Cross-compiling is the process of compiling code on one platform, called the host, for execution on a different platform, called the target. This is commonly done in the realm of C++ development to compile code for embedded systems, mobile devices, or different operating systems.

To enable cross-compiling in C++, we need to set up a suitable build system that can generate the target executable or library. In this blog post, we will explore some popular build systems that support cross-compiling and discuss how to use them effectively.

1. CMake

CMake is a widely-used build system generator that allows for cross-compiling. It provides a platform-independent way to describe your build process and generate Makefiles, Ninja files, or build scripts for other build systems. CMake supports cross-compiling by specifying the target platform using the CMAKE_SYSTEM_NAME variable.

To use CMake for cross-compiling, you should first:

1. Install CMake on your development system.
2. Set the environment variable CC and CXX to point to the cross-compiler appropriate for your target.

Then create a CMakeLists.txt file in your project directory with the following contents:

cmake_minimum_required(VERSION 3.0)

project(MyProject)

set(CMAKE_SYSTEM_NAME Linux)  # Replace with your target platform name
set(CMAKE_C_COMPILER $ENV{CC})
set(CMAKE_CXX_COMPILER $ENV{CXX})

add_executable(my_executable main.cpp)

To generate the build files, run CMake with the path to the directory containing the CMakeLists.txt file. For example:

cmake -B build -S .

This will generate the necessary build files in the build directory. Finally, use your build system to build the project:

cmake --build build

Remember to replace Linux with the appropriate target platform name, such as Win32, Android, or iOS.

2. Make

Make is a widely-used build automation tool that can also be used for cross-compiling C++ projects. Make reads a Makefile that describes the dependencies and rules for building the project. To enable cross-compiling with Make, you typically need to set environment variables for the cross-compiler.

First, define the CC and CXX environment variables to point to the cross-compiler appropriate for your target platform:

export CC=/path/to/cross-compiler
export CXX=/path/to/cross-compiler-c++

Then, create a Makefile with the following contents:

CC := $(CC)
CXX := $(CXX)

all: my_executable

my_executable: main.cpp
    $(CXX) -o my_executable main.cpp

clean:
    rm -f my_executable

To build your project, run the make command:

make

3. Bazel

Bazel is a powerful build system that Google developed for handling large-scale software projects. It supports cross-compiling out of the box, making it an excellent choice for complex C++ projects.

To configure Bazel for cross-compiling, you need to create a .bazelrc file in your project directory with the following contents:

build --platforms=@local_config_platform//cpu:nacl
build --crosstool_top=@bazel_tools//tools/cpp:toolchain

Replace cpu:nacl with the appropriate target platform configuration, such as cpu:android, cpu:ios, or cpu:windows.

To build your project with Bazel, run the following command:

bazel build //my_executable:my_executable

Bazel will take care of invoking the appropriate cross-compiler and generating the target executable.

Conclusion

Cross-compiling C++ code involves configuring build systems to generate code for a different target platform. CMake, Make, and Bazel are popular build systems that support cross-compiling. By configuring them correctly, you can efficiently develop C++ applications for a wide variety of platforms.

Remember to set the appropriate environment variables for the cross-compiler and specify the target platform when necessary. With the right build system and setup, cross-compiling becomes a straightforward process, enabling you to deploy your C++ code on diverse platforms.

#cplusplus #crosscompiling