【C语言】C tips

1. How to solve warning: cast to pointer from integer of different size and vice versa:

#include <stdio.h>

int main() {
    void *p = NULL;
    int a = 3;
    p = (void *)a;
    a = (int)p;

    printf("%ld\n", p);
    printf("%ld\n", a);

    return 0;
}

The above code has the following warnings when compiling:

/tmp/0pubXc3fmS.c: In function 'main':
/tmp/0pubXc3fmS.c:7:9: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
    7 |     p = (void *)a;
      |         ^
/tmp/0pubXc3fmS.c:8:9: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
    8 |     a = (int)p;
      |         ^
/tmp/0pubXc3fmS.o

Converting pointer/data to (unsigned) long before casting to required data types can eliminate this warning: (intptr_t works the same)

#include <stdio.h>

int main() {
    void *p = NULL;
    int a = 3;
    p = (void *)(long)a;
    a = (int)(long)p;

    printf("%ld\n", p);
    printf("%ld\n", a);

    return 0;
}

2.