Find the size of pointer in C

suppose char *str has some bytes(not malloced), how can i determine the size of *str without access to str itself?

~ >cat > test.c
#include <stdio.h>
int main()
{
    char * str = "abc";
    printf("%d\n",sizeof(str));
    return 0;
}
~ >gcc test.c
~ >./a.out
4
~ >