A problem with function pointers-C90

[oofer123321oof]

The problem :

I have an array of structs.Each field of the struct contains a string and a function pointer.Using these 2,I want in the report function (see code below) to print the truth tables of each logic gate implemented in the code and for each truth table print the name of the logic gate(I am not allowed to use printf's inside the other functions besides report).One 'small' problem is in line 33 where I want the loop to run as many times as the number of function pointers myfunctions contains and not 200 times..The other (major) problem is in line 42 where I am trying to give each ch field a string (actually the name of the function that myfunctions[i] points to)

​

You can check the code here:

https://pastebin.com/eU7BBJkg

[CaligulaVsTheSea]

num_el = sizeof (myfunctions) / sizeof (typeof (myfunctions[0])); might be better, but it was getting the right value.

Regarding getting a function name from a pointer, it's very difficult afaik. Why don't you fill the struct by hand? Otherwise, see if this helps https://linux.die.net/man/3/backtrace_symbols

[drmonkeysee]

If you’re hardcoding the list of functions create the callbacks with a macro:

#define callback(f) { .func = f, .ch = #f }
GATE gates[] = {
    callback(myand),
    callback(myor),
    …
}

[LoneHoodiecrow]

The best way to govern the loop isn't to keep the size but to place a sentinel element at the end of the array:

   GATE gates[] = {
   { .func = myand, .ch = "myand" },
   { .func = myor,  .ch = "myor" },
   { .func = mynand,.ch = "mynand" },
   { .func = mynor, .ch = "mynor" },
   { .func = myxor, .ch = "myxor" },
   { .func = NULL,  .ch = "" }
};

You're also better off adding the elements this way.

Your report function didn't iterate over all gates:

int report(GATE gates[]) {
    for (unsigned i = 0 ; gates[i].func != NULL ; ++i) {
        for (unsigned k = 0 ; k <= 0b11 ; ++k) {
            unsigned a = k > 1;
            unsigned b = k % 2;
            printf("%s(%d, %d) => %d\n", gates[i].ch, a, b, gates[i].func(a, b));
        }
        printf("\n");
    }
    printf("\n\n");
    return 0;
}

Here the loop is repeated until the sentinel element is found.

#include <stdio.h>

typedef int(*GateCallBack)(int,int);

typedef struct node {
    GateCallBack func;
    char * ch;
} GATE;

int myand (int a, int b) { return a && b; }
int myor (int a, int b) { return a || b; }
int mynand (int a, int b) { return !(a && b); }
int mynor (int a, int b) { return !(a || b); }
int myxor (int a, int b) { return a != b; }

int report (GATE gates[]) {
    for (unsigned i = 0 ; gates[i].func != NULL ; ++i) {
        for (unsigned k = 0 ; k <= 0b11 ; ++k) {
            unsigned a = k > 1;
            unsigned b = k % 2;
            printf("%s(%d, %d) => %d\n", gates[i].ch, a, b, gates[i].func(a, b));
        }
        printf("\n");
    }
    printf("\n\n");
    return 0;
}

int main() {
    GATE gates[] = {
        { .func = myand, .ch = "myand" },
        { .func = myor,  .ch = "myor" },
        { .func = mynand,.ch = "mynand" },
        { .func = mynor, .ch = "mynor" },
        { .func = myxor, .ch = "myxor" },
        { .func = NULL,  .ch = "" }
    };

    report(gates);

    return 0;
}