Pass dynamic memory

#include <stdlib.h>
#include <string.h>

/*
void GetMemory(char *p, int num)
{
    p = (char *)malloc(sizeof(char) * num);
}

int main()
{
    char *str = NULL;
    GetMemory(str, 100);
    // str is still NULL
    strcpy(str, "hello");
    return 0;
}
*/

void GetMemory(char **p, int num)
{
    *p = (char *)malloc(sizeof(char) * num);
}

int main()
{
    char *str = NULL;
    GetMemory(&str, 100);
    strcpy(str, "hello");
    return 0;
}