ENH: stringOps::findTrim helper

- finds beg/end indices of string trimmed of leading/trailing whitespace

applications/test/string2/Test-string2.C

@@ -2,8 +2,10 @@
   =========                 |
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     |
-    \\  /    A nd           | Copyright (C) 2019 OpenCFD Ltd.
+    \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2019 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -93,6 +95,30 @@ void testNumericEvaluation(const std::string& s)
 }
 
 
+// Test findTrim - uses '<' and '>' as pseudo-placeholders
+void testFindTrim(const std::string& s)
+{
+    auto pos = s.find('<');
+    auto len = s.find('>');
+
+    // Conform with expected value for substr
+
+    if (pos == std::string::npos) pos = 0; else ++pos;
+    if (len != std::string::npos) len = (len - pos);
+
+    const auto pts = stringOps::findTrim(s, pos, len);
+
+    Info<< "input" << nl
+        << "========" << nl
+        << s << nl
+        << "pos=" << pos << " len=" << int(len) << nl
+        << s.substr(pos, len) << nl
+        << "trim=" << pts.first << " to " << pts.second << nl
+        << s.substr(pts.first, pts.second-pts.first) << nl
+        << "========" << nl;
+}
+
+
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 // Main program:
 
@@ -150,6 +176,28 @@ int main(int argc, char *argv[])
     }
 
 
+    // Test findTrim - uses '<' and '>' as pseudo-placeholders
+    {
+        Info<< nl << "Test findTrim" << nl;
+
+        for
+        (
+            const auto& cstr
+          :
+            {
+                "",     // Empty
+                "   \n\t   ",   // whitespace only
+                "   Leading and trailing   ",
+                "   Alt end and trai>ling   ",
+                "   Alt start<   space      ",
+            }
+        )
+        {
+            testFindTrim(cstr);
+        }
+    }
+
+
     Info<< "\nEnd\n" << endl;
     return 0;
 }

src/OpenFOAM/primitives/strings/stringOps/stringOps.C

@@ -947,15 +947,17 @@ Foam::string Foam::stringOps::trimLeft(const std::string& s)
 {
     if (!s.empty())
     {
-        std::string::size_type beg = 0;
+        std::string::size_type pos = 0;
-        while (beg < s.size() && std::isspace(s[beg]))
+        const auto end = s.length();
+
+        while (pos < end && std::isspace(s[pos]))
         {
-            ++beg;
+            ++pos;
         }
 
-        if (beg)
+        if (pos)
         {
-            return s.substr(beg);
+            return s.substr(pos);
         }
     }
 
@@ -967,15 +969,17 @@ void Foam::stringOps::inplaceTrimLeft(std::string& s)
 {
     if (!s.empty())
     {
-        std::string::size_type beg = 0;
+        std::string::size_type pos = 0;
-        while (beg < s.size() && std::isspace(s[beg]))
+        const auto end = s.length();
+
+        while (pos < end && std::isspace(s[pos]))
         {
-            ++beg;
+            ++pos;
         }
 
-        if (beg)
+        if (pos)
         {
-            s.erase(0, beg);
+            s.erase(0, pos);
         }
     }
 }
@@ -985,15 +989,15 @@ Foam::string Foam::stringOps::trimRight(const std::string& s)
 {
     if (!s.empty())
     {
-        auto n = s.size();
+        auto end = s.length();
-        while (n && std::isspace(s[n-1]))
+        while (end && std::isspace(s[end-1]))
         {
-            --n;
+            --end;
         }
 
-        if (n < s.size())
+        if (end < s.length())
         {
-            return s.substr(0, n);
+            return s.substr(0, end);
         }
     }
 
@@ -1005,35 +1009,74 @@ void Foam::stringOps::inplaceTrimRight(std::string& s)
 {
     if (!s.empty())
     {
-        auto n = s.size();
+        auto end = s.length();
-        while (n && std::isspace(s[n-1]))
+        while (end && std::isspace(s[end-1]))
         {
-            --n;
+            --end;
         }
 
-        s.resize(n);
+        s.erase(end);
     }
 }
 
 
+std::pair<std::size_t, std::size_t>
+Foam::stringOps::findTrim
+(
+    const std::string& s,
+    std::size_t pos,
+    std::size_t len
+)
+{
+    size_t end = s.length();
+    if (pos >= end)
+    {
+        pos = end;
+    }
+    else if (len != std::string::npos)
+    {
+        len += pos;
+
+        if (len < end)
+        {
+            end = len;
+        }
+    }
+
+    // Right = last
+    while (pos < end && std::isspace(s[end-1]))
+    {
+        --end;
+    }
+
+    // Left = first
+    while (pos < end && std::isspace(s[pos]))
+    {
+        ++pos;
+    }
+
+    return std::pair<std::size_t, std::size_t>(pos, end);
+}
+
+
 Foam::string Foam::stringOps::trim(const std::string& str)
 {
-    std::string::size_type beg = 0;
+    std::string::size_type pos = 0;
-    std::string::size_type end = str.size();
+    std::string::size_type end = str.length();
 
     // Right
-    while (beg < end && std::isspace(str[end-1]))
+    while (pos < end && std::isspace(str[end-1]))
     {
         --end;
     }
 
     // Left
-    while (beg < end && std::isspace(str[beg]))
+    while (pos < end && std::isspace(str[pos]))
     {
-        ++beg;
+        ++pos;
     }
 
-    return str.substr(beg, end-beg);
+    return str.substr(pos, end-pos);
 }
 
 

src/OpenFOAM/primitives/strings/stringOps/stringOps.H

@@ -36,6 +36,7 @@ SourceFiles
     stringOpsTemplates.C
 
 \*---------------------------------------------------------------------------*/
+
 #ifndef stringOps_H
 #define stringOps_H
 
@@ -48,6 +49,7 @@ SourceFiles
 #include "stringOpsSort.H"
 #include "stringOpsEvaluate.H"
 #include "wordRes.H"
+#include <utility>
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
@@ -257,6 +259,16 @@ namespace stringOps
     bool inplaceReplaceVar(std::string& s, const word& varName);
 
 
+    //- Find (first, last) non-space locations in string or sub-string.
+    //  This may change to std::string_view in the future.
+    std::pair<size_t, size_t>
+    findTrim
+    (
+        const std::string& s,
+        size_t pos = 0,
+        size_t len = std::string::npos
+    );
+
     //- Return string trimmed of leading whitespace
     string trimLeft(const std::string& s);
 

src/OpenFOAM/primitives/strings/stringOps/stringOpsEvaluate.C

@@ -42,42 +42,16 @@ Foam::string Foam::stringOps::evaluate
 {
     /// InfoErr<< "Evaluate " << str.substr(pos, len) << nl;
 
-    size_t end = str.length();
+    const auto trimPoints = stringOps::findTrim(str, pos, len);
-    if (pos > end)
-    {
-        pos = end;
-    }
-    else if (len != std::string::npos)
-    {
-        len += pos;
 
-        if (len < end)
+    pos = trimPoints.first;
-        {
+    len = (trimPoints.second - trimPoints.first);
-            end = len;
-        }
-    }
 
-    // Adjust like inplaceTrim
+    if (!len)
-
-    // Right
-    while (pos < end && std::isspace(str[end-1]))
-    {
-        --end;
-    }
-
-    // Left
-    while (pos < end && std::isspace(str[pos]))
-    {
-        ++pos;
-    }
-
-    if ((pos >= end) || std::isspace(str[pos]))
     {
         return "";
     }
 
-    len = (end - pos);
-
     /// InfoErr<< "Evaluate " << str.substr(pos, len) << nl;
 
     expressions::exprResult result;