How to Convert String to Char Array in C++

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Jinku Hu Feb 02, 2024
C++ C++ String C++ Char
  1. Use std::basic_string::c_str Method to Convert String to Char Array
  2. Use std::vector Container to Convert String to Char Array
  3. Use Pointer Manipulation Operations to Convert String to Char Array
How to Convert String to Char Array in C++

This article introduces multiple methods for converting string data to char array.

Use std::basic_string::c_str Method to Convert String to Char Array

This version is the C++ way of solving the above problem. It uses the string class built-in method c_str which returns a pointer to a null-terminated char array.

#include <iostream>
#include <string>

using std::cin;
using std::cout;
using std::endl using std::string;

int main() {
  string tmp_string = "This will be converted to char*";
  auto c_string = tmp_string.c_str();

  cout << c_string << endl;
  return EXIT_SUCCESS;
}

Output:

This will be converted to char*

If you intend to modify data stored at the pointer returned by the c_str() method, first, you must copy the range to a different location with memmove function and then operate on the char string as follows:

#include <cstring>
#include <iostream>
#include <string>

using std::cin;
using std::cout;
using std::endl using std::string;

int main() {
  string tmp_string = "This will be converted to char*";

  char *c_string_copy = new char[tmp_string.length() + 1];
  memmove(c_string_copy, tmp_string.c_str(), tmp_string.length());

  /* do operations on c_string_copy here */

  cout << c_string_copy;
  delete[] c_string_copy;
  return EXIT_SUCCESS;
}

Note that, you can copy c_string data using various functions like: memcpy, memccpy, mempcpy, strcpy or strncpy, but bear in mind to read the manual pages and carefully consider their edge cases/bugs.

Use std::vector Container to Convert String to Char Array

Another way is to store characters from string into vector container and then use its powerful built-in methods to manipulate data safely.

#include <iostream>
#include <iterator>
#include <string>
#include <vector>

using std::cin;
using std::cout;
using std::endl;
using std::string;
using std::vector;

int main() {
  string tmp_string = "This will be converted to char*\n";

  vector<char> vec_str(tmp_string.begin(), tmp_string.end());
  std::copy(vec_str.begin(), vec_str.end(),
            std::ostream_iterator<char>(cout, ""));

  return EXIT_SUCCESS;
}

Use Pointer Manipulation Operations to Convert String to Char Array

In this version, we define a char pointer named tmp_ptr and assign the first character’s address in tmp_string to it.

#include <iostream>
#include <string>

using std::cin;
using std::cout;
using std::endl using std::string;

int main() {
  string tmp_string = "This will be converted to char*\n";
  string mod_string = "I've been overwritten";

  char *tmp_ptr = &tmp_string[0];
  cout << tmp_ptr;

  return EXIT_SUCCESS;
}

Remember though, modifying data at tmp_ptr would also alter the tmp_string value, which you can see by executing the following code sample:

#include <cstring>
#include <iostream>
#include <string>

using std::cin;
using std::cout;
using std::endl using std::string;

int main() {
  string tmp_string = "This will be converted to char*\n";
  string mod_string = "I've been overwritten";

  char *tmp_ptr = &tmp_string[0];
  memmove(tmp_ptr, mod_string.c_str(), mod_string.length());

  cout << tmp_string;
  return EXIT_SUCCESS;
}
Author: Jinku Hu
Jinku Hu avatar Jinku Hu avatar

Founder of DelftStack.com. Jinku has worked in the robotics and automotive industries for over 8 years. He sharpened his coding skills when he needed to do the automatic testing, data collection from remote servers and report creation from the endurance test. He is from an electrical/electronics engineering background but has expanded his interest to embedded electronics, embedded programming and front-/back-end programming.

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