replace std::string::substr() with operations that do not allocate memory

Modify the original string instead of creating a new copy with substr() when it
is not used for anything else afterwards.

Source/CPack/cmCPackNSISGenerator.cxx

@@ -103,7 +103,7 @@ int cmCPackNSISGenerator::PackageFiles()
         componentName = fileN.substr(0, slash);
 
         // Strip off the component part of the path.
-        fileN = fileN.substr(slash + 1);
+        fileN.erase(0, slash + 1);
       }
     }
     std::replace(fileN.begin(), fileN.end(), '/', '\\');

Source/CPack/cpack.cxx

@@ -85,7 +85,7 @@ int cpackDefinitionArgument(const char* argument, const char* cValue,
     return 0;
   }
   std::string key = value.substr(0, pos);
-  value = value.substr(pos + 1);
+  value.erase(0, pos + 1);
   def->Map[key] = value;
   cmCPack_Log(def->Log, cmCPackLog::LOG_DEBUG,
               "Set CPack variable: " << key << " to \"" << value << "\""

Source/CTest/cmCTestGIT.cxx

@@ -6,6 +6,7 @@
 #include <cstdio>
 #include <cstdlib>
 #include <ctime>
+#include <utility>
 #include <vector>
 
 #include "cmsys/FStream.hxx"
@@ -193,7 +194,8 @@ bool cmCTestGIT::UpdateByFetchAndReset()
       if (line.find("\tnot-for-merge\t") == std::string::npos) {
         std::string::size_type pos = line.find('\t');
         if (pos != std::string::npos) {
-          sha1 = line.substr(0, pos);
+          sha1 = std::move(line);
+          sha1.resize(pos);
         }
       }
     }

Source/CTest/cmCTestScriptHandler.cxx

@@ -284,12 +284,14 @@ int cmCTestScriptHandler::ReadInScript(const std::string& total_script_arg)
   // if the argument has a , in it then it needs to be broken into the fist
   // argument (which is the script) and the second argument which will be
   // passed into the scripts as S_ARG
-  std::string script = total_script_arg;
+  std::string script;
   std::string script_arg;
   const std::string::size_type comma_pos = total_script_arg.find(',');
   if (comma_pos != std::string::npos) {
     script = total_script_arg.substr(0, comma_pos);
     script_arg = total_script_arg.substr(comma_pos + 1);
+  } else {
+    script = total_script_arg;
   }
   // make sure the file exists
   if (!cmSystemTools::FileExists(script)) {

Source/CTest/cmCTestTestHandler.cxx

@@ -1893,7 +1893,8 @@ void cmCTestTestHandler::ExpandTestsToRunInformationForRerunFailed()
         continue;
       }
 
-      int val = atoi(line.substr(0, pos).c_str());
+      line.erase(pos);
+      int val = atoi(line.c_str());
       this->TestsToRun.push_back(val);
     }
     ifs.close();
@@ -2114,7 +2115,7 @@ void cmCTestTestHandler::CleanTestOutput(std::string& output, size_t length)
       ++current;
     }
   }
-  output = output.substr(0, current - begin);
+  output.erase(current - begin);
 
   // Append truncation message.
   std::ostringstream msg;

Source/CTest/cmParseMumpsCoverage.cxx

@@ -113,7 +113,8 @@ bool cmParseMumpsCoverage::LoadPackages(std::string const& d)
   glob.FindFiles(pat);
   for (std::string& file : glob.GetFiles()) {
     std::string name = cmSystemTools::GetFilenameName(file);
-    this->RoutineToDirectory[name.substr(0, name.size() - 2)] = file;
+    name.erase(name.size() - 2);
+    this->RoutineToDirectory[name] = file;
     // initialize each file, this is left out until CDash is fixed
     // to handle large numbers of files
     this->InitializeMumpsFile(file);

Source/bindexplib.cxx

@@ -352,14 +352,14 @@ bool DumpFileWithLlvmNm(std::string const& nmPath, const char* filename,
               line.c_str());
       return false;
     }
-    const std::string sym = line.substr(0, sym_end);
     const char sym_type = line[sym_end + 1];
+    line.resize(sym_end);
     switch (sym_type) {
       case 'D':
-        dataSymbols.insert(sym);
+        dataSymbols.insert(line);
         break;
       case 'T':
-        symbols.insert(sym);
+        symbols.insert(line);
         break;
     }
   }

