C-要求加入非结构或联合的成员

Question

Long story short I am trying to access a function inside one of my structures. Below is a simplified verson of my code:

#include <stdio.h>

typedef struct
{
    void *data;
} A_t;

typedef struct
{
    void (*function)(void);
} B_t;

void myfunction(void)
{
    fprintf(stdout, "Hello world.\n");
}

int main(int p_argc, char *p_argv[])
{
    A_t A;
    B_t B;

    B.function = myfunction;
    A.data = &B;
    A.data.function();

    return 0;
}

When trying to compile this code I get:

main.c:24:11: error: request for member ‘function’ in something not a structure or union
 A.data.function();

Could somebody explain me how to properly access this function via the A-structure?

Thanks

Answer 1

data is of type void *, you need to type cast before de-referencing.

#include <stdio.h>

typedef struct
{
    void *data;
} A_t;

typedef struct
{
    void (*function)(void);
} B_t;

void myfunction(void)
{
    fprintf(stdout, "Hello world.\n");
}

int main(int p_argc, char *p_argv[])
{
    A_t A;
    B_t B;

    B.function = myfunction;
    A.data = &B;
    ((B_t*)(A.data))->function();

    return 0;
}