Skip to content

Fix #15056 (knownconditiontruefalse: remove warnings for return result) #8877

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
danmar wants to merge 5 commits into
base: main
Choose a base branch
from
+53 −45
Open

Fix #15056 (knownconditiontruefalse: remove warnings for return result) #8877

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
5 commits
Select commit Hold shift + click to select a range
2f4c31f
Do not warn for return value that is always true/false
dmcppcheck Sep 20, 2026
fd78a1e
qt.cpp
dmcppcheck Sep 20, 2026
ad4fb8a
tweaks
dmcppcheck Sep 20, 2026
33d8cb6
2
dmcppcheck Sep 20, 2026
a9565ec
comment
dmcppcheck Sep 20, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
6 changes: 2 additions & 4 deletions lib/checkcondition.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -1532,7 +1532,7 @@ void CheckConditionImpl::alwaysTrueFalse()
tok = tok->link();
continue;
}
if (!tok->hasKnownIntValue())
if (!tok->hasKnownIntValue() || !isConstExpression(tok, mSettings.library))
continue;
const Token* condition = nullptr;
{
Expand All @@ -1549,12 +1549,10 @@ void CheckConditionImpl::alwaysTrueFalse()
condition = parent;
else if (Token::Match(parent->previous(), "if|while ("))
condition = parent->previous();
else if (Token::simpleMatch(parent, "return"))
condition = parent;
else if (parent->str() == ";" && parent->astParent() && parent->astParent()->astParent() &&
Token::simpleMatch(parent->astParent()->astParent()->previous(), "for ("))
condition = parent->astParent()->astParent()->previous();
else if (Token::Match(tok, "%comp%"))
else if ((Token::Match(tok, "%comp%|!") || isConstFunctionCall(tok->previous(), mSettings.library)) && Token::Match(tok->astParent(), "%oror%|&&"))
condition = tok;
else if (hasComp && Token::Match(tok, "!|%var%") && astIsBool(parent) && Token::Match(parent, "%assign%"))
condition = tok;
Expand Down
1 change: 0 additions & 1 deletion test/cfg/qt.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -206,7 +206,6 @@ void QString1(QString s)
bool QString2()
{
QString s;
// cppcheck-suppress knownConditionTrueFalse
return s.size();
}

Expand Down
91 changes: 51 additions & 40 deletions test/testcondition.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -1336,7 +1336,7 @@ class TestCondition : public TestFixture {
check("int f(char c) {\n"
" return (c <= 'a' && c >= 'z');\n"
"}\n"); // TODO: use s?
ASSERT_EQUALS("[test.cpp:2:13] -> [test.cpp:2:25]: (style) Return value 'c>='z'' is always false [knownConditionTrueFalse]\n", errout_str());
ASSERT_EQUALS("[test.cpp:2:13] -> [test.cpp:2:25]: (style) Condition 'c>='z'' is always false [knownConditionTrueFalse]\n", errout_str());

@danmar danmar Sep 20, 2026

Copy link
Copy Markdown
Collaborator Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

instead of knownConditionTrueFalse.. this test case reminds me more about the "mutually exclusive comparisons" checker

}

void incorrectLogicOperator7() { // opposite expressions
Expand Down Expand Up @@ -2181,7 +2181,7 @@ class TestCondition : public TestFixture {
" b = g();\n"
" return b;\n"
"}\n");
ASSERT_EQUALS("[test.cpp:2:9] -> [test.cpp:3:16]: (style) Return value '!b' is always false [knownConditionTrueFalse]\n", errout_str());
ASSERT_EQUALS("", errout_str());
}

void oppositeInnerConditionPointers() {
Expand Down Expand Up @@ -3362,16 +3362,21 @@ class TestCondition : public TestFixture {
" if(x == 0) { x++; return x == 0; }\n"
" return false;\n"
"}\n");
ASSERT_EQUALS("[test.cpp:2:8] -> [test.cpp:2:30]: (style) Return value 'x==0' is always false [knownConditionTrueFalse]\n", errout_str());
ASSERT_EQUALS("", errout_str());

