String handling in C

String handling in C involves working with arrays of characters. Unlike higher-level languages that have built-in string types, C treats strings as arrays of characters terminated by a null character ('\0'). Here are some fundamental concepts and functions for handling strings in C:

Declaring and Initializing Strings in C

Static Initialization:

char str1[] = "Hello, World!";

This initializes a string with a null terminator automatically.

Dynamic Initialization:

char str2[20] = "Hello";

This creates a character array of size 20 and initializes it with the string “Hello”.

Common String Functions in C

The C Standard Library provides several functions to manipulate strings, declared in the string.h header.

strlen: Returns the length of the string (excluding the null terminator).

#include <string.h>
size_t len = strlen(str1);

strcpy: Copies one string to another.

char dest[50];
strcpy(dest, str1);

strncpy: Copies a specified number of characters from one string to another.

strncpy(dest, str2, 5);

strcat: Concatenates (appends) one string to another.

char str3[50] = "Hello";
strcat(str3, ", World!");

strncat: Concatenates a specified number of characters from one string to another.

strncat(str3, " How are you?", 5);

strcmp: Compares two strings lexicographically.

int result = strcmp(str1, str2);

strncmp: Compares a specified number of characters of two strings.

int result = strncmp(str1, str2, 5);

Example Program

Here’s a simple example demonstrating some of these functions:

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

int main() {
    char str1[20] = "Hello";
    char str2[20] = "World";
    char str3[40];

    // Concatenate str1 and str2
    strcpy(str3, str1);
    strcat(str3, " ");
    strcat(str3, str2);

    // Output the result
    printf("Concatenated String: %s\n", str3);

    // Length of str3
    printf("Length of str3: %lu\n", strlen(str3));

    // Compare str1 and str2
    int cmp = strcmp(str1, str2);
    if (cmp == 0) {
        printf("str1 and str2 are equal.\n");
    } else if (cmp < 0) {
        printf("str1 is less than str2.\n");
    } else {
        printf("str1 is greater than str2.\n");
    }

    return 0;
}

Key Points to Remember

• Always ensure your character arrays are large enough to hold the strings you work with, including the null terminator.
• Be cautious with functions like strcpy and strcat as they do not check for buffer overflows. Prefer their safer counterparts strncpy and strncat when dealing with unknown or potentially large input.
• Understand that strings in C are mutable, and you can manipulate individual characters within a string array directly.

By mastering these basic string handling functions, you can perform a wide range of text processing tasks in C.