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Please see the following code:

#include<stdio.h>
#include<stdlib.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<fcntl.h>
#include<unistd.h>


void destroy(int * p){
    if(p != NULL)
    {
        free(p);
        p = NULL;
    }
}
int main()
{
    int *p;
    p = (int*)malloc(sizeof(int)*5);
    p[0] = 1;
    p[1] = 2;
    destroy(&p);
    if(p == NULL)
        printf("AAAAAAAA\n");
    else
        printf("BBBBBBB\n");
    return 0;
}

Compile execution, output:

The P in the

BBBBBBB

function is a temporary variable that is passed into P. The pointing space is indeed free, but the assignment NULL is assigned to temporary variables.

Modify the Destroy function as follows, solve this problem.

void destroy(int ** p){
    if(*p != NULL)
    {
        free(*p);
        *p = NULL;
    }
}

Compile running output:

AAAAAA