Thread: fgets() and strlen() confusion

You can use scanf() super safely but it can be a pain in the ass.

Code:

#include <stdio.h>
#include <stdlib.h>
int main()
{
    char *data = NULL;
    char format[16];
    int length = 0;
    int convert = 0;
    puts("Please enter a string length.");
    convert = scanf("%i", &length);
    if (convert == 1 && length > 1)
    {
        data = malloc(1 + length);
        sprintf(format, "%%%ds", length);
    }
    else
    {
        fputs("Bad string length entered.\n",stderr);
        return 1;
    }

    printf("OK, enter your string (length = %d).\n", length);
    convert = scanf(format, data);
    if (convert == 1)
    {
        printf("Good job.\n\"%s\"\n", data);
    }
    else
    {
        fputs("There was a problem.\n",stderr);
    }
    free(data);
    data = NULL;

    return 0;
}

/*
Please enter a string length.
20
OK, enter your string (length = 20).
Low-calorie.beer
Good job.
"Low-calorie.beer"
*/

Basically you need to do that. I guess it could look worse, and I didn't check malloc(). Oh well. There's annoying things about scanf that won't be fixed, like not reading strings longer than one word.

[edit] It's not that scanf is a bad function that works poorly, but user input is frequently not formatted at all. Use scanf to read formatted files or something. It can be a lot of work to shoehorn this one way you know to get input into the program securely.[/edit]