Suppress gcc warning when using function pointers with void* argument

Question

Let's say I have function accepting function pointer as argument.

void fun(void(*problematicFunPointer)(void*) problemFun){
...
}

Then, when I want to use this function like this:

void actualProblematicFun1(struct s_something * smt){
...
}

void actualProblematicFun2(struct s_something_else * smthels){
...
}

int main(){
    fun(&actualProblematicFun1);
    fun(&actualProblematicFun2);
}

When using -Werror, this throws compile error -Werror=incompatible-pointer-types. Is there a way to suppress warning for this particular case?

AFAIK, not without effectively casting the pointer to void(*)(void*). Calling the resultant pointer is then technically undefined behavior, although practically it works and is (AFAIK) the only way to get that better codegen. The C standard would want you to write a wrapper function and pass a pointer to that. — Petr Skocik
– Petr Skocik, Commented Jan 15, 2022 at 0:26
casting to void()(void) would help in this case. but in my project, I use more function types with more that 1 argument. for example void()(void, int , char), so I would have to cast all of them to their respective "voided" types. I took care to not mess up with possible undefined behavior when using function like this, so as you said, it should practicaly work. It is just problem that when I compile with -Werror, the output is flooded with this one warning and makes it hard to read. — plomba
– plomba, Commented Jan 15, 2022 at 0:38

KamilCuk · Accepted Answer · 2022-01-15 01:27:28Z

1

Is there a way to suppress warning for this particular case?

Write the actual functions with proper argument type that matches the declaration.

void actualProblematicFun1(struct s_something * smt){
...
}

void actualProblematicFun2(struct s_something_else * smthels){
...
}

void actualProblematicFun1Trampoline(void *smt) {
   actualProblematicFun1(smt);
}

void actualProblematicFun2Trampoline(void *smthels) {
    actualProblematicFun2(smthels);
}


int main(){
    fun(&actualProblematicFun1Trampoline);
    fun(&actualProblematicFun2Trampoline);
}

answered Jan 15, 2022 at 1:27

KamilCuk

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