<cstring> Reference

The <cstring> library in C++ provides a set of functions for manipulating C-style strings. These functions are essential for tasks such as string length calculation, copying, concatenation, comparison, and tokenization. Understanding these functions is crucial for any C++ programmer dealing with text data.

Introduction

C-style strings are arrays of characters terminated by the null character ('\0'). The <cstring> library offers a variety of functions to perform operations on these strings efficiently. In this tutorial, we will explore some of the most commonly used functions: strlen, strcpy, strcat, strcmp, strncpy, memcpy, memset, and strtok.

Core Content

1. strlen

The strlen function calculates the length of a C-style string (excluding the null terminator).

Syntax

1size_t strlen(const char *str);

• Parameters: A pointer to the C-style string.
• Return Value: The number of characters in the string.

Example

1#include <iostream>
2#include <cstring>
3 
4int main() {
5    const char str[] = "Hello, World!";
6    std::cout << "Length of "" << str << "" is " << strlen(str) << std::endl;
7    return 0;
8}

3. strcat

The strcat function appends a string to the end of another string.

Syntax

1char *strcat(char *dest, const char *src);

• Parameters:
  • dest: Pointer to the destination array where the content is to be appended.
  • src: C-style string to append.
• Return Value: A pointer to the destination string.

Example

1#include <iostream>
2#include <cstring>
3 
4int main() {
5    char dest[50] = "Hello, ";
6    const char src[] = "World!";
7    strcat(dest, src);
8    std::cout << "Concatenated string: " << dest << std::endl;
9    return 0;
10}

5. strncpy

The strncpy function copies up to a specified number of characters from one string to another.

Syntax

1char *strncpy(char *dest, const char *src, size_t n);

• Parameters:
  • dest: Pointer to the destination array where the content is to be copied.
  • src: C-style string to copy.
  • n: Maximum number of characters to copy.
• Return Value: A pointer to the destination string.

Example

1#include <iostream>
2#include <cstring>
3 
4int main() {
5    char dest[50];
6    const char src[] = "Hello, World!";
7    strncpy(dest, src, 5);
8    dest[5] = ''; // Null-terminate the string manually
9    std::cout << "Copied string: " << dest << std::endl;
10    return 0;
11}

7. memset

The memset function sets a specified number of bytes to a given value.

Syntax

1void *memset(void *str, int c, size_t n);

• Parameters:
  • str: Pointer to the block of memory to fill.
  • c: Value to set. The value is passed as an int, but the function fills the block of memory using the unsigned char conversion of this value.
  • n: Number of bytes to be set to the value.
• Return Value: A pointer to the memory area str.

Example

1#include <iostream>
2#include <cstring>
3 
4int main() {
5    char str[50];
6    memset(str, 'A', 10); // Set first 10 bytes to 'A'
7    str[10] = ''; // Null-terminate the string manually
8    std::cout << "String after memset: " << str << std::endl;
9    return 0;
10}

Practical Example

Let's create a simple program that reads a sentence from the user and counts the number of words using strtok.

1#include <iostream>
2#include <cstring>
3 
4int main() {
5    const int max_length = 100;
6    char sentence[max_length];
7    std::cout << "Enter a sentence: ";
8    std::cin.getline(sentence, max_length);
9    const char *delim = " 	";
10    char *token = strtok(sentence, delim);
11    int word_count = 0;
12    while (token != NULL) {
13        ++word_count;
14        token = strtok(NULL, delim);
15    }
16    std::cout << "Number of words: " << word_count << std::endl;
17    return 0;
18}

Summary

What's Next?

Now that you have a solid understanding of the <cstring> library, it's time to explore date and time manipulation with the <ctime> library. This will allow you to work with dates, times, and perform various time-related operations in your C++ programs.