sa_handler : cannot assign a value of type "void" to an entity of type "void (*)(int)-CodePudding

I'm doing a work for school, this example works on a Linux machine. I'm trying it on my Mac but it doesn't work, and as I know this should work but I can't figure out why.

#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <time.h>
#include <unistd.h>

struct sigaction act_fils, act_pere;

int pid;
void fonction_fils(){
    printf("Temperature : %d", rand() % 31   10);
    fflush(stdout);
}

void fonction_pere(){
    kill(pid,SIGUSR1); // Permet d'envoyer un signal au fils 
    alarm(5);
}

int main(){
    srand(time(NULL)); 
    pid=fork();
    if (pid==0){
        act_fils.sa_handler= fonction_fils();
        sigaction(SIGUSR1, &act_fils, NULL);
        while(1) {
            pause();
        }
    }
    else{
        act_pere.sa_handler=fonction_pere();
        sigaction(SIGALRM, &act_pere, NULL);
        alarm(5);
        while(1){
            sleep(1);
            printf("-");
            fflush(stdout);
        }
    } 
    return 0; 
}

And this is the error "cannot assign a value of type "void" to an entity of type "void (*)(int)" " on the sa_handler. Can you help me plz ? Thanks a lot !

CodePudding user response：

Firstly, when your program is preparing the binding of signal handler, it is not not calling the function at that time.

You want to obtain the function itself as a pointer object, and store that, without calling the function:

act_fils.sa_handler= fonction_fils; // no function call () parentheses

Secondly, the function has to have the right type for a signal handler:

void fonction_fils(int sig)
{
}

Note that in the C language, unlike C , if you declare a function paramter list as (), it declares the function as having an unknown parameter type information. The function definition is one that takes no arguments, compatible with (void), but as a declaration it doesn't say that to the surrounding program.

CodePudding user response：

Instead of statements like these

act_fils.sa_handler= fonction_fils();

and

act_pere.sa_handler=fonction_pere();

where there are used function calls that have the return type void you need to write

act_fils.sa_handler= fonction_fils;

and

act_pere.sa_handler=fonction_pere;

to assign function pointers.

Pay attention to that for example the data member sa_handler has the type

void     (*sa_handler)(int);

So the corresponding function shall have the same type.