Explain string library functions with suitable examples in C

The C standard library provides several predefined functions for string manipulation in the string.h header file. These functions help perform operations like copying, comparing, concatenating, and searching strings efficiently.

Common String Functions

• strlen() − finds string length
• strcpy() − copies strings
• strcat() − concatenates strings
• strcmp() − compares strings
• strstr() − searches for substrings

The strlen() Function

The strlen() function returns the number of characters in a string, excluding the null terminator.

Syntax

size_t strlen(const char *str);

Example

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

int main() {
    char a[30] = "Hello";
    int l;
    l = strlen(a);
    printf("Length of the string = %d<br>", l);
    return 0;
}

Length of the string = 5

The strcpy() Function

The strcpy() function copies the source string into the destination string. The destination must have enough space to hold the source string.

Syntax

char *strcpy(char *destination, const char *source);

Example

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

int main() {
    char source[50] = "TutorialsPoint";
    char destination[50];
    strcpy(destination, source);
    printf("Source string: %s<br>", source);
    printf("Copied string: %s<br>", destination);
    return 0;
}

Source string: TutorialsPoint
Copied string: TutorialsPoint

The strcat() Function

The strcat() function concatenates (joins) two strings. It appends the source string to the end of the destination string.

Syntax

char *strcat(char *destination, const char *source);

Example

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

int main() {
    char a[50] = "Hello ";
    char b[20] = "World";
    strcat(a, b);
    printf("Concatenated string = %s<br>", a);
    return 0;
}

Concatenated string = Hello World

The strcmp() Function

The strcmp() function compares two strings lexicographically. It returns 0 if strings are equal, positive value if first string is greater, and negative value if first string is smaller.

Syntax

int strcmp(const char *str1, const char *str2);

Example

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

int main() {
    char str1[] = "apple";
    char str2[] = "ball";
    int result = strcmp(str1, str2);
    
    if (result == 0) {
        printf("%s is equal to %s<br>", str1, str2);
    } else if (result < 0) {
        printf("%s is less than %s<br>", str1, str2);
    } else {
        printf("%s is greater than %s<br>", str1, str2);
    }
    return 0;
}

apple is less than ball

The strstr() Function

The strstr() function searches for the first occurrence of a substring within a main string. It returns a pointer to the first occurrence or NULL if not found.

Syntax

char *strstr(const char *haystack, const char *needle);

Example

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

int main() {
    char mainStr[] = "Hello TutorialsPoint";
    char searchStr[] = "Tutorials";
    char *found = strstr(mainStr, searchStr);
    
    if (found) {
        printf("'%s' found at position %ld<br>", searchStr, found - mainStr);
    } else {
        printf("'%s' not found<br>", searchStr);
    }
    return 0;
}

'Tutorials' found at position 6

Conclusion

String library functions in C provide essential operations for string manipulation. These functions help handle copying, concatenation, comparison, and searching operations efficiently while maintaining proper memory management.