Source/cmCTest.cxx

@@ -725,7 +725,7 @@ bool cmCTest::UpdateCTestConfiguration()
         continue;
       }
       while (fin && (line.back() == '\\')) {
-        line = line.substr(0, line.size() - 1);
+        line.resize(line.size() - 1);
         buffer[0] = 0;
         fin.getline(buffer, 1023);
         buffer[1023] = 0;
@@ -2668,7 +2668,7 @@ std::string cmCTest::GetShortPathToFile(const char* cfname)
 
     path = "./" + *res;
     if (path.back() == '/') {
-      path = path.substr(0, path.size() - 1);
+      path.resize(path.size() - 1);
     }
   }
 

Source/cmComputeLinkInformation.cxx

@@ -1798,10 +1798,10 @@ void cmComputeLinkInformation::GetRPath(std::vector<std::string>& runtimeDirs,
       if (use_build_rpath) {
         std::string d = ri;
         if (!rootPath.empty() && cmHasPrefix(d, rootPath)) {
-          d = d.substr(rootPath.size());
+          d.erase(0, rootPath.size());
         } else if (stagePath && *stagePath && cmHasPrefix(d, stagePath)) {
-          std::string suffix = d.substr(strlen(stagePath));
+          d.erase(0, strlen(stagePath));
-          d = cmStrCat(installPrefix, '/', suffix);
+          d = cmStrCat(installPrefix, '/', d);
           cmSystemTools::ConvertToUnixSlashes(d);
         } else if (use_relative_build_rpath) {
           // If expansion of the $ORIGIN token is supported and permitted per
@@ -1829,10 +1829,10 @@ void cmComputeLinkInformation::GetRPath(std::vector<std::string>& runtimeDirs,
             !cmSystemTools::IsSubDirectory(ri, topBinaryDir)) {
           std::string d = ri;
           if (!rootPath.empty() && cmHasPrefix(d, rootPath)) {
-            d = d.substr(rootPath.size());
+            d.erase(0, rootPath.size());
           } else if (stagePath && *stagePath && cmHasPrefix(d, stagePath)) {
-            std::string suffix = d.substr(strlen(stagePath));
+            d.erase(0, strlen(stagePath));
-            d = cmStrCat(installPrefix, '/', suffix);
+            d = cmStrCat(installPrefix, '/', d);
             cmSystemTools::ConvertToUnixSlashes(d);
           }
           if (emitted.insert(d).second) {

Source/cmRST.cxx

@@ -89,7 +89,8 @@ void cmRST::ProcessModule(std::istream& is)
         this->ProcessLine(line);
       } else {
         if (line[0] != '#') {
-          this->ProcessLine(line.substr(0, pos));
+          line.resize(pos);
+          this->ProcessLine(line);
         }
         rst.clear();
         this->Reset();
@@ -103,7 +104,8 @@ void cmRST::ProcessModule(std::istream& is)
           continue;
         }
         if (cmHasLiteralPrefix(line, "# ")) {
-          this->ProcessLine(line.substr(2));
+          line.erase(0, 2);
+          this->ProcessLine(line);
           continue;
         }
         rst.clear();

Tests/RunCMake/GenerateExportHeader/exportheader_test.cpp

@@ -32,14 +32,14 @@ void compare(const char* refName, const char* testName)
     // trailing null to the string that we need to strip before testing for a
     // trailing space.
     if (refLine.size() && refLine[refLine.size() - 1] == 0) {
-      refLine = refLine.substr(0, refLine.size() - 1);
+      refLine.resize(refLine.size() - 1);
     }
     if (testLine.size() && testLine[testLine.size() - 1] == 0) {
-      testLine = testLine.substr(0, testLine.size() - 1);
+      testLine.resize(testLine.size() - 1);
     }
     // The reference files never have trailing spaces:
     if (testLine.size() && testLine[testLine.size() - 1] == ' ') {
-      testLine = testLine.substr(0, testLine.size() - 1);
+      testLine.resize(testLine.size() - 1);
     }
     if (refLine != testLine) {
       std::cout << "Ref and test are not the same:\n  Ref:  \"" << refLine