https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82924
Bug ID: 82924
Summary: gcc gives no warning for comparing unsigned integer <
0 even with -Wextra enabled
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: jure.slak at ijs dot si
Target Milestone: ---
Created attachment 42568
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=42568&action=edit
Compiling this file with -Wtype-limits should give a warning, but does not.
Take the following code
#include <iostream>
template<typename T>
T f(T x, unsigned y) {
if (y < 0) return x;
return static_cast<T>(0);
}
using namespace std;
int main() {
int a = f(2, 3);
std::cout << a << std::endl;
return 0;
}
where function f clearly always returns 0. Compiling it with g++-7.2.0 -Wall
-Wextra gives no hint about pointless comparison. However, clang warns us
nicely:
a.cpp:7:11: warning: comparison of unsigned expression < 0 is always false
[-Wtautological-compare]
if (y < 0) return x;
~ ^ ~
1 warning generated.
I believe that using -Wtype-limits (part of -Wextra) should warn about this
case, as it does in the non-template version.
