build_project_makefile.rst

Build a project using Makefile with Conan MakeDeps

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

We'll use Make as build system, so you should get it 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/makefile/makedeps/logger

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

.
├── Makefile
├── conanfile.txt
└── src
    └── main.cpp

This project contains a basic Makefile including the spdlog variable dependency and the source code for the logger program in main.cpp.

Let's have a look at the main.cpp file, it only prints a quote said by Corin, but uses spdlog::info method for it.

#include <cstdlib>
#include "spdlog/spdlog.h"


int main(void) {
    spdlog::info("To be a Cimmerian warrior, you must have both cunning and balance as well as speed and strength.");
    return EXIT_SUCCESS;
}

The Makefile specifies that logger is the expected executable and that it should be linked to the spdlog and fmt libraries. To simplify the usage, we use global variables to store the paths, flags and libraries.

ROOT_DIR:=$(shell dirname $(realpath $(firstword $(MAKEFILE_LIST))))
SRC_FOLDER    = $(ROOT_DIR)/src
BUILD_FOLDER  = $(ROOT_DIR)/build

include $(BUILD_FOLDER)/conandeps.mk

CXXFLAGS      += $(CONAN_CXXFLAGS) -std=c++11
CPPFLAGS      += $(addprefix -I, $(CONAN_INCLUDE_DIRS))
CPPFLAGS      += $(addprefix -D, $(CONAN_DEFINES))
LDFLAGS       += $(addprefix -L, $(CONAN_LIB_DIRS))
LDLIBS        += $(addprefix -l, $(CONAN_LIBS))
LDLIBS        += $(addprefix -l, $(CONAN_SYSTEM_LIBS))
EXELINKFLAGS  += $(CONAN_EXELINKFLAGS)


all:
    $(CXX) $(SRC_FOLDER)/main.cpp $(CPPFLAGS) $(CXXFLAGS) $(LDFLAGS) $(LDLIBS) $(EXELINKFLAGS) -o $(BUILD_FOLDER)/logger

The conanfile.txt looks simple as it just installs the spdlog package and uses MakeDeps to build our project.

[requires]
spdlog/1.12.0

[generators]
MakeDeps

In this case, we will use :ref:`MakeDeps<conan_tools_gnu_makedeps>` to generate information about where the spdlog library files are installed thanks to the makedeps.mk file and using a conanbuild[.sh|.bat] file that describes the compilation environment.

We will use Conan to install spdlog library, generate a dependency file for Makefile, for find spdlog and fmt by make.

Building on Linux and macOS

First, we should install some requirements. On Linux you need to have make package installed, its package name should vary according to the Linux distribution.

For this example, we will not consider a specific Conan profile, but spdlog 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 spdlog 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 conanfile.txt --output-folder=build --build=missing

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

└── logger
    ├── Makefile
    ├── build
    │   ├── conanbuild.sh
    │   ├── conanbuildenv-release-armv8.sh
    │   ├── conandeps.mk
    │   ├── conanrun.sh
    │   ├── conanrunenv-release-armv8.sh
    │   ├── deactivate_conanbuild.sh
    │   ├── deactivate_conanbuildenv-release-armv8.sh
    │   └── deactivate_conanrun.sh
    ├── conandeps.mk
    ├── conanfile.txt
    ├── 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 spdlog is installed, now we can load the script conanbuild.sh.

source conanbuild.sh

The conanbuild.sh is a default file generated by the :ref:`VirtualBuildEnv<conan_tools_env_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 not affect our build right now because we don't have any other toolchain generator, but it will be useful in the next examples.

Then, finally, we can build the project to generate the logger application. Now we run the make command, which will consume the Makefile.

make

The make command will read the Makefile and first, include conandeps.mk, loading all variables that we need to find spdlog and fmt. Then, it will append the CXXFLAGS, CPPFLAGS, LDFLAGS, LDLIBS and EXELINKFLAGS variables with the information provided by conandeps.mk. Finally, it will invoke the compiler, then, build the main.cpp, generating the executable logger in the same folder.

./logger
To be a Cimmerian warrior, you must have both cunning and balance as well as speed and strength.

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