String Handling in C: Common Functions and String Manipulation Techniques

In C, strings are stored as arrays of characters, terminated by a null character (‘\0’). Although C does not have a built-in string type, we can manipulate strings using a series of functions from the standard library. This article will introduce some common string handling functions and their usage techniques to help basic users better understand and utilize these tools.

1. String Definition

In C, a string is typically defined as an array of characters. For example:

char str[20] = "Hello, World!";

Here, <span>str</span> is an array containing 20 characters, which stores the string “Hello, World!”.

2. Common String Handling Functions

2.1 <span>strlen()</span>

<span>strlen()</span> function is used to calculate the length of a string (excluding the null terminator).

Example Code:

#include <stdio.h>
#include <string.h>
int main() {
    char str[] = "Hello, World!";
    size_t length = strlen(str);
    printf("The length of the string is: %zu\n", length);
    return 0;
}

Explanation:

• <span>strlen()</span> returns the length excluding the null character.
• Use <span>%zu</span> for formatting output of <span>size_t</span> type.

2.2 <span>strcpy()</span>

<span>strcpy()</span> function is used to copy one string to another location.

Example Code:

#include <stdio.h>
#include <string.h>
int main() {
    char source[] = "Hello, World!";
    char destination[50];
    strcpy(destination, source);
    printf("Copied string: %s\n", destination);
    return 0;
}

Explanation:

• Ensure the destination array has enough space to hold the source string and its null terminator.
• If the destination array is smaller than the source string, it will lead to a buffer overflow, which is very dangerous.

2.3 <span>strcat()</span>

<span>strcat()</span> function is used to concatenate two strings.

Example Code:

#include <stdio.h>
#include <string.h>
int main() {
    char str1[50] = "Hello";
    char str2[] = ", World!";
    strcat(str1, str2);
    printf("Concatenated string: %s\n", str1);
    return 0;
}

Explanation:

• <span>strcat()</span> appends the second argument to the first argument.
• Again, ensure the destination array has enough space to accommodate the result and the null terminator.

2.4 <span>strcmp()</span>

<span>strcmp()</span> function is used to compare two strings. It returns 0 if they are equal, a positive value if the first is greater than the second, and a negative value if it is less than the second.

Example Code:

#include <stdio.h>
#include <string.h>
int main() {
    char str1[] = "Apple";
    char str2[] = "Banana";
    int result = strcmp(str1, str2);
    if (result == 0) {
        printf("Strings are equal.\n");
    } else if (result > 0) {
        printf("%s is greater than %s.\n", str1, str2);
    } else {
        printf("%s is less than %s.\n", str1, str2);
    }
    return 0;
}

Explanation:

• The comparison is done character by character based on ASCII values.

2.5 <span>strchr()</span>

<span>strchr()</span> is used to find the first occurrence of a character in a given string and returns a pointer to that position. If not found, it returns NULL.

Example Code:

#include <stdio.h>
#include <string.h>
int main() {
    char str[] = "Hello, World!";
    char *ptr;
    ptr = strchr(str, 'W');
    if (ptr != NULL) {
        printf("'W' found at position: %ld\n", ptr - str + 1); // +1 for human-readable index
    } else {
        printf("'W' not found in the string.\n");
    }
    return 0;
}

Explanation:

• Pointer arithmetic is used to calculate the position of the character, noting to add an offset to make the output more human-readable (starting from 1).

Conclusion

The above introduces several commonly used string handling functions from the C standard library, including how to get length, copy, concatenate, compare, and find specific characters. These basic operations form an important foundation for more complex text processing capabilities in C. In actual programming, special attention should be paid to memory management and boundary conditions to avoid potential issues such as buffer overflows. I hope this article helps you better understand and use string operations in C.