check("void f() {\n" // #6898 (Token::expressionString)
" int x = 0;\n"
" A(x++ == 1);\n"
" A(x++ == 2);\n"
"}\n");
ASSERT_EQUALS("[test.cpp:3:9]: (style) Condition 'x++==1' is always false [knownConditionTrueFalse]\n"
"[test.cpp:4:9]: (style) Condition 'x++==2' is always false [knownConditionTrueFalse]\n",
errout_str());
ASSERT_EQUALS("", errout_str());

check("void f() {\n"
" int x = 0;\n"
" if (x++ == 1) {}\n" // <- no warning as there is a side effect
" if (x++ == 2) {}\n" // <- no warning as there is a side effect
"}\n");
ASSERT_EQUALS("", errout_str());

check("bool foo(int bar) {\n"
" bool ret = false;\n"
Expand Down Expand Up @@ -3585,7 +3590,7 @@ class TestCondition : public TestFixture {
" const int b = 52;\n"
" return a+b;\n"
"}\n");
ASSERT_EQUALS("[test.cpp:4:13]: (style) Return value 'a+b' is always true [knownConditionTrueFalse]\n", errout_str());
ASSERT_EQUALS("", errout_str());

check("int f() {\n"
" int a = 50;\n"
Expand Down Expand Up @@ -4175,7 +4180,7 @@ class TestCondition : public TestFixture {
check("bool f(bool a, bool b) {\n"
" return a || ! b || ! a;\n"
"}\n");
ASSERT_EQUALS("[test.cpp:2:12] -> [test.cpp:2:24]: (style) Return value '!a' is always true [knownConditionTrueFalse]\n", errout_str());
ASSERT_EQUALS("[test.cpp:2:12] -> [test.cpp:2:24]: (style) Condition '!a' is always true [knownConditionTrueFalse]\n", errout_str());

// #10148
check("void f(int i) {\n"
Expand Down Expand Up @@ -4402,8 +4407,7 @@ class TestCondition : public TestFixture {
" if (w) {}\n"
" }\n"
"}\n");
ASSERT_EQUALS("[test.cpp:4:24]: (style) Condition 'v<2' is always true [knownConditionTrueFalse]\n"
"[test.cpp:5:7]: (style) Condition 'w' is always true [knownConditionTrueFalse]\n",
ASSERT_EQUALS("[test.cpp:5:7]: (style) Condition 'w' is always true [knownConditionTrueFalse]\n",
errout_str());

check("void f(double d) {\n" // #10792
Expand Down Expand Up @@ -4506,9 +4510,12 @@ class TestCondition : public TestFixture {
"void foo() {\n"
" if (bar(1) == 0 && bar(1) > 0) {}\n"
"}\n");
ASSERT_EQUALS("[test.cpp:3:16]: (style) Condition 'bar(1)==0' is always false [knownConditionTrueFalse]\n"
"[test.cpp:3:31]: (style) Condition 'bar(1)>0' is always true [knownConditionTrueFalse]\n",
errout_str());
// TODO handle function calls without side effects better
// these warnings are shown if isConstExpression is removed from the checker
TODO_ASSERT_EQUALS("[test.cpp:3:16]: (style) Condition 'bar(1)==0' is always false [knownConditionTrueFalse]\n"
"[test.cpp:3:31]: (style) Condition 'bar(1)>0' is always true [knownConditionTrueFalse]\n",
"",
errout_str());

check("struct S { int bar(int i) const; };\n"
"void foo(const S& s) {\n"
Expand Down Expand Up @@ -4583,9 +4590,12 @@ class TestCondition : public TestFixture {
"void f() {\n"
" if (g() == 1 && g() == -1) {}\n"
"}\n");
ASSERT_EQUALS("[test.cpp:3:13]: (style) Condition 'g()==1' is always false [knownConditionTrueFalse]\n"
"[test.cpp:3:25]: (style) Condition 'g()==-1' is always true [knownConditionTrueFalse]\n",
errout_str());
// TODO handle function calls without side effects better
// these warnings are shown if isConstExpression is removed from the checker
TODO_ASSERT_EQUALS("[test.cpp:3:13]: (style) Condition 'g()==1' is always false [knownConditionTrueFalse]\n"
"[test.cpp:3:25]: (style) Condition 'g()==-1' is always true [knownConditionTrueFalse]\n",
"",
errout_str());

