Скачать или смотреть How to Pass CFLAGS and CXXFLAGS to CMake via Command Line

Learn how to easily set `CFLAGS` and `CXXFLAGS` in CMake without modifying the CMakeLists.txt file.
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Passing CFLAGS and CXXFLAGS to CMake via Command Line: A Quick Guide

Working on a project that utilizes CMake as its build system is a great choice among developers. However, there are times when you may need to pass specific compiler flags, such as CFLAGS and CXXFLAGS, without altering the project's CMakeLists.txt. This situation can get tricky, especially when working in an environment that restricts direct modifications to the configuration files. If you find yourself in this predicament while needing to debug your C+ + code, read on for a straightforward solution.

Understanding the Need for Flags

When compiling C or C+ + projects, compiler flags like -O0 and -DDEBUG help control optimization levels and define debug symbols. Specifically:

-O0: This flag disables optimizations, making debugging easier, as the code correlates closely with the source.

-DDEBUG: This flag defines the macro DEBUG, which can be used in the code to conditionally include debug-related statements.

The Problem

In the scenario you're dealing with, the project's CMake toolchain file only defines basic CFLAGS and CXXFLAGS for release builds. Since you require specific flags for debugging, attempting to set these flags through environment variables in the command line doesn't impact CMake as expected. For example, using:

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leaves both CFLAGS and CXXFLAGS empty when checking the output.

The Solution

Instead of trying to set the flags via environment variables, you can directly specify them through CMake command-line options. Here’s how to do it:

Step-by-Step Solution

Open your terminal where you want to configure your build.

Use the following command structure to pass the necessary flags:

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Breakdown of the Command

-DCMAKE_C_FLAGS="-O0 -DDEBUG": This sets the C compiler flags to include no optimization and enable debugging code.

-DCMAKE_CXX_FLAGS="-O0 -DDEBUG": This accomplishes the same for the C+ + compiler, ensuring your build aligns with debugging requirements.

-G 'Unix Makefiles': Specifies the generator to use, in this case, Unix Makefiles.

-DCMAKE_VERBOSE_MAKEFILE=ON: This option enables verbose output during the build process, which can be helpful for troubleshooting.

-DCMAKE_BUILD_TYPE=Debug: Specifies that you’re building a debug version of your project.

Example Usage

In the terminal, run the complete command to configure your project:

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Conclusion

In summary, when working with CMake and needing to specify compiler flags without modifying CMakeLists.txt, you can easily do so through the command line by using -DCMAKE_C_FLAGS and -DCMAKE_CXX_FLAGS. This method allows you to tailor the build process to your debugging needs seamlessly.

By following the steps outlined above, you can ensure that your project compiles with the appropriate flags, making your debugging experience smoother and more effective.

For any additional questions or clarifications, feel free to ask or consult the CMake documentation for further insights into custom configurations!