CODEWITHSUNDEEP
c++g++compiler-warningsclang++
einpoklum
einpoklum

Reputation: 131445

How to trigger a warning when a certain function is called (not compiled)?

If we write:

void foo() {
#warning "Danger Will Robinson!"
}

we'll get a warning when compiling foo(). Now, What I want to do is for the compilation not to emit a warning, but for a warning to be emitted if foo() is called.

Is that possible, using g++ and/or clang++?

Note: This question is somewhat similar to this one, about marking functions as "deprecated" (a-la C++14's [[deprecated]] attribute). However, it's a different semantic. I do not want people to get the notion that my function is deprecated, but rather get a custom warning.

Upvotes: 3

Views: 1383

Answers (2)

Aykhan Hagverdili
Aykhan Hagverdili

Reputation: 29955

C++11 added _Pragma, which is like #pragma but macros can expand to it. So, you can make a macro, that expands to this warning and the function:

#include <cstdio>

void foo() {
  std::puts("foo is called!");
}

#define foo(...) _Pragma("message \"Danger Will Robinson!\"") \
  foo(__VA_ARGS__)

int main() { 
  foo(); 
}

The main issue with this approach is that it will not respect overloads and warn on any function with the name foo.

Upvotes: 4

einpoklum
einpoklum

Reputation: 131445

A suggestion from @StoryTeller in the comments, which works - partially - in GCC:

 __attribute__ ((warning ("Danger Will Robinson!"))) 
void foo() { }

int bar() {
    const int x = 123;
    foo();
    return x;
}

Why "partially"? As @StoryTeller says:

Dead code elimination can remove the warning should the call be on the eliminated branch

Have look at This GodBolt example: When you enable optimizations so that the function is inlined - the warning attribute is ignored.

Upvotes: 0

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