// #9817
check("void f(float x) {\n"
Expand All @@ -4606,8 +4616,7 @@ class TestCondition : public TestFixture {
ASSERT_EQUALS("[test.cpp:3:12]: (style) Condition '!s.empty()' is always false [knownConditionTrueFalse]\n"
"[test.cpp:4:19]: (style) Condition 's.empty()' is always true [knownConditionTrueFalse]\n"
"[test.cpp:5:16]: (style) Condition 's.empty()' is always true [knownConditionTrueFalse]\n"
"[test.cpp:6:9]: (style) Condition '(bool)0' is always false [knownConditionTrueFalse]\n"
"[test.cpp:7:19]: (style) Return value 's.empty()' is always true [knownConditionTrueFalse]\n",
"[test.cpp:6:9]: (style) Condition '(bool)0' is always false [knownConditionTrueFalse]\n",
errout_str());

check("int f(bool b) {\n"
Expand All @@ -4618,17 +4627,17 @@ class TestCondition : public TestFixture {
" if (b) return static_cast<int>(1);\n"
" return (int)0;\n"
"}\n");
ASSERT_EQUALS("[test.cpp:6:35]: (style) Return value 'static_cast<int>(1)' is always true [knownConditionTrueFalse]\n"
"[test.cpp:7:12]: (style) Return value '(int)0' is always false [knownConditionTrueFalse]\n",
errout_str());
ASSERT_EQUALS("", errout_str());

check("int f() { return 3; }\n"
"int g() { return f(); }\n"
"int h() { if (f()) {} }\n"
"int i() { return f() == 3; }\n");
ASSERT_EQUALS("[test.cpp:3:16]: (style) Condition 'f()' is always true [knownConditionTrueFalse]\n"
"[test.cpp:4:22]: (style) Return value 'f()==3' is always true [knownConditionTrueFalse]\n",
errout_str());
// TODO handle function calls without side effects better
// if the isConstExpression is removed from the checker then this warning is shown
TODO_ASSERT_EQUALS("[test.cpp:3:16]: (style) Condition 'f()' is always true [knownConditionTrueFalse]\n",
"",
errout_str());

check("int f() {\n"
" const char *n;\n"
Expand Down Expand Up @@ -4695,12 +4704,10 @@ class TestCondition : public TestFixture {
"void f() {\n"
" int i = 5;\n"
" int* p = &i;\n"
" g(i == 7);\n"
" g(p == nullptr);\n"
" g(i == 7);\n" // <- argument is always false but cannot be removed therefore warning should NOT be written
" g(p == nullptr);\n" // <- argument is always false but cannot be removed therefore warning should NOT be written
"}\n");
ASSERT_EQUALS("[test.cpp:5:9]: (style) Condition 'i==7' is always false [knownConditionTrueFalse]\n"
"[test.cpp:6:9]: (style) Condition 'p==nullptr' is always false [knownConditionTrueFalse]\n",
errout_str());
ASSERT_EQUALS("", errout_str());

check("enum E { E0, E1 };\n"
"void f() {\n"
Expand Down Expand Up @@ -4745,7 +4752,8 @@ class TestCondition : public TestFixture {
" int i = 0;\n"
" if ((i = g(), 1) != 0) {}\n"
"}\n");
ASSERT_EQUALS("[test.cpp:3:22]: (style) Condition '(i=g(),1)!=0' is always true [knownConditionTrueFalse]\n", errout_str());
// the condition is always true but we can't remove the condition therefore no warning is expected
ASSERT_EQUALS("", errout_str());

