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This crate provides fast functions for printing floating-point primitives to an io::Write. The implementation is a straightforward Rust port of Milo Yip's C++ implementation dtoa.h. The original C++ code of each function is included in comments.

See also itoa for printing integer primitives.

Performance (lower is better)



extern crate dtoa;

// write to a vector or other io::Write
let mut buf = Vec::new();
dtoa::write(&mut buf, 2.71828f64)?;
println!("{:?}", buf);

// write to a stack buffer
let mut bytes = [b'\0'; 20];
let n = dtoa::write(&mut bytes[..], 2.71828f64)?;
println!("{:?}", &bytes[..n]);

The function signature is:

fn write<W: io::Write, V: dtoa::Floating>(writer: W, value: V) -> io::Result<()>

where dtoa::Floating is implemented for f32 and f64. The return value gives the number of bytes written.


Dtoa is available on crates.io. Use the following in Cargo.toml:

dtoa = "0.4"


Licensed under either of

at your option.


Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in dtoa by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.