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Fix #1473: warn when fclose() is used as a while loop condition #8444

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Fix #1473: warn when fclose() is used as a while loop condition #8444

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22917dd
Fix #1473: warn when fclose() is used as a while loop condition
francois-berder Apr 12, 2026
8800ee5
fixup! Fix #1473: warn when fclose() is used as a while loop condition
francois-berder Apr 27, 2026
2f52148
fixup! fixup! Fix #1473: warn when fclose() is used as a while loop c…
francois-berder Apr 27, 2026
c2c3e53
fixup! fixup! fixup! Fix #1473: warn when fclose() is used as a while…
francois-berder Apr 28, 2026
28f2247
fixup! fixup! fixup! fixup! Fix #1473: warn when fclose() is used as …
francois-berder Apr 29, 2026
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29 changes: 29 additions & 0 deletions lib/checkio.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -245,6 +245,35 @@ void CheckIO::checkFileUsage()
} else if (tok->str() == "fclose") {
fileTok = tok->tokAt(2);
operation = Filepointer::Operation::CLOSE;

// #1473 Check if fclose is in a while loop condition
if (fileTok && fileTok->isVariable()) {
const Token* tmp = tok->astParent();
const Token* loopTok = nullptr;
while (tmp) {
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@danmar danmar Apr 30, 2026

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could we use Token::astTop() here instead of the loop?

if (Token::simpleMatch(tmp->previous(), "while (")) {
loopTok = tmp->previous();
break;
}
tmp = tmp->astParent();
}
if (loopTok) {
const Token* bodyEnd = nullptr;
const Token* bodyStart = nullptr;

if (Token::simpleMatch(loopTok->previous(), "}") && Token::simpleMatch(loopTok->linkAt(-1)->previous(), "do")) { // Handle do-while loops
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@danmar danmar Apr 30, 2026 •
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I would spontanously prefer that we look at the scope type.

    if (Token::simpleMatch(loopTok->previous(), "}") &&
        loopTok->previous()->scope()->scopeType == Scope::ScopeType::eDo)

bodyEnd = loopTok->previous();
bodyStart = bodyEnd->link();
} else {
bodyStart = loopTok->linkAt(1)->next();
bodyEnd = bodyStart->link();
}

// Do not trigger a warning if the loop always exits or if the file is opened again in the loop.
if (!isReturnScope(bodyEnd, mSettings->library) && Token::findmatch(bodyStart, "%var% =", bodyEnd, fileTok->varId()) == nullptr)
useClosedFileError(tok);
}
}
} else if (whitelist.find(tok->str()) != whitelist.end()) {
fileTok = tok->tokAt(2);
if ((tok->str() == "ungetc" || tok->str() == "ungetwc") && fileTok)
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24 changes: 23 additions & 1 deletion test/testio.cpp
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Expand Up @@ -544,7 +544,29 @@ class TestIO : public TestFixture {
" FILE *a = fopen(\"aa\", \"r\");\n"
" while (fclose(a)) {}\n"
"}");
TODO_ASSERT_EQUALS("[test.cpp:3:5]: (error) Used file that is not opened. [useClosedFile]\n", "", errout_str());
ASSERT_EQUALS("[test.cpp:3:12]: (error) Used file that is not opened. [useClosedFile]\n", errout_str());
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check("void foo() {\n"
" FILE *a = fopen(\"aa\", \"r\");\n"
" while (fclose(a)) {\n"
" break;\n"
" }\n"
"}");
ASSERT_EQUALS("", errout_str());

check("void foo() {\n"
" FILE *a = fopen(\"aa\", \"r\");\n"
" while (fclose(a)) {\n"
" a = fopen(\"aa\", \"r\");\n"
" }\n"
"}");
ASSERT_EQUALS("", errout_str());

check("void foo() {\n"
" FILE *a = fopen(\"aa\", \"r\");\n"
" do {} while (fclose(a));\n"
"}");
ASSERT_EQUALS("[test.cpp:3:18]: (error) Used file that is not opened. [useClosedFile]\n", errout_str());
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@danmar danmar Apr 30, 2026

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I am not sure about the message. The file is opened but not in the loop. The first loop iteration it works fine. I don't know how I would like to phraze it... here is a rough idea:

File handle 'a' can be closed more than once in loop. 'a' is not opened in the loop.

Feel free to suggest something better.


// #6823
check("void foo() {\n"
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