关于c编程的指针

Question

Please, if anyone know what's wrong in this tell me

#include"stdio.h"

void main() {
    int a = 10;
    int* p = &a;
    void** q = &p;
    printf("memory address=%d\n",(int*)*q);
}

Here is the compiler error:

warning: initialization from incompatible pointer type[-Wincompatible- pointer-types] void **q=&p;

ptr3.c:7:25: warning: format '%d' expects argument of type 'int', but argument 2 has type 'int ' [-Wformat=] printf("memory address=%d\\n",(int )*q); ~^ ~~~~~~~~ %ls

Is compiler wants to say that I cannot point a int type pointer using void pointer?

Answer 1

Is compiler wants to say that I cannot point a int type pointer using void pointer?

void ** q is type void ** while int * p is type int * . Hence this line: void ** q = &p; warrants a compiler warning as the types are not compatible.

If you typecast &p to a void * then the warning in your question will go away: void ** q = (void *)&p;

This line: printf("memory address=%d\\n",(int*)*q); should also cause a compiler warning because (int *)*q is type int * but the %d format specifier is expecting an int . If you use the format specifier %p then this warning will go away as well.