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Fix #14533, #14536 FN stlcstrConcat, stlcstrAssignment, stlcstrConstructor #8261

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Fix #14533, #14536 FN stlcstrConcat, stlcstrAssignment, stlcstrConstructor #8261

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5f7d92b
Update checkstl.cpp
chrchr-github Feb 25, 2026
0ec9223
Update teststl.cpp
chrchr-github Feb 25, 2026
d4269dd
Update checkstl.cpp
chrchr-github Feb 25, 2026
4614417
Fix #14536 FN stlcstrConcat with function returning string
web-flow Feb 25, 2026
a8bdf5f
Check operand
web-flow Feb 25, 2026
6559527
Update checkstl.cpp
chrchr-github Feb 26, 2026
1eafc89
Update teststl.cpp
chrchr-github Feb 26, 2026
82b2a0f
Update teststl.cpp
chrchr-github Feb 26, 2026
f6b00d6
Update librarydialog.cpp
chrchr-github Feb 26, 2026
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2 changes: 1 addition & 1 deletion gui/librarydialog.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -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()));
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@chrchr-github chrchr-github Feb 26, 2026

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We have stdStringLike strings in qt.cfg, sfml.cfg and wxwidgets.cfg, which all have conversion functions to/from std::string. So it should be OK to warn if the types don't match. I guess converting e.g. a QString to a wxString is pretty rare.

QString selectedFile = QFileDialog::getSaveFileName(this,
tr("Save the library as"),
path,
Expand Down
63 changes: 53 additions & 10 deletions lib/checkstl.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -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;
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@danmar danmar Feb 26, 2026

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gcc does not complain about this weird code:

#include <string>

int main() {
    std::string s;
    auto a = + s.c_str();
    return 0;
}

}

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"
Expand Down Expand Up @@ -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());
Expand Down Expand Up @@ -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();
Expand Down
33 changes: 33 additions & 0 deletions test/teststl.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -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() {
Expand Down
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