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LICENSE | 4 years ago | |
README.md | 2 years ago | |
f_to_string.hpp | 4 years ago | |
to_string.hpp | 2 years ago |
README.md
constexpr-to-string
Requires C++14 or later.
Features:
- Convert any integral type to a string at compile-time
- Supports converting to bases 2 through 36
- No external dependencies
- Supports custom character types, e.g.
to_string<123, 10, wchar_t>
- C++20: Supports floating-point-to-string conversion with
f_to_string
How to use:
The file to_string.hpp
provides a to_string
utility, which may be used as below:
const char *number = to_string<2147483648999954564, 16>; // produces "1DCD65003B9A1884"
puts(number);
puts(to_string<-42>); // produces "-42"
puts(to_string<30, 2>); // produces "11110"
With to_string
, all that will be found in program disassembly are the resulting string literals, as if you wrote the strings yourself.
Try it on Compiler Explorer.
f_to_string.hpp
, requiring C++20, provides an f_to_string
utility for floating-point conversion:
puts(f_to_string<3.1415926>); // Defaults to 5-point precision: "3.14159"
puts(f_to_string<{3.1415926, 7}>); // Specify precision: "3.1415926"
How it works
C++14 greatly expanded the capabilities of compile-time code execution through constexpr
. In particular, it allows for non-trivial constructors to be constexpr
.
to_string
takes advantage of this by providing an object that converts a template-parameter integer to a string using a basic itoa
implementation in the constructor. Through an additional constexpr
member function, we can calculate the length of the resulting string; this can be used to size the object's string buffer for a perfect fit.
Beyond this, to_string
simply provides familiar member functions that allow for iteration and data access. The expansion of the capabilities of auto
in C++14 help make these definitions concise.
The floating-point implementation f_to_string
takes a similar approach, but requires C++20 as it needs a double_wrapper
object to capture the double
value. double
and float
cannot directly be template parameters as of C++20, and a non-type template parameter like the double_wrapper
structure was not allowed before C++20.