{fmt} is an open-source formatting library that provides a safe replacement for the printf family of functions. Errors in format strings, which are a common source of vulnerabilities in C, are reported at compile time. Formatting of most standard types, including all containers, dates, and times is supported out-of-the-box. Also, {fmt} provides portable Unicode support on major operating systems with UTF-8 and char strings.

Usage

To use fmt in your project, add the following configurations to the respective files after you have gained access to a build2 package repository that contains it.

manifest

To make fmt available for import, add the following dependency to the manifest of each package in your project that requires it, adjusting the version constraint as appropriate.

depends: fmt ^12.1.0

buildfile

To import the contained library, use the following declaration in your buildfile.

import fmt = fmt%lib{fmt}

Note also that lib{fmt} provides build2 metadata that can be extracted with an immediate importation to describe its configuration.

fmt.has_header = [bool] (!$config.fmt.module_only)
fmt.has_module = [bool] $cxx.features.modules

C++ Usage

If $fmt.has_header == true, {fmt}'s headers can be included as follows:

#include <fmt/format.h>

If $fmt.has_module == true, {fmt}'s C++ module can imported via:

import fmt;

Configuration

C++20 Modules Support

{fmt}'s C++ module support can be enabled by setting:

config.cxx.features.modules = true

By default, the library supports both module import through import fmt; and traditional header inclusion through, eg., #include <fmt/format.h>. To enable this dual usage, all entities are attached to the global module via global module linkage (extern "C++"). This ensures compatibility between module and header-based consumption.

To enforce strict module usage, use:

config.fmt.module_only = true

In this mode, header access is disabled and all entities are exclusively provided through the C++ module. This results in full encapsulation within the module and avoids global module linkage.