diff --git a/gui/librarydialog.cpp b/gui/librarydialog.cpp
index e48e68e1c88..085339bfc75 100644
--- a/gui/librarydialog.cpp
+++ b/gui/librarydialog.cpp
@@ -167,7 +167,7 @@ void LibraryDialog::saveCfg()
 void LibraryDialog::saveCfgAs()
 {
     const QString filter(tr("Library files (*.cfg)"));
-    const QString path = Path::getPathFromFilename(mFileName.toStdString()).c_str();
+    const QString path = QString::fromStdString(Path::getPathFromFilename(mFileName.toStdString()));
     QString selectedFile = QFileDialog::getSaveFileName(this,
                                                         tr("Save the library as"),
                                                         path,
diff --git a/lib/checkstl.cpp b/lib/checkstl.cpp
index c4827157988..19c27531976 100644
--- a/lib/checkstl.cpp
+++ b/lib/checkstl.cpp
@@ -1959,6 +1959,55 @@ static bool isLocal(const Token *tok)
     return var && !var->isStatic() && var->isLocal();
 }
 
+static bool isc_strCall(const Token* tok)
+{
+    if (!Token::simpleMatch(tok, "("))
+        return false;
+    const Token* dot = tok->astOperand1();
+    if (!Token::simpleMatch(dot, "."))
+        return false;
+    const Token* obj = dot->astOperand1();
+    if (!obj || !obj->valueType() || !obj->valueType()->container || !obj->valueType()->container->stdStringLike)
+        return false;
+    return Token::Match(dot->astOperand2(), "c_str|data ( )");
+}
+
+static bool isc_strConcat(const Token* tok)
+{
+    if (!Token::simpleMatch(tok, "+"))
+        return false;
+    const Token* cstr = nullptr;
+    for (const Token* op : { tok->astOperand1(), tok->astOperand2() }) {
+        if (isc_strCall(op)) {
+            cstr = op;
+            break;
+        }
+    }
+    if (!cstr)
+        return false;
+    const Token* strTok = (cstr == tok->astOperand1()) ? tok->astOperand2() : tok->astOperand1();
+    return strTok->valueType() && strTok->valueType()->container && strTok->valueType()->container->stdStringLike;
+}
+
+static bool isc_strAssignment(const Token* tok)
+{
+    if (!Token::simpleMatch(tok, "="))
+        return false;
+    if (!isc_strCall(tok->astOperand2()))
+        return false;
+    const Token* strTok = tok->astOperand1();
+    return strTok && strTok->valueType() && strTok->valueType()->container && strTok->valueType()->container->stdStringLike;
+}
+
+static bool isc_strConstructor(const Token* tok)
+{
+    if (!Token::Match(tok, "%var% (|{"))
+        return false;
+    if (!isc_strCall(tok->tokAt(1)->astOperand2()))
+        return false;
+    return tok->valueType() && tok->valueType()->container && tok->valueType()->container->stdStringLike;
+}
+
 namespace {
     const std::set<std::string> stl_string_stream = {
         "istringstream", "ostringstream", "stringstream", "wstringstream"
@@ -2027,16 +2076,14 @@ void CheckStl::string_c_str()
                     const Variable* var2 = tok->tokAt(2)->variable();
                     if (var->isPointer() && var2 && var2->isStlType(stl_string_stream))
                         string_c_strError(tok);
+                } else if (printPerformance && isc_strAssignment(tok->tokAt(1))) {
+                    string_c_strAssignment(tok, tok->variable()->getTypeName());
                 } else if (Token::Match(tok->tokAt(2), "%name% (") &&
                            Token::Match(tok->linkAt(3), ") . c_str|data ( ) ;") &&
                            tok->tokAt(2)->function() && Token::Match(tok->tokAt(2)->function()->retDef, "std :: string|wstring %name%")) {
                     const Variable* var = tok->variable();
                     if (var->isPointer())
                         string_c_strError(tok);
-                } else if (printPerformance && tok->tokAt(1)->astOperand2() && Token::Match(tok->tokAt(1)->astOperand2()->tokAt(-3), "%var% . c_str|data ( ) ;")) {
-                    const Token* vartok = tok->tokAt(1)->astOperand2()->tokAt(-3);
-                    if ((tok->variable()->isStlStringType() || tok->variable()->isStlStringViewType()) && vartok->variable() && vartok->variable()->isStlStringType())
