C++ <cstring>

Last Updated : 23 Jul, 2025

The <cstring> library is a part of the standard C++ library collection that provides the commonly used methods for C-Style string manipulation. It is inherited from the <string.h> library of C language.

We can import the <cstring> header file using #include preprocessor directive and all the <string.h> library function will be available to use in C++.

Syntax:

#include <cstring>

Example:

C++ 
// C++ program to demonstrate the use of <cstring> header
// File
#include <cstring>
#include <iostream>

using namespace std;

int main()
{
    // creating a test strings
    char name[20] = "David ";
    char last_name[20] = "Lauren";

    // initial strings
    cout << "Before Concatenation" << endl;
    cout << "\tName string: " << name << endl;
    cout << "\tString length: " << strlen(name) << endl;
  
    // using strcat() for concatenation
    strcat(name, last_name);

    // final strings
    cout << "After Concatenation" << endl;
    cout << "\tName string: " << name << endl;
    cout << "\tString length: " << strlen(name) << endl;

    return 0;
}

Output
Before Concatenation
    Name string: David 
    String length: 6
After Concatenation
    Name string: David Lauren
    String length: 12

<cstring> Functions

<cstring> header file contains some useful string manipulation functions. Some of these functions are listed below:

Function Name

Function Description

strlen()

Returns the length of the string.

strcpy()

Copy one string to another.

strncpy()

Copy first n characters of one string to another.

strcat()

Concatenates two strings.

strncat()

Concatenates first n characters of one string to another.

strcmp()

Compares two strings.

strncmp()

Compares first n characters of two strings.

strchr()

Find the first occurrence of the given character in the string.

strrchr()

Finds the last occurrence of the given characters in the string.

strstr()

Find the given substring in the string.

strcspn()

Returns the span of the source string not containing any character of the given string.

strspn()

Returns the span of the source string containing only the characters of the given string.

strpbrk()

Finds the first occurrence of any of the characters of the given string in the source string.

strtok()

Split the given string into tokens based on some character as a delimiter.

memset()

Initialize a block of memory with the given character.

memcmp()

Compares two blocks of memory.

memcpy()

Copy two blocks of memory.

memmove()

Moves two blocks of memory.

memchr()

Finds the given character in the block of memory.

Example:

C++ 
// C++ program to demonstrate the use of some common <cstring> library functions
#include <iostream>
#include <cstring>

using namespace std;

int main() {
    // initializing some strings
      char str1[20] = "Geeks";
      char str2[20] = "gfg";
      char str3[20] = "GeeksforGeeks";
  
      // using strlen()
      cout << "Str1 length: " << strlen(str1) << endl;
      
      // using strcat()
      cout << "str1 before concatenation: " << str1 << endl;
    strcat(str1, str2);
      cout << "str1 after concatenation: " << str1 << endl;
  
      // using strcpy()
      cout << "str1 before copy: " << str1 << endl;
      strcpy(str1, str3);
      cout << "str1 after copy: " << str1 << endl;
  
      return 0;
}

Output
Str1 length: 5
str1 before concatenation: Geeks
str1 after concatenation: Geeksgfg
str1 before copy: Geeksgfg
str1 after copy: GeeksforGeeks

Difference between <cstring> and <string>

Following are the differences between cstring and std::string which are defined inside cstring and string header files respectively.

Parameter

<cstring>

<string>

Definition<cstring> header file contains some useful functions that work on C-style strings.<string> header file imports the string class and its member and non-member functions to work on C++ style strings.
Implemented Data Type<cstring> functions work only on the array of characters type.<string> is a class that is used to create a string object to store characters and all its functions work only on string objects type.
Supporting LanguagesIt is a part of both C and C++.It's only the part of C++ only.
Memory ManagementMemory is managed manually and is usually of fixed size. Generally require less memory as compared to C++ Strings.Memory is managed automatically by the class. Require more memory for storing required data for better management.
Access and Operations' SpeedFaster access and operation speed due to simplicity.Generally slower because of automatic management.
  • Speed: If you need faster access speed and minimum memory usage, it is better to go with cstring as they are the simplest implementation of the string.
  • Convenience: If you prefer convenience and ease of access and operations, then it is better to go with the std::string.

Note: Methods of cstring library will not work on std::string data nor the methods of std::string will work on c style strings, but they can be easily converted another type easily using the methods mentioned here.

2. Difference between <cstring> and <string.h>

  • C language doesn't support cstring library. It is only part of standard C++ and is inherited from <string.h>. So if we want our program to run on both C and C++, we should use string.h header file.
  • When used in C++, <string.h> header file will import all its identifiers in the global namespace and maybe in the std namespace while <cstring> will import all its identifiers in the std namespace and maybe in the global namespace (depending on the compiler vendor).

3. Should I use <cstring> or <string.h> header file?

If we want our program to run both in C and C++ programming languages, then we should include <string.h> because the <cstring> header file is only part of C++, not C language.

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