CFLAGSCXXFLAGS

CFLAGS and CXXFLAGS are conventional variables used in many build systems to specify options passed to the C and C++ compilers, respectively. They can be set as environment variables or defined in Makefiles, configure scripts, or build configurations. Their purpose is to influence how code is compiled, enabling optimization, debugging, warning control, include paths, macro definitions, and language standards.

Common contents include optimization and debugging switches (for example, -O2, -g), warning controls (-Wall, -Wextra), include directories (-I/path), macro definitions (-DNAME=VALUE), and language standards (-std=c11 for C, -std=c++17 for C++). They may also set architecture-specific flags (-march=native) or other compiler-specific options. In practice, CFLAGS affects the C compiler, while CXXFLAGS affects the C++ compiler, and they can be extended or overridden in a project’s build system.

In typical workflows, these variables are used by configure scripts and Makefiles to ensure consistent build options across targets and dependencies. They are widely supported by GCC and Clang, and in many projects they integrate with Autotools, Meson, CMake (as CMAKE_C_FLAGS and CMAKE_CXX_FLAGS), and other systems. On Windows, compilers like MSVC use different flag syntax, so CFLAGS/CXXFLAGS are most relevant in GCC/Clang environments or when using MinGW.

The combined term CFLAGSCXXFLAGS is not a universal standard; there is no single global variable with that name. Some projects may introduce a concatenated or project-specific variable, but the conventional and portable approach remains to use CFLAGS for C and CXXFLAGS for C++. When needed, a project can combine them at invocation time, but keeping them separate is generally clearer and more compatible.