Question

Ive been working at this problem for about a week, I have looked up plenty of “incompatible pointer type” warning solutions but I’m still confused as to how I can fix this compile error.

I get an error saying:

char_stack_interface.c: In function ‘pop_char’:
char_stack_interface.c:32: warning: passing argument 2 of ‘pop’ from incompatible pointer type
char_stack_interface.c: In function ‘top_char’:
char_stack_interface.c:43: warning: passing argument 2 of ‘top’ from incompatible pointer type

This is my code:

char_stack_interface.h:

#ifndef _CHAR_STACK_INTERFACE_H
#define _CHAR_STACK_INTERFACE_H

#include "stack.h"

extern status push_char(stack *p_s, char  c);
extern status pop_char (stack *p_s, char *p_c);
extern status top_char (stack *p_s, char *p_c);

#endif

stack.h:

#ifndef _STACK_H
#define _STACK_H

#include "globals.h"

ABSTRACT_TYPE(stack);

extern status init_stack (stack *p_S);
extern bool   empty_stack(stack *p_S);
extern status push       (stack *p_S , generic_ptr data);
extern status pop        (stack *p_S , generic_ptr *p_data);
extern status top        (stack *p_S , generic_ptr *p_data);

#endif

char_stack_interface.c:

#include <stdio.h>
#include <stdlib.h>
#include "char_stack_interface.h"
#include "stack.h"

status push_char(stack *p_s, char c)
{
    char *p_c = NULL;
    p_c = (char *) malloc(sizeof(char));

    if (p_c == NULL)
        return ERROR;

    *p_c = c;

    if (push(p_s, p_c) == ERROR) {
        free(p_c);
        return ERROR;
    }

    return OK;
}
status pop_char (stack *p_s, char *p_c)
{
    char *p_data;

    if (pop(p_s, p_data) == ERROR)
        return ERROR;

    *p_c = *p_data;

    free(p_data);

    return OK;
}
status top_char (stack *p_s, char *p_c)
{
    char *p_data;

    if (top(p_s, &p_data) == ERROR)
        return ERROR;

    *p_c = *p_data;

    return OK;
}

Answer 1

Well whatever the generic_ptr type is, obviously the compiler is not able to automatically cast your ‘char *’ type into generic ptr type. Try doing an explicit case of your second arg to pop and top e.g.:

pop(p_s, (generic_ptr)p_data)