Question

Possible Duplicate:
Dynamic String Input – using scanf(“%as”)
strcmp with pointers not working in C

Is the following considered good code? Shouldn’t I have used malloc somewhere? I was able to compile this and it worked, but I feel like it shouldn’t have.

#include <stdio.h>

int main (void) {

    char *name;

    printf("Whats your name? ");
    scanf("%s", &name);
    printf("\nyour name is %s", &name);

    return 0;
}

What happens if I want to modify name? How would I go about doing so?

Edit: I am really just looking for the most efficient and correct way to do this using pointers. I am assuming malloc is necessary.

Answer 1

name is a pointer, and &name returns the address of the variable name, so the scanf is putting the name you enter into the pointer itself.

For example, if you enter ABC then the pointer will be 0x00434241 (if the CPU is little-endian) or 0x41434200 (if the CPU is big-endian), where 0x41 is the character code for ‘A’, 0x42 is the character code for ‘B’, etc.

You should allocate memory into which the entered name can be stored and then pass a pointer to it to scanf.

Here’s an example allocating on the stack:

#include <stdio.h>

#define MAX_NAME_LENGTH 256

int main (void) {

    char name[MAX_NAME_LENGTH];

    printf("Whats your name? ");
    scanf("%s", name);
    printf("\nyour name is %s", name);

    return 0;
}