scanf("%[^\n]s", str) Vs gets(str) in C with Examples

gets()

• gets is a more convenient method of reading a string of text containing whitespaces.
• Unlike scanf(), it does not skip whitespaces.
• It is used to read the input until it encounters a new line.

%[^\n]

• It is an edit conversion code.
• The edit conversion code %[^\n] can be used as an alternative to gets.
• C supports this format specification with scanf() function.
• This edit conversion code can be used to read a line containing characters like variables and even whitespaces.
• In general scanf() function with format specification like %s and specification with the field width in the form of %ws can read-only strings till the non-whitespace part.
• It means they cannot be used for reading a text containing more than one word, especially with Whitespaces.

Note: Both gets() & scanf() are does not perform bound checking.

Table of difference and similarities between gets() and %[^\n]

Example of gets()

#include <stdio.h>

int main() {
    char str[100];
   
    printf("Using gets:\n");
    printf("Enter a line of text: ");
    gets(str); // Reads a line of text, including white-space
    printf("You entered (gets): %s\n", str);
      return 0    
  }

Example of %[^\n]

#include <stdio.h>

int main() {

    char str[100];
  
      printf("Using scanf:\n");
    printf("Enter a line of text: ");
    scanf("%99[^\n]", str); // Reads a line of text, excluding white-space
      // %99 will stop buffer overflow
    printf("You entered (scanf): %s\n", str);

    return 0;
}

Safety Note: Both gets() and scanf() do not check array bounds, making them unsafe to use as they can lead to buffer overflow.

#include <stdio.h>

int main() {
    char name[10], sname[10];

    // Using gets()
    gets(name);
    printf("%s\n", name);

    // Using scanf() with %[^\n]
    scanf("%[^\n]", sname);
    printf("%s\n", sname);

    return 0;
}

INPUT

Geeks for Geeks
Geeks for Geeks

OUTPUT

Geeks for Geeks
Geeks for Geeks

Here, the complete line—including spaces—is read by both gets() and scanf("%[^\n]"), which then print it out. Nevertheless, if the input exceeds the allotted array size, undefined behavior may result from the absence of bound checking.