Convert String to Char Array in C++

In C++, we usually represent text data using the std::string object. But in some cases, we may need to convert a std::string to a character array, the traditional C-style strings. In this article, we will learn how to convert the string to char array in C++.

Examples

Input: str = "geeksforgeeks"
Output: char arr[] = { 'g', 'e', 'e', 'k', 's', 'f', 'o', 'r', 'g', 'e', 'e', 'k', 's', '\0' };
Explanation: str is converted to character array.

Input: str = "abc"
Output: char arr[] = {'a', 'b', 'c', '\0'}
Explanation: str is converted to character array.

Following are the different ways to convert the string to char array in C++:

Using std::string::c_str() Method

To change std::string to char array, we can first use string::c_str() function to get the underlying character array that contains the string stored in std::string object. Then we can create a copy of this char array using strcpy() function. We can also use & (Address-of) operator to get the underlying character array by fetching the address of the first character.

Code Implementation

// C++ program to convert string to char array
// using string::c_str()
#include <bits/stdc++.h>
using namespace std;

int main() {
  
    // Assigning value to string s
    string str = "geeksforgeeks";

    int n = str.length();

    // declaring character array (+1 for null
  	// character)
    char arr[n + 1];

    // copying the contents of the string to
  	// char array
    strcpy(arr, str.c_str());
	
  	cout << "{ ";
  	for (int i = 0; i < n; i++)
      cout << arr[i] << ", ";
    cout << "}";
    return 0;
}

{ g, e, e, k, s, f, o, r, g, e, e, k, s, }

Time complexity: O(n), where n is the number of characters in a string.
Auxiliary Space: O(n)

Using std::copy() Method

In the above method, we have first fetched the underlying character array of std::string object. But we can also directly convert std::string to char array by using std::copy() function. This function works for both iterators and pointers so we can copy the std::string objects (uses iterator) directly to character array (uses pointers).

Syntax

copy(first, last, pos);

Parameters

• first: Iterator to the beginning of string object.
• last: Iterator to the position just after the end of the string object.
• pos: Pointer to the start of the character array

Code Implementation

// C++ Program for converting the string to 
// char array using std::copy()
#include <bits/stdc++.h>
using namespace std;

int main() {
    string str = "geeksforgeeks";
    int n = str.length();
  
    char arr[n + 1];
  
    // Specify the ranges
    auto first = str.begin();
    auto last = str.end();
  
    // Convert the string to char array
    copy(first, last, arr);
    
    // Null terminate the char array
    arr[n] = '\0';
    
    cout << "{ ";
  	for (int i = 0; i < n; i++)
      cout << arr[i] << ", ";
    cout << "}";
    return 0;
}

{ g, e, e, k, s, f, o, r, g, e, e, k, s, }

Time Complexity: O(n), where n is the length of the string.
Auxiliary Space: O(n)

Using Loops

To manually covert the string to char array, we can use any C++ loop to iterate through each element of the std::string and copy the character to the char array one by one.

Code Implementation

// C++ program to manually convert string to
// char array using a loop
#include <bits/stdc++.h>
using namespace std;

int main() {
    string str = "geeksforgeeks";
    int n = str.length();

    // Create a new array of chars to copy the
    // string
    char arr[n + 1];

    // Null terminate char array
    arr[n] = '\0';

  	// Copy each character of str to arr
    for (int i = 0; i < n; i++)
        arr[i] = str[i];

    cout << "{ ";
  	for (int i = 0; i < n; i++)
      cout << arr[i] << ", ";
    cout << "}";
    return 0;
}

{ g, e, e, k, s, f, o, r, g, e, e, k, s, }

Time Complexity: O(n), where n is the length of the string.
Auxiliary Space: O(n)