为什么我的代码会导致细分错误？

Question

When I run the following code, it shows "Segmentation fault (core dumped)". Could you help me figure out the mistake I made？

#include <stdio.h>

int str_len(char *s);

int main()
{

    int m;
    char a[] = "Hello, world";
    char *pa;
    *pa = a[0];
    m = str_len(pa);
    printf("The length of the string is %d.\n", m);
    return 0;

}

int str_len(char *s)
{

    int n;
    for (n = 0; *s != '\0'; s++)
            n++;
    return n;

}

Answer 1

Error in code : Assigning a character byte to a pointer. Technically it's ok, but the pointer does not contain a valid address. The error carries on and str_len receives that character thinking it is a byte. Trying to access that invalid address may cause the Segmentation Fault. pa char pointer is not initialized. Hence, *pa = a[0] is like trying to say address_memory_for_pointers = a[0] . Try running:

int m;
char a[] = "Hello, world";
char *pa = a;
m = str_len(pa);
printf("The length of the string is %d.\n", m);
return 0;

Answer 2

Using index with array name will always refer to address of particular element at that index.

*pa = a[0]; this will assign the pa to address of first element of array a , not the address of whole array. You should assign *pa = a; or *pa = &a; *pa = a; or *pa = &a; if you are intended to make pa to point the whole array.