A lightweight low-overhead library for processing printf-style format descriptions and arguments designed for the constrained environments of embedded systems.

News

• 15-Oct-2023: Implement the a and A hexadecimal floating point conversion specifiers.
• 18-Sep-2023: Add new microformat for a version smaller than tinyformat for extremely small platforms.
• 06-Sep-2023: Shrinking tinyformat for smaller code footprint.
• 29-Jun-2023: Add optional support (via config flag) for long long integers with the ll qualifier.
• 21-Jun-2023: Add tinyformat for an even smaller feature-reduced version of format for very small embedded systems (compiles to around 1,300 bytes of code for the atmega8 with AVR-GCC).
• March-2023: Tidyups in files and documentation.
• 10-Mar-2015: Release 1.2 now available.
• 05-Feb-2015: Add support for fixed-point numbers with the k conversion specifier.
• 06-Nov-2014: Add support for denormalized floating point numbers, for people who like really small numbers.
• 17-Mar-2014: Rounding bug fixed (Issue 7). Remaining work to get %g and %G conversion specifiers working properly.
• 20-Jan-2014: Bug in floating-point rounding code caused incorrect output for some values.
• 19-Aug-2013: Enhanced the e, E, f and F floating point conversions with the use of the ! flag to implement formatting to Engineering (x10³ etc) or SI (mega, micro, etc) units.
• 08-Aug-2013: Sincere apologies to those who have raised issues over the last couple of years. For some reason google did not notify me and I have only just found them. Hopefully now fixed.
• 19-Mar-2013: Added support for e, E, f, F, g and G floating point conversions.
• 19-mar-2013: After much consideration I have decided to change the way grouping is specified into a more natural form. This unfortunately breaks existing code. Sorry
• 16-Aug-2012: Added arbitrary numeric base conversions.
• 22-May-2012: Centre flag '^' uses '-' flag to bias left in %s conversions. It now also defaults to right bias in the same way that non-centred %s conversions are right-aligned by default.
• 07-Feb-2011: Added grouping specifiers to numeric conversions.
• 09-Dec-2010: Added support for ROM-located strings.
• 08-Dec-2010: Release 1.1 now available.
• 23-Nov-2010: Extended %c and added %C.
• 12-Nov-2010: Initial port to 8-bit AVR shows good size of about 2.5-2.8kB
• 11-Nov-2010: Added TestedPlatforms page
• 28-Sept-2010: Added support for length modifiers hh, j, z, t
• 23-June-2010: Release 1.0 now available.

Features

• Small code size (4kB code size without floating point formats, 8kB code with float support, compiled for ARM with GCC 12.2)
• Low system overheads (no large buffers)
• Fully re-entrant
• Supports most of ANSI C99 printf() format specifications (see below for exceptions) with many useful additional features

ANSI Exceptions

The following features from the ANSI C99 printf() format specifications are not supported in the current version of format

• Length modifier L (long double)

New Features

format brings new features to the world of printf, including

• b binary conversion for formatting unsigned values in base-2
• ! flag modifies the behaviour of the # flag in binary, octal and hexadecimal conversions to always add the prefix (the default is to drop the prefix for zero results)
• ! flag modifies the behaviour of the e, E, f and F floating point conversions to use engineering (for e/E) or SI (f/F) formatting
• Interspersing format specifications and arguments using a new continuation specifier (%")
• ^ flag centre-justifies conversion results if the field is wide enough to require padding
• c conversion treats precision as a repetition count.
• C conversion is same as c but gets character from format string itself.
• # flag with continuation and s conversions to select alternate ROM-based string pointers
• I and U conversions, together with a numeric base modifier, for arbitrary numeric base conversions (base 2-36)
• k fixed-point conversion specifier
• grouping modifier for formatting the output in useful ways

For examples of all these features please see testharness.c in the test folder.

Producing Output

format itself does not send any output characters to any device. Instead, it calls a consumer function, supplied by the caller, to process any output. A simple example would be a function to send the characters to a UART. A more advanced use might be sending characters to an LCD.

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