char * as a reference in C

void set(char **buf)
{
    *buf = malloc(5*sizeof(char));
    // 1. don't assign the other string, copy it to the pointer, to avoid memory leaks, using string literal etc.
    // 2. you need to allocate a byte for the null terminator as well
    strcpy(*buf, "test");
}
 
char *str;
set(&str);
puts(str);
free(str);