CXXFLAGS

CXXFLAGS is an environment variable and make variable used to specify flags for the C++ compiler when building software. It is commonly used in Makefiles and build scripts to customize compilation options for C++ source files and is often read by the CXX variable, which holds the compiler command. CXXFLAGS is distinct from CFLAGS (used for C compilation) and CPPFLAGS (preprocessor options) and from LDFLAGS (linker options). In many projects, CXXFLAGS is combined with user-provided flags so developers can influence builds without editing the build system.

Common options included in CXXFLAGS cover optimization, debugging, warnings, standards, and compiler-specific features. Typical flags are -O2 or -O3 for optimization, -g for debugging symbols, -Wall and -Wextra (often with -Werror to treat warnings as errors), and -std=c++11, -std=c++14, -std=c++17, or -std=c++20 to select the C++ standard. Additional flags may enable or disable features, such as -fPIC for position-independent code, -fno-exceptions or -fno-rtti, and various -f options. Include directories and defines can also be supplied via -I and -D and are frequently included in CXXFLAGS. It is important to note that CXXFLAGS affects compilation only; linking is controlled by LDFLAGS or other link-related variables.

Usage example: CXXFLAGS="-O2 -g -Wall -std=c++17" make. On Windows with non-GNU toolchains, the exact flag names and usage may differ, as MSVC uses different options. In cross-platform or mixed environments, consider portability and consult project-specific build documentation.