C++ Program to Copy Strings

Introduction

Copying strings is a fundamental operation in C++ programming, involving the duplication of data from one string variable to another. This operation can be performed using various methods in C++, including the use of standard string functions, character arrays, or modern C++ techniques.

In this article, you will learn how to copy strings in C++ through multiple examples and methods. Discover the differences between using traditional character arrays and the more modern string class provided by the C++ Standard Library, and see how these techniques apply in practical programming scenarios.

Copying Strings Using the std::string Class

Direct Assignment

1. Initialize a string variable with a given value.

2. Copy the string to another string variable using the assignment operator.

   cpp Copy

   #include <iostream>
   #include <string>
   
   int main() {
       std::string original = "Hello, world!";
       std::string copy = original;
   
       std::cout << "Original: " << original << std::endl;
       std::cout << "Copy: " << copy << std::endl;
   
       return 0;
   }
   

   This example demonstrates how original string is directly assigned to copy. The output shows that both strings contain the same value, proving that the copy was successful.

Using the copy() Method

1. Use the copy() method from the std::string class to copy characters into a character array.

2. Specify the number of characters to copy and the starting position.

   cpp Copy

   #include <iostream>
   #include <string>
   
   int main() {
       std::string original = "Hello, world!";
       char buffer[20];
   
       original.copy(buffer, original.length(), 0);
       buffer[original.length()] = '\0';  // Null-terminate the character array
   
       std::cout << "Buffer contains: " << buffer << std::endl;
   
       return 0;
   }
   

   In this snippet, copy() is used to transfer characters from original to buffer. The buffer is then null-terminated to ensure that it represents a proper C-style string.

Copying Strings Using Character Arrays

Using strcpy()

1. Include the <cstring> header for string manipulation functions.

2. Use the strcpy() function to copy the contents from one character array to another.

   cpp Copy

   #include <iostream>
   #include <cstring>  // For strcpy
   
   int main() {
       char original[] = "Hello, world!";
       char copy[50];
   
       strcpy(copy, original);
       std::cout << "Original: " << original << std::endl;
       std::cout << "Copy: " << copy << std::endl;
   
       return 0;
   }
   

   The strcpy() function copies the string from original to copy including the terminating null character automatically.

Using a Manual Loop

1. Copy each character from the source to the destination manually using a loop.

2. Ensure to null-terminate the destination array after copying all characters.

   cpp Copy

   #include <iostream>
   
   int main() {
       char original[] = "Hello, world!";
       char copy[50];
       int i;
   
       for(i = 0; original[i] != '\0'; i++) {
           copy[i] = original[i];
       }
       copy[i] = '\0';  // Null-terminate the array
   
       std::cout << "Original: " << original << std::endl;
       std::cout << "Copy: " << copy << std::endl;
   
       return 0;
   }
   

   This code manually iterates through original and copies each character to copy. The loop stops when it encounters the null character, which it then adds to the end of copy.

Conclusion

With multiple ways to copy strings in C++, choose the method that best fits the scenario and the data structures being used. The std::string class provides a flexible and safe way to handle strings in modern C++, while traditional character arrays offer a more manual approach, often used where fine control over memory and performance is crucial. Apply these techniques to ensure that your C++ programs handle string duplication efficiently and correctly.