C++14 sprintf like string formatter with append mode. c+fmt is a library that use variadic templates and bounded C++ std::string to implement an snprintf and stringstream replacement.
- does not use varargs
- has a fixed stack frame
- implements SFINAE type boxing
- inline variadiac parameter packing
- accepts temporary references to std::string
- has a fixed stack frame and single ABI entry point
- appends to buffer to obviate the need for stringstream
- currently uses std::string for buffering
The follow types are handled:
- C strings - printf style C string formatting
- std::string - has a simpler argument format
- double (dtoa) - printf style double formatting
- double (hdtoa) - printf style double hex formatting
- integer (itoa) - printf style integer formatting
This code has been tested on:
- Linux with GCC 6.1.1 and libstdc++
- Linux with Clang 3.6.2 and libstdc++ or libc++
- macOS with Apple LLVM version 8.0.0 and libstdc++ or libc++
Linux 4.6.3 on Intel(R) Core(TM) i7-5557U CPU @ 3.10GHz
| method | format | time (ns) |
|---|---|---|
| snprintf | (%20s) | 93.250 |
| snprintf | (%20llu) | 103.247 |
| snprintf | (%7.5f) | 158.280 |
| snprintf | (%17.15f) | 240.950 |
| c+fmt | (%20s) | 66.340 |
| c+fmt | (%20llu) | 322.406 |
| c+fmt | (%7.5f) | 424.850 |
| c+fmt | (%17.15f) | 615.570 |
Note: during porting, the bigint code was simplified to remove
a custom allocation cache, to keep the code simple and thread
safe. c+bigint.h and c+dtoa.h can be further optimized.
| Name | Description |
|---|---|
| c+args.h | C++ variadia template argument type boxing and sprintf interface |
| c+bigint.h | C++ bigint (big integer) derived from netlib gdtoa |
| c+dtoa.h | C++ dtoa (double to ASCII) derived from netlib gdtoa |
| c+hdtoa.h | C++ hdtoa (double to Hex ASCII) derived from FreeBSD hdtoa |
| c+itoa.h | C++ itoa (integer to ASCII) derived from FreeBSD ultoa |
| c+fmt.h | C++ io_printf formatter derived from FreeBSD vfprintf |
c++ -Wall -O3 -std=c++14 test-fmt.cc -o test-fmt
c++ -Wall -O3 -std=c++14 bench-fmt.cc -o bench-fmt
or
c++ -Wall -Os -std=c++14 -stdlib=libc++ -fno-rtti -fno-exceptions test-fmt.cc -o test-fmt
c++ -Wall -Os -std=c++14 -stdlib=libc++ -fno-rtti -fno-exceptions bench-fmt.cc -o bench-fmt