C++ <cstring>

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++ 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;
}

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:

Example:

// 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;
}

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.

• 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.