Refactorizations optimizing std::string usage:

1) Added global static const std::string emptyString; object:
-> Replaces some static variables in functions which might be not threadsafe
-> Avoids constructor call (std::string::string(""))
-> Even functions that return an empty string in some branches can return by reference now.
Added to config.h to ensure that it is available everywhere

2) Added overloads for TestFixture::assertEquals for the most common use cases:
-> Moves conversion from const char[] to std::string into a function, reducing code duplication in binary.

lib/checkbufferoverrun.cpp

@@ -1069,7 +1069,7 @@ void CheckBufferOverrun::checkScope(const Token *tok, const std::vector<std::str
             (declarationId == 0 && Token::Match(tok, ("strcpy|strcat ( " + varnames + " , %str% )").c_str()))) {
             const std::size_t len = Token::getStrLength(tok->tokAt(varcount + 4));
             if (total_size > 0 && len >= (unsigned int)total_size) {
-                bufferOverrunError(tok, declarationId > 0 ? std::string() : varnames);
+                bufferOverrunError(tok, declarationId > 0 ? emptyString : varnames);
                 continue;
             }
         } else if ((declarationId > 0 && Token::Match(tok, "strcpy|strcat ( %varid% , %var% )", declarationId)) ||

lib/checkbufferoverrun.h

@@ -210,8 +210,8 @@ private:
 
     static bool isArrayOfStruct(const Token* tok, int &position);
     void arrayIndexOutOfBoundsError(const std::list<const Token *> &callstack, const ArrayInfo &arrayInfo, const std::vector<MathLib::bigint> &index);
-    void bufferOverrunError(const Token *tok, const std::string &varnames = "");
-    void bufferOverrunError(const std::list<const Token *> &callstack, const std::string &varnames = "");
+    void bufferOverrunError(const Token *tok, const std::string &varnames = emptyString);
+    void bufferOverrunError(const std::list<const Token *> &callstack, const std::string &varnames = emptyString);
     void strncatUsageError(const Token *tok);
     void negativeMemoryAllocationSizeError(const Token *tok); // provide a negative value to memory allocation function
     void outOfBoundsError(const Token *tok, const std::string &what, const bool show_size_info, const MathLib::bigint &supplied_size, const MathLib::bigint &actual_size);

lib/config.h

@@ -19,4 +19,7 @@
 #  include <crtdbg.h>
 #endif
 
+#include <string>
+static const std::string emptyString;
+
 #endif // configH

lib/errorlogger.h

@@ -217,8 +217,8 @@ public:
          * @param outputFormat Empty string to use default output format
          * or template to be used. E.g. "{file}:{line},{severity},{id},{message}"
         * @return formatted string
-               */
-        std::string toString(bool verbose, const std::string &outputFormat = "") const;
+         */
+        std::string toString(bool verbose, const std::string &outputFormat = emptyString) const;
 
         std::string serialize() const;
         bool deserialize(const std::string &data);

lib/library.h

@@ -184,9 +184,9 @@ public:
 
     bool isargvalid(const std::string &functionName, int argnr, const MathLib::bigint argvalue) const;
 
-    std::string validarg(const std::string &functionName, int argnr) const {
+    const std::string& validarg(const std::string &functionName, int argnr) const {
         const ArgumentChecks *arg = getarg(functionName, argnr);
-        return arg ? arg->valid : std::string("");
+        return arg ? arg->valid : emptyString;
     }
 
     bool markupFile(const std::string &path) const {
@@ -227,24 +227,24 @@ public:
         return offset;
     }
 
-    std::string blockstart(const std::string &file) const {
+    const std::string& blockstart(const std::string &file) const {
         const std::map<std::string, CodeBlock>::const_iterator map_it
             = _executableblocks.find(Path::getFilenameExtensionInLowerCase(file));
 
         if (map_it != _executableblocks.end()) {
             return map_it->second.start();
         }
-        return std::string();
+        return emptyString;
     }
 
-    std::string blockend(const std::string &file) const {
+    const std::string& blockend(const std::string &file) const {
         const std::map<std::string, CodeBlock>::const_iterator map_it
             = _executableblocks.find(Path::getFilenameExtensionInLowerCase(file));
 
         if (map_it != _executableblocks.end()) {
             return map_it->second.end();
         }
-        return std::string();
+        return emptyString;
     }
 
     bool iskeyword(const std::string &file, const std::string &keyword) const {

lib/preprocessor.cpp

@@ -1040,7 +1040,7 @@ void Preprocessor::preprocess(std::istream &srcCodeStream, std::string &processe
         processedFile = ostr.str();
     }
 
-    std::map<std::string, std::string> defs(getcfgmap(_settings ? _settings->userDefines : std::string(""), _settings, filename));
+    std::map<std::string, std::string> defs(getcfgmap(_settings ? _settings->userDefines : emptyString, _settings, filename));
 
     if (_settings && _settings->_maxConfigs == 1U) {
         std::set<std::string> pragmaOnce;

lib/suppressions.h

@@ -99,7 +99,7 @@ public:
      * @param line number, e.g. "123"
      * @return error message. empty upon success
      */
-    std::string addSuppression(const std::string &errorId, const std::string &file = "", unsigned int line = 0);
+    std::string addSuppression(const std::string &errorId, const std::string &file = emptyString, unsigned int line = 0);
 
     /**
      * @brief Returns true if this message should not be shown to the user.

