'scanf_s' function doesn't work well in my C project

Question

My code:

#include <stdio.h>
int main() {
    char words[30];

    printf("Please typing text under 30 text!:");
    scanf_s("%s", words);

    printf("text: %s \n", words);

    return 0;
}

The error I get:

Missing integer argument to 'scanf_s' that corresponds to coversion specifier '2', 'scanf_s' not enough arguments passed for format string

Answer 1

Consider using fgets instead if you're simply reading everything into a string buffer. It's simpler and more portable:

char buffer[31]; // 1 extra for the zero terminator

printf("Please enter text with less than %zu characters\n", sizeof(buffer) - 1);

if (!fgets(buffer, (int)sizeof(buffer), stdin)) {
  puts("Failed to read input");
} else {
  // use input
}

Answer 2

As you can see in the scanf_s documentation :

specifiers each expect two arguments (the usual pointer and a value of type rsize_t indicating the size of the receiving array, which may be 1 when reading with a %c into a single char)

Ie for each argument you want scanf_s to parse, you need to pass its size .

Also scanf family return the number of arguments parsed, and you should check it to find out if it actually succeeded.

In your case change the scanf_s line to:

int n = scanf_s("%s", words, sizeof(words));
if (n != 1)
{
    // handle error
}

Note that sizeof(words) works here because it is an array allocated on the stack. If you allocate it as a pointer with malloc family you'll need to pass the right size (because then sizeof will return the size of the pointer itself).

Answer 3

Try this code:

#include <stdio.h>

    int main() {
      char words[30];
    
      printf("Please typing text under 30 text!:");
      scanf_s("%s", words,30);
    
      printf("text: %s \n", words);
    
      return 0;
    }

Also, you could put sizeof(words) instead of 30 as someone suggsted. (Note that this is only possible if you are working with static memory)

If you are using scan_s I think you want to ensure to read n symbols. Someone already suggested you to use fgets. Another possible solution is to use memcpy (you will read the exact bytes):

#include <stdio.h>

    int main() {
      char words[30];
      char words2[30];

    
      printf("Please typing text under 30 text!:");
      scanf("%s", words);
      memcpy(words2,words,sizeof(char)*30);
      words2[sizeof(char)*30]='\0';
      printf("text: %s \n", words2);
    
      return 0;
    }