Build a simple Autotools project using Conan

In this example, we are going to create a string formatter application that uses one of the most popular C++ libraries: fmt.

We’ll use Autotools as build system and pkg-config as a helper tool in this case, so you should get them installed on Linux and Mac before going forward with this example.

Please, first, clone the sources to recreate this project, you can find them in the examples2.0 repository on GitHub:

git clone https://github.com/conan-io/examples2.git
cd examples2/examples/tools/autotools/autotoolstoolchain/string_formatter

We start with a very simple C++ language project with the following structure:

.
├── configure.ac
├── Makefile.am
├── conanfile.txt
└── src
    └── main.cpp

This project contains a basic configure.ac <https://www.gnu.org/software/autoconf/manual/autoconf-2.60/html_node/Writing-configure_002eac.html>_ including the fmt pkg-config dependency and the source code for the string formatter program in main.cpp.

Let’s have a look at the main.cpp file, it only prints a simple message but uses fmt::print method for it.

main.cpp
#include <cstdlib>
#include <fmt/core.h>

int main() {
    fmt::print("{} - The C++ Package Manager!\n", "Conan");
    return EXIT_SUCCESS;
}

The configure.ac file checks for a C++ compiler using the AC_PROG_CXX macro and also checks for the fmt.pc pkg-config module using the PKG_CHECK_MODULES macro.

configure.ac
AC_INIT([stringformatter], [0.1.0])
AM_INIT_AUTOMAKE([1.10 -Wall no-define foreign])
AC_CONFIG_SRCDIR([src/main.cpp])
AC_CONFIG_FILES([Makefile])
PKG_CHECK_MODULES([fmt], [fmt])
AC_PROG_CXX
AC_OUTPUT

The Makefile.am specifies that string_formatter is the expected executable and that it should be linked to the fmt library.

Makefile.am
AUTOMAKE_OPTIONS = subdir-objects
ACLOCAL_AMFLAGS = ${ACLOCAL_FLAGS}

bin_PROGRAMS = string_formatter
string_formatter_SOURCES = src/main.cpp
string_formatter_CPPFLAGS = $(fmt_CFLAGS)
string_formatter_LDADD = $(fmt_LIBS)

The conanfile.txt looks simple as it just installs the fmt package and uses two generators to build our project.

conanfile.txt
[requires]
fmt/9.1.0

[generators]
AutotoolsToolchain
PkgConfigDeps

In this case, we will use PkgConfigDeps to generate information about where the fmt library files are installed thanks to the *.pc files and AutotoolsToolchain to pass build information to autotools using a conanbuild[.sh|.bat] file that describes the compilation environment.

We will use Conan to install fmt library, generate a toolchain for Autotools, and, .pc files for find fmt by pkg-config.

Building on Linux and macOS

First, we should install some requirements. On Linux you need to have automake , pkgconf and make packages installed, their packages names should vary according to the Linux distribution, but essentially, it should include all tools (aclocal, automake, autoconf and make) that you will need to build the following example.

For this example, we will not consider a specific Conan profile, but fmt is highly compatible with many different configurations. So it should work mostly with versions of GCC and Clang compiler.

As the first step, we should install all dependencies listed in the conanfile.txt. The command :ref: conan install<reference_commands_install> will not only install the fmt package, but also build it from sources in case your profile does not match with a pre-built binary in your remotes. Plus, it will provide these generators listed in the conanfile.txt

conan install . --build=missing

After running conan install command, we should have new files present in the string_formatter folder:

└── string_formatter
    ├── Makefile.am
    ├── conanautotoolstoolchain.sh
    ├── conanbuild.conf
    ├── conanbuild.sh
    ├── conanbuildenv-release-armv8.sh
    ├── conanfile.txt
    ├── conanrun.sh
    ├── conanrunenv-release-armv8.sh
    ├── configure.ac
    ├── deactivate_conanbuild.sh
    ├── deactivate_conanrun.sh
    ├── fmt-_fmt.pc
    ├── fmt.pc
    ├── run_example.sh
    └── src
        └── main.cpp

These files are the result of those generators listed in the conanfile.txt. Once all files needed to build the example are generated and fmt is installed, now we can load the script conanbuild.sh.

source conanbuild.sh

The conanbuild.sh is a default file generated by the VirtualBuildEnv and helps us to load other script files, so we don’t need to execute more manual steps to load each generator file. It will load conanautotoolstoolchain.sh, generated by AutotoolsToolchain, which defines environment variables according to our Conan profile, used when running conan install command. Those environment variables configured are related to the compiler and autotools, like CFLAGS, CPPFLAGS, LDFLAGS, and PKG_CONFIG_PATH.

As the next step, we can configure the project by running the following commands in sequence:

aclocal
automake --add-missing
autoconf
./configure

The aclocal command will read the file configure.ac and generate a new file named aclocal.m4, which contains macros needed by the automake. As the second step, the automake command will read the Makefile.am, and will generate the file Makefile.in. So the command autoconf will use those files and generate the configure file. Once we run configure, all environment variables will be consumed. The fmt.pc will be loaded at this step too, as autotools uses the custom PKG_CONFIG_PATH to find it.

Then, finally, we can build the project to generate the string formatter application. Now we run the make command, which will consume the Makefile generated by autotools.

make

The make command will read the Makefile and invoke the compiler, then, build the main.cpp, generating the executable string_formatter in the same folder.

./string_formatter
Conan - The C++ Package Manager!

The final output is the result of a new application, printing a message with the help of fmt library, and built by Autotools.