G++ Compiler Options Guide | Generated by AI

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G++ is the GNU C++ compiler, part of the GCC (GNU Compiler Collection) suite. It transforms C++ source code into executable programs through compilation and linking. Understanding its options is essential for effective C++ development.

Basic Usage

The simplest g++ invocation compiles and links a program in one step:

g++ program.cpp -o program

This creates an executable named program from program.cpp.

Essential Options

Output Control

• -o <filename> — Specify output file name (without this, defaults to a.out)
• -c — Compile to object file only, don’t link (produces .o files)
• -S — Generate assembly code only (.s files)
• -E — Preprocess only, output to stdout

Language Standards

• -std=c++11, -std=c++14, -std=c++17, -std=c++20, -std=c++23 — Select C++ standard version
• -std=gnu++17 — Use GNU extensions with C++17

Warning Options

• -Wall — Enable most common warnings (doesn’t actually mean “all”)
• -Wextra — Additional warnings beyond -Wall
• -Wpedantic — Strict ISO C++ warnings
• -Werror — Treat warnings as errors
• -Wconversion — Warn about implicit conversions that may alter values
• -Wshadow — Warn when variables shadow others

Optimization Levels

• -O0 — No optimization (default, fastest compilation)
• -O1 or -O — Basic optimization
• -O2 — Recommended optimization for release builds
• -O3 — Aggressive optimization, may increase binary size
• -Os — Optimize for size
• -Ofast — -O3 plus non-standards-compliant optimizations
• -Og — Optimize but maintain debuggability

Debugging

• -g — Include debugging information (for gdb, lldb)
• -g3 — Maximum debugging info including macro definitions
• -ggdb — Debugging info specifically for GDB

Include Paths and Libraries

Headers

• -I<directory> — Add directory to include search path
• -isystem <directory> — Add system header directory (suppresses warnings from these headers)

Libraries

• -L<directory> — Add directory to library search path
• -l<library> — Link against library (e.g., -lm for math library)
• -static — Link libraries statically instead of dynamically
• -shared — Create a shared library

Example:

g++ app.cpp -I./include -L./lib -lmylib -o app

Preprocessor Options

• -D<macro> — Define preprocessor macro (e.g., -DDEBUG)
• -D<macro>=<value> — Define macro with value
• -U<macro> — Undefine macro
• -include <file> — Include file before processing source

Code Generation

• -fPIC — Generate position-independent code (required for shared libraries)
• -march=<arch> — Generate code for specific architecture (e.g., -march=native)
• -mtune=<cpu> — Optimize for specific CPU without limiting compatibility
• -m32 / -m64 — Generate 32-bit or 64-bit code
• -pthread — Enable POSIX thread support

Analysis and Safety

• -fsanitize=address — Enable AddressSanitizer (detects memory errors)
• -fsanitize=undefined — Enable UndefinedBehaviorSanitizer
• -fsanitize=thread — Enable ThreadSanitizer (race condition detection)
• -fstack-protector-strong — Stack buffer overflow protection
• -D_FORTIFY_SOURCE=2 — Runtime buffer overflow protection

Practical Compilation Patterns

Debug Build:

g++ -std=c++17 -Wall -Wextra -g -Og program.cpp -o program_debug

Release Build:

g++ -std=c++17 -Wall -Wextra -O2 -DNDEBUG program.cpp -o program

Multiple Files:

# Compile separately
g++ -c -std=c++17 -Wall file1.cpp -o file1.o
g++ -c -std=c++17 -Wall file2.cpp -o file2.o

# Link together
g++ file1.o file2.o -o program

With Sanitizers (during development):

g++ -std=c++17 -g -fsanitize=address,undefined program.cpp -o program

Advanced Options

• -v — Verbose output showing all compilation steps
• -save-temps — Keep intermediate files (preprocessed, assembly)
• -pipe — Use pipes instead of temporary files (faster compilation)
• -fno-exceptions — Disable C++ exception handling
• -fno-rtti — Disable runtime type information
• -flto — Enable link-time optimization

Getting Help

• g++ --help — Show brief help
• g++ --help=warnings — Show warning options
• man g++ — Full manual page

The most common combination for everyday development is something like -std=c++17 -Wall -Wextra -O2 for release builds and -std=c++17 -Wall -Wextra -g -Og for debug builds.

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