vermiiii0n/ffmt

C++ String formatter

Fast Format++

Intro

A simple and fast implementation for C++

Formatting into string is all it does.

Usage

Simple case

ffmt::format("Hello, {}!", "world");  // Hello, world!

Specify the index

ffmt::format("Hello, {1}! {0}", "world", "Hello"); // Hello, world!

Integer

ffmt::format("Hello, {1:9}! {0}", 123, 456); // Hello,       456! 123
ffmt::format("{:*^9}", 123); // ***123***
ffmt::format("{:*^9x}", 0xfff); // ***fff***
ffmt::format("{:0^9x}", 0xfff); // '000fff   ' //trailing 0s will change the value, so they are replaced with ' '
ffmt::format("{:>+09}", 123); // +00000123 // '+'/'-' signs are moved to the left when fill char is '0'

Float

ffmt::format("{}", 1.234567); // 1.234567
ffmt::format("{:.e}", 123.456); // 1.234567e2 Force to scientific notation
ffmt::format("{:.2}", 1234567890987654321); // 1.23e+18
ffmt::format("{:.2f}", 1234567890987654321.0); // 1234567890987654321.00 Force to float
ffmt::format("{:<05}", 1.23); // 1.2300  // in this case, it's safe to append 0s

General format string syntax

"{[index]:[fill][align][sign][padding].[precision][format]}"

• index: The index of the argument to format. It starts from 0.
• sign: + - Always show sign, - - no sign for non-negative(default).
• align:
  • > - Right align(default)
  • < - Left align
  • ^ - Center align.
• fill: The fill character. Default is space.
  • Anything not an Align symbol
  • nor a Sign symbol
  • nor .
  • nor int(except 0, 0 can be put before align or padding, output string will not affect the numeric value of the argument), format identifier may be used.
• padding: String at least takes this much space. Default is 0.
• precision: The precision of the argument. Default is 6.
• format: To specify format only, use {:.[format]} instead of {:[format]} or {[format]}, in {:f}, 'f' will be treated as fill char
  • b - Binary
  • o - Octal
  • d - Decimal
  • x - Hexadecimal
  • e - Scientific notation
  • f - Float
  • p - Pointer
  • default is decimal for int, auto for float(choose f or e based on length and padding settings).

To escape {, use "{{".

Benchmark

Versus fmt::format:

Pure string

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Benchmark            Time             CPU   Iterations
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ffmt_format        151 ns         87.6 ns      7854519
fmt_format         510 ns          298 ns      2352726

int

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Benchmark            Time             CPU   Iterations
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ffmt_format       1044 ns          444 ns      1675920
fmt_format        4192 ns         1703 ns       394154

float

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Benchmark            Time             CPU   Iterations
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ffmt_format        387 ns          193 ns      2618041
fmt_format        1329 ns          551 ns      1271178