c++ - Do C++ formatting libraries generally fall back to *sprintf for numeric formatting?

Question

I am wondering whether "all" C++ formatting libraries eventually fall back to a *sprintf function to format numbers.

I am asking this because:

• Looking at the iostreams library that comes with Visual C++, I can see that numbers input into a stream will eventuall be formatted with sprintf_s.
• Boost.Format just uses the available iostreams library as far as I can tell.
• FastFormat eventually uses vsprintf to format a number.

So, are there iostreams implementations that do not use *sprintf and do the formatting themselves? Are there other formatting libraries that do not forward formatting of numbers to *sprintf family of functions?

I would appreciate answers in the form of:

• No: implementation XY uses ABC to format numbers
• Yes: all other (e.g. iostreams) implementations I know (X, Y, Z) also forward number formatting to stdio, because ...

Please avoid overly speculative answers.

Answer 1

Boost Spirit 不使用 *printf，从代码（real.hpp和int.hpp）和例如 ints 和 doubles 的基准中可以看出。

基准测试将 Boost Spirit Karma 的生成器与 Boost.Format 与 sprintf 和 std::stringstream 进行对比。只有 gcc 编译器的 sprintf 性能在该基准测试中才能接近。否则，Boost Spirit 无疑是赢家。

• http://www.boost.org/doc/libs/1_47_0/libs/spirit/doc/html/spirit/karma/performance_measurements/numeric_performance.html

Answer 2

不，例如{fmt} 库有自己的整数和浮点格式实现，这比sprintf. 以下是一个平台上双字符串格式基准 ( dtoa-benchmark ) 的结果：

如您所见，{fmt} 比sprintf这里快约 20 倍。

整数格式化也更快，但没有那么显着（在 Linux 和 macOS 上高达 6-7 倍）：

免责声明：我是 {fmt} 的作者。