How to Use to_string in C++: Convert Numbers to Strings Easily

In C++, use the to_string function to convert numbers like int, float, or double into std::string. Simply call std::to_string(value) where value is the number you want to convert.

Syntax

The to_string function is used to convert numeric values to strings. It is part of the std namespace and works with types like int, long, float, double, and long long.

• std::to_string(value): Converts value to a std::string.
• value: A numeric variable or literal you want to convert.

cpp

std::string s = std::to_string(123);

Example

This example shows how to convert different numeric types to strings using std::to_string and print them.

cpp

#include <iostream>
#include <string>

int main() {
    int i = 42;
    float f = 3.14f;
    double d = 2.71828;

    std::string si = std::to_string(i);
    std::string sf = std::to_string(f);
    std::string sd = std::to_string(d);

    std::cout << "int to string: " << si << "\n";
    std::cout << "float to string: " << sf << "\n";
    std::cout << "double to string: " << sd << "\n";

    return 0;
}

Output

int to string: 42
float to string: 3.140000
double to string: 2.718280

Common Pitfalls

Some common mistakes when using to_string include:

• Not including the <string> header, which causes compilation errors.
• Expecting to_string to format floating-point numbers with fewer decimals; it defaults to 6 decimal places.
• Using to_string on non-numeric types, which is not supported.

To control floating-point formatting, use std::ostringstream instead.

cpp

/* Wrong: missing #include <string> */
// std::string s = to_string(10); // Error: to_string not found

/* Right: include string and use std::to_string */
#include <string>
std::string s = std::to_string(10);

Quick Reference

Type	Usage Example	Resulting String
int	std::to_string(123)	"123"
float	std::to_string(3.14f)	"3.140000"
double	std::to_string(2.71828)	"2.718280"
long long	std::to_string(1234567890123LL)	"1234567890123"

Key Takeaways

Use std::to_string(value) to convert numbers to strings easily in C++.

Include the header and use the std namespace for to_string.

to_string formats floating-point numbers with 6 decimal places by default.

to_string only works with numeric types, not custom or non-numeric types.

For custom formatting of numbers, consider using string streams instead.