How to Convert Int to Char Array in C++

1. Use std::sprintf Function to Convert int to Char Array in C++
2. Combine to_string() and c_str() Methods to Convert int to Char Array in C++
3. Use std::stringstream Class Methods to Convert int to Char Array in C++
4. Use std::to_chars Function to Convert int to Char Array in C++

This article will explain how to convert int to a char array (char*) using different methods.

In the following examples, we assume to store the output of conversion in-memory buffer, and for verification purposes, we’re going to output result with std::printf.

Use std::sprintf Function to Convert int to Char Array in C++

First, we need to allocate space to store a single int variable that we’re going to convert in a char buffer. Note that the following example is defining the maximum length MAX_DIGITS for integer data. To calculate the char buffer length, we add sizeof(char) because the sprintf function writes char string terminating \0 byte automatically at the destination. Thus we should mind allocating enough space for this buffer.

#include <iostream>

#define MAX_DIGITS 10

int main() {
  int number = 1234;
  char num_char[MAX_DIGITS + sizeof(char)];

  std::sprintf(num_char, "%d", number);
  std::printf("num_char: %s \n", num_char);

  return 0;
}

Output:

num_char: 1234

Note that calling sprintf with overlapping source and destination buffers (e.g. sprintf(buf, "%s some text to add", buf)) is not recommended as it has undefined behavior and will produce incorrect results depending on the compiler.

Combine to_string() and c_str() Methods to Convert int to Char Array in C++

This version utilizes std::string class methods to do the conversion, making it a far safer version than dealing with sprintf as shown in the previous example.

#include <iostream>

int main() {
  int number = 1234;

  std::string tmp = std::to_string(number);
  char const *num_char = tmp.c_str();

  printf("num_char: %s \n", num_char);

  return 0;
}

Use std::stringstream Class Methods to Convert int to Char Array in C++

This method is implemented using[the std::stringstream class. Namely, we create a temporary string-based stream where store int data, then return string object by the str method and finally call c_str to do the conversion.

#include <iostream>
#include <sstream>

int main() {
  int number = 1234;

  std::stringstream tmp;
  tmp << number;

  char const *num_char = tmp.str().c_str();
  printf("num_char: %s \n", num_char);
  ;

  return 0;
}

Use std::to_chars Function to Convert int to Char Array in C++

This version is a pure C++ style function added in C++17 and defined in header <charconv>. On the plus side, this method offers operations on ranges, which might be the most flexible solution in specific scenarios.

#include <charconv>
#include <iostream>

#define MAX_DIGITS 10

int main() {
  int number = 1234;
  char num_char[MAX_DIGITS + sizeof(char)];

  std::to_chars(num_char, num_char + MAX_DIGITS, number);
  std::printf("num_char: %s \n", num_char);

  return 0;
}