c - How do you allow spaces to be entered using scanf?

Question

Using the following code:

char *name = malloc(sizeof(char) + 256); 

printf("What is your name? ");
scanf("%s", name);

printf("Hello %s. Nice to meet you.
", name);

A user can enter their name but when they enter a name with a space like Lucas Aardvark, scanf() just cuts off everything after Lucas. How do I make scanf() allow spaces

Answer 1

People (and especially beginners) should never use scanf("%s") or gets() or any other functions that do not have buffer overflow protection, unless you know for certain that the input will always be of a specific format (and perhaps not even then).

Remember than scanf stands for "scan formatted" and there's precious little less formatted than user-entered data. It's ideal if you have total control of the input data format but generally unsuitable for user input.

Use fgets() (which has buffer overflow protection) to get your input into a string and sscanf() to evaluate it. Since you just want what the user entered without parsing, you don't really need sscanf() in this case anyway:

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

/* Maximum name size + 1. */

#define MAX_NAME_SZ 256

int main(int argC, char *argV[]) {
    /* Allocate memory and check if okay. */

    char *name = malloc(MAX_NAME_SZ);
    if (name == NULL) {
        printf("No memory
");
        return 1;
    }

    /* Ask user for name. */

    printf("What is your name? ");

    /* Get the name, with size limit. */

    fgets(name, MAX_NAME_SZ, stdin);

    /* Remove trailing newline, if there. */

    if ((strlen(name) > 0) && (name[strlen (name) - 1] == '
'))
        name[strlen (name) - 1] = '';

    /* Say hello. */

    printf("Hello %s. Nice to meet you.
", name);

    /* Free memory and exit. */

    free (name);
    return 0;
}