H
 
 #include <regex>    // For std::sub_match
+#include <memory>
 #include <string>
 #include <vector>
 
@@ -82,12 +83,40 @@ public:
             return len;
         }
 
+        //- Return length of element at pos
+        std::string::size_type length(size_t pos) const
+        {
+            return (*this)[pos].length();
+        }
+
         //- Retrieve element at pos, converted to a string type.
         StringType str(size_t pos) const
         {
             return (*this)[pos].str();
         }
 
+        #if __cplusplus >= 201703L
+        //- 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
+        }
+        #endif  /* __cplusplus >= 201703L */
+
         //- Append sub-string defined by begin/end iterators
         void append
         (
@@ -135,16 +164,6 @@ public:
                 this->resize(this->size() - n);
             }
         }
-
-
-    // FUTURE?
-    //  #if __cplusplus >= 201703L
-    //  std::string_view view(size_t pos) const
-    //  {}
-    //  #else
-    //  stdFoam::span<const char> view(size_t pos) const
-    //  {}
-    //  #endif
 };