What are string searching functions in C language?

String searching functions in C are built-in library functions that help locate specific characters, substrings, or patterns within strings. These functions are part of the standard C library (string.h) and provide efficient ways to search and analyze string content.

Syntax

#include <string.h>

char *strchr(const char *str, int c);
char *strrchr(const char *str, int c);
char *strpbrk(const char *s1, const char *s2);
size_t strspn(const char *s1, const char *s2);
size_t strcspn(const char *s1, const char *s2);
char *strtok(char *s1, const char *s2);
char *strtok_r(char *s1, const char *s2, char **saveptr);

String Searching Functions Overview

The following table lists the primary string searching functions available in C −

Example 1: Using strchr() Function

The strchr() function finds the first occurrence of a character in a string −

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

int main() {
    char *str1 = "Hello World";
    char *result;
    
    result = strchr(str1, 'l');
    if (result != NULL) {
        printf("First 'l' found at: %s
", result);
        printf("Position: %ld
", result - str1);
    } else {
        printf("Character not found
");
    }
    
    return 0;
}

First 'l' found at: llo World
Position: 2

Example 2: Using strpbrk() Function

The strpbrk() function finds the first occurrence of any character from a set −

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

int main() {
    char *str1 = "Hello World";
    char *result;
    
    result = strpbrk(str1, "aeiou");
    if (result != NULL) {
        printf("First vowel found: %c
", *result);
        printf("Remaining string: %s
", result);
    } else {
        printf("No vowels found
");
    }
    
    return 0;
}

First vowel found: e
Remaining string: ello World

Example 3: Using strtok() for String Tokenization

The strtok() function splits a string into tokens based on delimiters −

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

int main() {
    char str[] = "apple,banana,cherry";
    char *token;
    
    printf("Original string: %s
", str);
    printf("Tokens:
");
    
    token = strtok(str, ",");
    while (token != NULL) {
        printf("- %s
", token);
        token = strtok(NULL, ",");
    }
    
    return 0;
}

Original string: apple,banana,cherry
Tokens:
- apple
- banana
- cherry

Key Points

• All string searching functions require #include <string.h>
• strchr() and strrchr() return pointers to the found character or NULL
• strspn() and strcspn() return the count of matching/non-matching characters
• strtok() modifies the original string by inserting null terminators
• strtok_r() is the thread-safe version of strtok()

Conclusion

String searching functions in C provide powerful tools for locating characters, patterns, and splitting strings. These functions are essential for text processing and string manipulation tasks in C programming.