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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
c359ded
Update teststl.cpp
chrchr-github Feb 27, 2026
ed47749
isBinaryOp()
web-flow Feb 28, 2026
a271422
Restrict to STL types
web-flow Mar 2, 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()));
QString selectedFile = QFileDialog::getSaveFileName(this,
tr("Save the library as"),
path,
Expand Down
67 changes: 57 additions & 10 deletions lib/checkstl.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1959,6 +1959,59 @@ 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 ||
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@danmar danmar Mar 3, 2026

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I assume that now we will not warn for:

     QString s1 = ...;
     QString s2 = s1.c_str();

my suggestion is that we warn when the same container is used. s1 and s2 have the same container pointer. Does that sound good?

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@chrchr-github chrchr-github Mar 3, 2026

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I assume that now we will not warn for:

     QString s1 = ...;
     QString s2 = s1.c_str();

No, we won't warn, although that is a fixable issue.

my suggestion is that we warn when the same container is used. s1 and s2 have the same container pointer. Does that sound good?

We can do that, so we will also warn for

     wxString s1 = ...;
     wxString s2 = s1.c_str();

!obj->valueType()->container->stdStringLike || !obj->valueType()->container->startPatternHasStd)
return false;
return Token::Match(dot->astOperand2(), "c_str|data ( )");
}

static bool isc_strConcat(const Token* tok)
{
if (!Token::simpleMatch(tok, "+") || !tok->isBinaryOp())
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 && strTok->valueType()->container->startPatternHasStd;
}

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 && strTok->valueType()->container->startPatternHasStd;
}

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 && tok->valueType()->container->startPatternHasStd;
}

namespace {
const std::set<std::string> stl_string_stream = {
"istringstream", "ostringstream", "stringstream", "wstringstream"
Expand Down Expand Up @@ -2027,16 +2080,14 @@ 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 +2119,9 @@ 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
39 changes: 39 additions & 0 deletions test/teststl.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4680,6 +4680,45 @@ 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());

check("void f() {\n"
" std::string s;\n"
" auto a = + s.c_str();\n"
"}\n");
ASSERT_EQUALS("", errout_str());
}

void uselessCalls() {
Expand Down
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