Problems with limiting a string length in C

Question

I'm relatively new to coding and do not understand why I'm receiving an Exception thrown with a simple scanf.

char word[15];

printf("\nEnter a word: ");
scanf_s("%15s", word);

Answer 1

scanf_s requires a third argument, the sizeof the buffer:

scanf_s("%s", word, sizeof(word));

scanf_s can either be Microsoft-specific or the one defined by the C standard but which isn't mandatory to be implemented in every C implementation. Dependent on which one you use you either need to cast the sizeof() argument to unsigned(Microsoft implementation) or cast it to rsize_t (C standard).

Related:

• Difference between scanf and scanf_s
• String input using C scanf_s

Note that you also should check the return value of scanf_s.

if ( scanf_s("%s", word, (unsigned) sizeof(word)) != 1 )
{
    // error routine.
}

If you want to write portable code, use fgets() instead:

if ( !fgets(word, sizeof(word), stdin) )
{
   // error routine.
}

Answer 2

Strings

Strings in C are represented using an array of characters.

These arrays must be terminated using a null character \0, as the C standard library is written assuming you will be writing strings this way.

When you define the array char word[15] you are allocating enough memory to store 14 characters plus the null character.