Bug: 166632747

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  1. 0d5e3d8 Merge "Refresh Android.bp, cargo2android.json, TEST_MAPPING." by Joel Galenson · 5 weeks ago master
  2. d47ec7e Refresh Android.bp, cargo2android.json, TEST_MAPPING. by Joel Galenson · 7 weeks ago
  3. e32cb05 Enable tests am: e0a696b411 am: f7d05c7d87 am: f9f6a5235e by Jeff Vander Stoep · 3 months ago
  4. f9f6a52 Enable tests am: e0a696b411 am: f7d05c7d87 by Jeff Vander Stoep · 3 months ago
  5. f7d05c7 Enable tests am: e0a696b411 by Jeff Vander Stoep · 3 months ago


This crate provides fast functions for printing integer primitives to an io::Write or a fmt::Write. The implementation comes straight from libcore but avoids the performance penalty of going through fmt::Formatter.

See also dtoa for printing floating point primitives.

Version requirement: rustc 1.0+

itoa = "0.4"

Performance (lower is better)



use std::{fmt, io};

fn demo_itoa_write() -> io::Result<()> {
    // Write to a vector or other io::Write.
    let mut buf = Vec::new();
    itoa::write(&mut buf, 128u64)?;
    println!("{:?}", buf);

    // Write to a stack buffer.
    let mut bytes = [0u8; 20];
    let n = itoa::write(&mut bytes[..], 128u64)?;
    println!("{:?}", &bytes[..n]);


fn demo_itoa_fmt() -> fmt::Result {
    // Write to a string.
    let mut s = String::new();
    itoa::fmt(&mut s, 128u64)?;
    println!("{}", s);


The function signatures are:

fn write<W: io::Write, V: itoa::Integer>(writer: W, value: V) -> io::Result<usize>;

fn fmt<W: fmt::Write, V: itoa::Integer>(writer: W, value: V) -> fmt::Result;

where itoa::Integer is implemented for i8, u8, i16, u16, i32, u32, i64, u64, i128, u128, isize and usize. 128-bit integer support requires rustc 1.26+ and the i128 feature of this crate enabled.

The write function is only available when the std feature is enabled (default is enabled). The return value gives the number of bytes written.