C++ String Conversion: Exploring std:from_chars in C++17 to C++26
The article outlines the evolution of `std::from_chars` in C++ from C++17 to C++26, highlighting its performance benefits for string-to-number conversions and its utility in applications like JSON parsing.
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The article discusses the introduction and evolution of the `std::from_chars` function in C++ from C++17 to C++26, which enhances string-to-number conversion capabilities. This function provides a low-level, high-performance alternative to older methods like `atoi` and `stringstream`, offering non-throwing, non-allocating, and memory-safe conversions without locale support. The API includes functions for both integral and floating-point types, returning a `from_chars_result` structure that indicates the success of the conversion and provides error information. Performance benchmarks show that `std::from_chars` is significantly faster than previous methods, with improvements noted in C++23 and upcoming features in C++26, such as constexpr support and simplified error checking. The article emphasizes the utility of `std::from_chars` for applications requiring efficient parsing, such as JSON and 3D model formats, and highlights the importance of compiler support across different platforms.
- `std::from_chars` offers a high-performance alternative for string-to-number conversions in C++.
- It provides detailed error reporting and is designed for both integral and floating-point types.
- Performance benchmarks indicate it is significantly faster than traditional methods like `atoi` and `stringstream`.
- C++23 introduces constexpr support, while C++26 will enhance error checking capabilities.
- The function is particularly useful for parsing tasks in applications like JSON and 3D modeling.
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9 comments const std::string str { "12345678901234" };
int value = 0;
std::from_chars(str.data(),str.data() + str.size(), value);
std::u8string_view chars{ u8"۱۲۳٤" };
int value;
enum { digit_base = 10 };
auto [ptr, ec] = std::from_chars(
chars.data(), chars.data() + chars.size(), value, digit_base);
return (ec == std::errc{}) ? value : -1;
That sounds like marketing BS, especially when most likely these functions just call into or are implemented nearly identically to the old C functions which are already going to "offers the best possible performance".
I did some benchmarks, and the new routines are blazing fast![...]around 4.5x faster than stoi, 2.2x faster than atoi and almost 50x faster than istringstream
Are you sure that wasn't because the compiler decided to optimise away the function directly? I can believe it being faster than istringstream, since that has a ton of additional overhead.
After all, the source is here if you want to look into the horse's mouth:
https://raw.githubusercontent.com/gcc-mirror/gcc/master/libs...
Not surprisingly, under all those layers of abstraction-hell, there's just a regular accumulation loop.
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