What is the easiest way to pad a string with 0 to the left?

rust formatting string-formatting number-formatting
SeaEyeHay picture SeaEyeHay · May 22, 2018 · Viewed 9.4k times · Source

What is the easiest way to pad a string with 0 to the left so that

  • "110" = "00000110"

  • "11110000" = "11110000"

I have tried to use the format! macro but it only pads to the right with space:

format!("{:08}", string);

Answer

Shepmaster picture Shepmaster · May 22, 2018

The fmt module documentation describes all the formatting options:

Fill / Alignment

The fill character is provided normally in conjunction with the width parameter. This indicates that if the value being formatted is smaller than width some extra characters will be printed around it. The extra characters are specified by fill, and the alignment can be one of the following options:

  • < - the argument is left-aligned in width columns
  • ^ - the argument is center-aligned in width columns
  • > - the argument is right-aligned in width columns
assert_eq!("00000110", format!("{:0>8}", "110"));
//                                |||
//                                ||+-- width
//                                |+--- align
//                                +---- fill

See also:

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