lib/symboldatabase.h

@@ -104,8 +104,7 @@ public:
     }
 
     const std::string& name() const {
-        static const std::string empty;
-        return classDef->next()->isName() ? classDef->strAt(1) : empty;
+        return classDef->next()->isName() ? classDef->strAt(1) : emptyString;
     }
 
     const Token *initBaseInfo(const Token *tok, const Token *tok1);
@@ -215,13 +214,11 @@ public:
      * @return name string
      */
     const std::string &name() const {
-        static const std::string noname;
-
         // name may not exist for function arguments
         if (_name)
             return _name->str();
 
-        return noname;
+        return emptyString;
     }
 
     /**

lib/token.cpp

@@ -266,10 +266,8 @@ const Token *Token::linkAt(int index) const
 
 const std::string &Token::strAt(int index) const
 {
-    static const std::string empty_str;
-
     const Token *tok = this->tokAt(index);
-    return tok ? tok->_str : empty_str;
+    return tok ? tok->_str : emptyString;
 }
 
 static int multiComparePercent(const Token *tok, const char ** haystack_p,

lib/tokenize.h

@@ -90,7 +90,7 @@ public:
      */
     bool tokenize(std::istream &code,
                   const char FileName[],
-                  const std::string &configuration = "",
+                  const std::string &configuration = emptyString,
                   bool noSymbolDB_AST = false);
     /**
      * tokenize condition and run simple simplifications on it

lib/tokenlist.cpp

@@ -56,8 +56,7 @@ TokenList::~TokenList()
 const std::string& TokenList::getSourceFilePath() const
 {
     if (getFiles().empty()) {
-        static const std::string empty;
-        return empty;
+        return emptyString;
     }
     return getFiles()[0];
 }

lib/tokenlist.h

@@ -73,7 +73,7 @@ public:
      * @param code input stream for code
      * @param file0 source file name
      */
-    bool createTokens(std::istream &code, const std::string& file0 = "");
+    bool createTokens(std::istream &code, const std::string& file0 = emptyString);
 
     /** Deallocate list */
     void deallocateTokens();

test/testsuite.cpp

@@ -149,6 +149,18 @@ void TestFixture::assertEquals(const char *filename, unsigned int linenr, const
         }
     }
 }
+void TestFixture::assertEquals(const char *filename, unsigned int linenr, const char expected[], const std::string& actual, const std::string &msg) const
+{
+    assertEquals(filename, linenr, std::string(expected), actual, msg);
+}
+void TestFixture::assertEquals(const char *filename, unsigned int linenr, const char expected[], const char actual[], const std::string &msg) const
+{
+    assertEquals(filename, linenr, std::string(expected), std::string(actual), msg);
+}
+void TestFixture::assertEquals(const char *filename, unsigned int linenr, const std::string& expected, const char actual[], const std::string &msg) const
+{
+    assertEquals(filename, linenr, expected, std::string(actual), msg);
+}
 
 void TestFixture::assertEquals(const char *filename, unsigned int linenr, long long expected, long long actual, const std::string &msg) const
 {

test/testsuite.h

@@ -52,9 +52,12 @@ protected:
     void assert_(const char *filename, unsigned int linenr, bool condition) const;
     void todoAssert(const char *filename, unsigned int linenr, bool condition) const;
 
-    void assertEquals(const char *filename, unsigned int linenr, const std::string &expected, const std::string &actual, const std::string &msg = "") const;
-    void assertEquals(const char *filename, unsigned int linenr, long long expected, long long actual, const std::string &msg="") const;
-    void assertEqualsDouble(const char *filename, unsigned int linenr, double expected, double actual, const std::string &msg="") const;
+    void assertEquals(const char *filename, unsigned int linenr, const std::string &expected, const std::string &actual, const std::string &msg = emptyString) const;
+    void assertEquals(const char *filename, unsigned int linenr, const char expected[], const std::string& actual, const std::string &msg = emptyString) const;
+    void assertEquals(const char *filename, unsigned int linenr, const char expected[], const char actual[], const std::string &msg = emptyString) const;
+    void assertEquals(const char *filename, unsigned int linenr, const std::string& expected, const char actual[], const std::string &msg = emptyString) const;
+    void assertEquals(const char *filename, unsigned int linenr, long long expected, long long actual, const std::string &msg = emptyString) const;
+    void assertEqualsDouble(const char *filename, unsigned int linenr, double expected, double actual, const std::string &msg = emptyString) const;
 
     void todoAssertEquals(const char *filename, unsigned int linenr, const std::string &wanted,
                           const std::string &current, const std::string &actual) const;

test/testsuppressions.cpp

@@ -115,7 +115,7 @@ private:
     }
 
     // Check the suppression
-    void checkSuppression(const char code[], const std::string &suppression = "") {
+    void checkSuppression(const char code[], const std::string &suppression = emptyString) {
         // Clear the error log
         errout.str("");
 
@@ -133,7 +133,7 @@ private:
         reportUnmatchedSuppressions(settings.nomsg.getUnmatchedGlobalSuppressions());
     }
 
-    void checkSuppressionThreads(const char code[], const std::string &suppression = "") {
+    void checkSuppressionThreads(const char code[], const std::string &suppression = emptyString) {
         errout.str("");
         output.str("");
 
@@ -157,7 +157,7 @@ private:
     }
 
     // Check the suppression for multiple files
-    void checkSuppression(const char *names[], const char *codes[], const std::string &suppression = "") {
+    void checkSuppression(const char *names[], const char *codes[], const std::string &suppression = emptyString) {
         // Clear the error log
         errout.str("");