check("void f(unsigned i) {\n"
" const int a[2] = {};\n"
Expand Down Expand Up @@ -4919,9 +4927,12 @@ class TestCondition : public TestFixture {
" if (b()) {}\n"
" if (!b()) {}\n"
"}\n");
ASSERT_EQUALS("[test.cpp:3:10]: (style) Condition 'b()' is always false [knownConditionTrueFalse]\n"
"[test.cpp:4:9]: (style) Condition '!b()' is always true [knownConditionTrueFalse]\n",
errout_str());
// TODO handle function calls without side effects better
// these warnings are shown if isConstExpression is removed from the checker
TODO_ASSERT_EQUALS("[test.cpp:3:10]: (style) Condition 'b()' is always false [knownConditionTrueFalse]\n"
"[test.cpp:4:9]: (style) Condition '!b()' is always true [knownConditionTrueFalse]\n",
"",
errout_str());

check("int g();\n" // a value modified inside a nested branch must be lowered to possible
"void f(int outer, int inner) {\n"
Expand Down Expand Up @@ -5023,7 +5034,7 @@ class TestCondition : public TestFixture {
" return (index++) >= s;\n"
" }\n"
"}\n");
ASSERT_EQUALS("[test.cpp:2:15] -> [test.cpp:6:26]: (style) Return value '(index++)>=s' is always false [knownConditionTrueFalse]\n", errout_str());
ASSERT_EQUALS("", errout_str());

check("struct a {\n"
" a *b() const;\n"
Expand Down Expand Up @@ -5460,7 +5471,7 @@ class TestCondition : public TestFixture {
check("bool f(const int *p, const int *q) {\n"
" return p != NULL && q != NULL && p == NULL;\n"
"}\n");
ASSERT_EQUALS("[test.cpp:2:40]: (style) Return value 'p==NULL' is always false [knownConditionTrueFalse]\n", errout_str());
ASSERT_EQUALS("[test.cpp:2:40]: (style) Condition 'p==NULL' is always false [knownConditionTrueFalse]\n", errout_str());

check("struct S {\n" // #11789
" std::vector<int> v;\n"
Expand Down Expand Up @@ -5588,7 +5599,7 @@ class TestCondition : public TestFixture {
check("bool f(const std::string& a, const std::string& b) {\n"
" return a.empty() || (b.empty() && a.empty());\n"
"}\n");
ASSERT_EQUALS("[test.cpp:2:19] -> [test.cpp:2:46]: (style) Return value 'a.empty()' is always false [knownConditionTrueFalse]\n", errout_str());
ASSERT_EQUALS("[test.cpp:2:19] -> [test.cpp:2:46]: (style) Condition 'a.empty()' is always false [knownConditionTrueFalse]\n", errout_str());

check("struct A {\n"
" struct iterator;\n"
Expand Down Expand Up @@ -6296,7 +6307,7 @@ class TestCondition : public TestFixture {
check("bool f(const std::string &s) {\n"
" return s.size()>2U && s[0]=='4' && s[0]=='2';\n"
"}\n");
ASSERT_EQUALS("[test.cpp:2:35] -> [test.cpp:2:48]: (style) Return value 's[0]=='2'' is always false [knownConditionTrueFalse]\n", errout_str());
ASSERT_EQUALS("[test.cpp:2:35] -> [test.cpp:2:48]: (style) Condition 's[0]=='2'' is always false [knownConditionTrueFalse]\n", errout_str());

check("void f(int i) { if (i == 1 || 2) {} }\n"); // #12487
ASSERT_EQUALS("[test.cpp:1:28]: (style) Condition 'i==1||2' is always true [knownConditionTrueFalse]\n", errout_str());
Expand Down Expand Up @@ -6474,12 +6485,12 @@ class TestCondition : public TestFixture {
"}\n");
ASSERT_EQUALS("", errout_str());

// the assignments are always false/true.. but "assignment in condition" would be a different checker
// knownConditionTrueFalse should only warn if code can be removed.
check("void f(uint32_t u) {\n" // #2490
" if ((u = 0x00000000) || (u = 0xffffffff)) {}\n"
"}\n");
ASSERT_EQUALS("[test.cpp:2:12]: (style) Condition 'u=0x00000000' is always false [knownConditionTrueFalse]\n"
"[test.cpp:2:32]: (style) Condition 'u=0xffffffff' is always true [knownConditionTrueFalse]\n",
errout_str());
ASSERT_EQUALS("", errout_str());
}

void compareOutOfTypeRange() {
Expand Down
Loading