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String formatting without memory allocator

In bare matal systems, there is often the task of converting numbers into text and formatting them. The standard Rust functions like format!, write! etc. cannot be used in no_std environments because they require a memory allocator. The arrform! macro uses the standard library functions, but writes to a fixed length array which is alocated on the stack.

This crate is usable in no_std environments. This is a replacement for the format! macro, based on a fixed-size array allocated on the stack.


use arrform::{arrform, ArrForm};
let af = arrform!(64, "write some stuff {}: {:.2}", "foo", 42.3456);
assert_eq!("write some stuff foo: 42.35", af.as_str());

ArrForm struct as an alternative

The ArrForm struct provides more detailed error handling and supports multiple use of the same buffer. However, it is much more cumbersome to use and generates more syntactic noise.


The convenient option to format can cost a lot of storage space. On a Cortex M4 992 bytes of program code are needed additionally, if instead of a simple string a simple u32 number is embedded with the help of the macro. It becomes even more expensive if f32 numbers are output formatted (30,928 bytes additional). The program code used to determine these numbers can be found in the example directory.


Apache version 2.0 or Mit


A macro to format numers into text, based on a fixed-size array allocated on the stack


Generates formatted text in a buffer on the stack