std::to_string
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< cpp | string | basic string
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Defined in header
<string>
std::string to_string( int value );
(1)
(since C++11)
std::string to_string( long value );
(2)
(since C++11)
std::string to_string( long long value );
(3)
(since C++11)
std::string to_string( unsigned value );
(4)
(since C++11)
std::string to_string( unsigned long value );
(5)
(since C++11)
std::string to_string( unsigned long long value );
(6)
(since C++11)
std::string to_string( float value );
(7)
(since C++11)
std::string to_string( double value );
(8)
(since C++11)
std::string to_string( long double value );
(9)
(since C++11)
Converts a numeric value to std::string .
Let buf be an internal to the conversion functions buffer, sufficiently large to contain the result of conversion.
1) Converts a signed integer to a string as if by std::sprintf (buf, "%d", value).
2) Converts a signed integer to a string as if by std::sprintf (buf, "%ld", value).
3) Converts a signed integer to a string as if by std::sprintf (buf, "%lld", value).
4) Converts an unsigned integer to a string as if by std::sprintf (buf, "%u", value).
5) Converts an unsigned integer to a string as if by std::sprintf (buf, "%lu", value).
6) Converts an unsigned integer to a string as if by std::sprintf (buf, "%llu", value).
7,8) Converts a floating point value to a string as if by std::sprintf (buf, "%f", value).
9) Converts a floating point value to a string as if by std::sprintf (buf, "%Lf", value).
(until C++26)1-9) Converts a numeric value to a string as if by std::format ("{}", value).
(since C++26)[edit] Parameters
value
-
a numeric value to convert
[edit] Return value
A string holding the converted value.
[edit] Exceptions
May throw std::bad_alloc from the std::string constructor.
[edit] Notes
- With floating point types
std::to_stringmay yield unexpected results as the number of significant digits in the returned string can be zero, see the example. - The return value may differ significantly from what
std::coutprints by default, see the example.
-
std::to_stringrelies on the current C locale for formatting purposes, and therefore concurrent calls tostd::to_stringfrom multiple threads may result in partial serialization of calls.- The results of overloads for integer types do not rely on the current C locale, and thus implementations generally avoid access to the current C locale in these overloads for both correctness and performance. However, such avoidance is not guaranteed by the standard.
C++17 provides std::to_chars as a higher-performance locale-independent alternative.
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_to_string |
202306L |
(C++26) | Redefining std::to_string in terms of std::format
|
[edit] Example
Run this code
#include <cstdio> #include <format> #include <initializer_list> #include <iostream> #include <string> #if __cpp_lib_to_string >= 202306L constexpr auto revision() { return " (post C++26)"; } #else constexpr auto revision() { return " (pre C++26)"; } #endif int main() { for (const double f : {1.23456789555555, 23.43, 1e-9, 1e40, 1e-40, 123456789.0}) { std::cout << "to_string:\t" << std::to_string(f) << revision() << '\n'; // Before C++26, the output of std::to_string matches std::printf. std::printf ("printf:\t\t%f\n", f); // As of C++26, the output of std::to_string matches std::format. std::cout << std::format ("format:\t\t{}\n", f); std::cout << "std::cout:\t" << f << "\n\n"; } }
Possible output:
to_string: 1.234568 (pre C++26) printf: 1.234568 format: 1.23456789555555 std::cout: 1.23457 to_string: 23.430000 (pre C++26) printf: 23.430000 format: 23.43 std::cout: 23.43 to_string: 0.000000 (pre C++26) printf: 0.000000 format: 1e-09 std::cout: 1e-09 to_string: 10000000000000000303786028427003666890752.000000 (pre C++26) printf: 10000000000000000303786028427003666890752.000000 format: 1e+40 std::cout: 1e+40 to_string: 0.000000 (pre C++26) printf: 0.000000 format: 1e-40 std::cout: 1e-40 to_string: 123456789.000000 (pre C++26) printf: 123456789.000000 format: 123456789 std::cout: 1.23457e+08