-                        string_c_strAssignment(tok, tok->variable()->getTypeName());
                 }
             } else if (printPerformance && tok->function() && Token::Match(tok, "%name% ( !!)") && tok->str() != scope.className) {
                 const auto range = c_strFuncParam.equal_range(tok->function());
@@ -2068,13 +2115,9 @@ void CheckStl::string_c_str()
                         }
                     }
                 }
-            } else if (printPerformance && Token::Match(tok, "%var% (|{ %var% . c_str|data ( ) !!,") &&
-                       tok->variable() && (tok->variable()->isStlStringType() || tok->variable()->isStlStringViewType()) &&
-                       tok->tokAt(2)->variable() && tok->tokAt(2)->variable()->isStlStringType()) {
+            } else if (printPerformance && isc_strConstructor(tok)) {
                 string_c_strConstructor(tok, tok->variable()->getTypeName());
-            } else if (printPerformance && tok->next() && tok->next()->variable() && tok->next()->variable()->isStlStringType() && tok->valueType() && tok->valueType()->type == ValueType::CONTAINER &&
-                       ((Token::Match(tok->previous(), "%var% + %var% . c_str|data ( )") && tok->previous()->variable() && tok->previous()->variable()->isStlStringType()) ||
-                        (Token::Match(tok->tokAt(-5), "%var% . c_str|data ( ) + %var%") && tok->tokAt(-5)->variable() && tok->tokAt(-5)->variable()->isStlStringType()))) {
+            } else if (printPerformance && isc_strConcat(tok)) {
                 string_c_strConcat(tok);
             } else if (printPerformance && Token::simpleMatch(tok, "<<") && tok->astOperand2() && Token::Match(tok->astOperand2()->astOperand1(), ". c_str|data ( )")) {
                 const Token* str = tok->astOperand2()->astOperand1()->astOperand1();
diff --git a/test/teststl.cpp b/test/teststl.cpp
index cc4856628df..aafdf353a60 100644
--- a/test/teststl.cpp
+++ b/test/teststl.cpp
@@ -4680,6 +4680,39 @@ class TestStl : public TestFixture {
               "    return s->x.c_str();\n"
               "}\n");
         ASSERT_EQUALS("", errout_str());
+
+        check("std::string f(const std::string& s) {\n" // #14533
+              "    auto x = std::string(\"abc\") + s.c_str();\n"
+              "    auto y = s.c_str() + std::string(\"def\");\n"
+              "    return x + y;\n"
+              "}\n");
+        ASSERT_EQUALS("[test.cpp:2:33]: (performance) Concatenating the result of c_str() and a std::string is slow and redundant. [stlcstrConcat]\n"
+                      "[test.cpp:3:24]: (performance) Concatenating the result of c_str() and a std::string is slow and redundant. [stlcstrConcat]\n",
+                      errout_str());
+
+        check("std::string get();\n"
+              "std::string f(const std::string& s) {\n"
+              "    return get() + s.c_str();\n"
+              "}\n");
+        ASSERT_EQUALS("[test.cpp:3:18]: (performance) Concatenating the result of c_str() and a std::string is slow and redundant. [stlcstrConcat]\n",
+                      errout_str());
+
+        check("std::string get();\n" // #14536
+              "    std::string f(const std::string& s) {\n"
+              "    return s + get().c_str();\n"
+              "}\n");
+        ASSERT_EQUALS("[test.cpp:3:14]: (performance) Concatenating the result of c_str() and a std::string is slow and redundant. [stlcstrConcat]\n",
+                      errout_str());
+
+        check("std::string get();\n"
+              "std::string f(std::string & s) {\n"
+              "    s = get().c_str();\n"
+              "    std::string s2{ get().c_str() };\n"
+              "    return s2;\n"
+              "}\n");
+        ASSERT_EQUALS("[test.cpp:3:5]: (performance) Assigning the result of c_str() to a std::string is slow and redundant. [stlcstrAssignment]\n"
+                      "[test.cpp:4:17]: (performance) Constructing a std::string from the result of c_str() is slow and redundant. [stlcstrConstructor]\n",
+                      errout_str());
     }
 
     void uselessCalls() {