C - strcspn() function

C strcspn() function - get the length of a complementary substring

The strcspn() function is used to find the first occurrence of a character in s1 that belongs to the set of characters that is specified by s2.

Syntax:

size_t strcspn(const char *s1, const char *s2);

Parameters:

Return value from strcspn()

• The strcspn() function returns the index of the first character found.
• Return the length of the string if no match found.
• No return value is reserved to indicate an error.

Examples: strcspn() function

Example 1: How strcspn() locates the index of specific characters in a given string?

This example demonstrates how strcspn() locates the index of specific characters in a given string. It searches for individual letters ("C", "L", "a", "g", and "U") within "C Language," outputting the index for each. This showcases how strcspn() can efficiently determine the position of various characters within a string.

Code:

#include <stdio.h>
#include <string.h>
 
#define SIZE 40
 
int main(void)
{
  char string1[SIZE] = "C Language";
  char ch;
  int index;
  printf("Original string: %s", string1);
  index = strcspn(string1, "C");
  printf("\n\nIndex of character 'C' in the said string is %d.",index);
  index = strcspn(string1, "L");
  printf("\n\nIndex of character 'L' in the said string is %d.",index);
  index = strcspn(string1, "a");
  printf("\n\nIndex of character 'a' in the said string is %d.",index);
  index = strcspn(string1, "g");
  printf("\n\nIndex of character 'g' in the said string is %d.",index);
  index = strcspn(string1, "U");
  printf("\n\nIndex of character 'U' in the said string is %d.",index);
}

Output:

Original string: C Language

Index of character 'C' in the said string is 0.

Index of character 'L' in the said string is 2.

Index of character 'a' in the said string is 3.

Index of character 'g' in the said string is 5.

Index of character 'U' in the said string is 10.

Example 2: Find position of the first vowel in a word

Code:

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

int main() {
    // Define a string to search within
    char text[] = "programming";
    // Define a set of vowels to search for
    char vowels[] = "aeiou";

    // Find the position of the first vowel
    int position = strcspn(text, vowels);

    // Print the position if a vowel is found
    if (position < strlen(text))
        printf("First vowel in \"%s\" found at position %d.\n", text, position);
    else
        printf("No vowels found in \"%s\".\n", text);

    return 0;
}

Output:

First vowel in "programming" found at position 2.

Explanation:

• Defines text with "programming" and vowels as "aeiou".
• strcspn() searches text for any character in vowels.
• Displays the position of the first vowel, if found.

Example 3: Find first forbidden character in password

Code:

#include <stdio.h>
#include <string.h>
int main() {
    // Password to check
    char password[] = "secure#pass";
    // Forbidden characters for passwords
    char forbidden[] = "#$%^&*";

    // Find the first occurrence of a forbidden character
    int position = strcspn(password, forbidden);

    // Print a warning if a forbidden character is found
    if (position < strlen(password))
        printf("Forbidden character found at position %d in \"%s\".\n", position, password);
    else
        printf("No forbidden characters found in \"%s\".\n", password);

    return 0;
}

Output:

Forbidden character found at position 6 in "secure#pass".

Explanation:

• Defines password with "secure#pass" and forbidden as "#$%^&*".
• Uses strcspn() to locate any forbidden characters in password.
• Alerts the user if a forbidden character is found by its position.

C Programming Code Editor:

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