Resources:

GCC Flags

Summary:


# Options I use
-Wall -Wextra -Werror -pedantic -std=c17 -Wformat=2 -Wformat-truncation -Werror=vla -Wundef -Wfloat-conversion -Wdouble-promotion -Wshadow -Wcast-align

# Warnings I disable
-Wno-unused-variable -Wno-unused-function -Wno-unused-parameter -Wno-missing-field-initializers -Wno-missing-braces

# Special behavior flags I use
-fno-strict-aliasing -fwrapv -fwrapv-pointer

# Debug flags
-O0 -g -DDEBUG

# Optimized flags
-O3 -march=native

# Other
-Icode/    # Add "code/" to include directories
-lm        # Link library "m"
-o blah    # Sets output file to "blah"

# Also: When using interfacing with Linux,
# you might need to define _POSIX_C_SOURCE
# or _GNU_SOURCE

Options I use:

-Wall: Enable a lot of warnings (but contrary to the name, not all)
-Wextra: Enable even more warnings
-Werror: Make the compilation fail if any warnings are generated
-pedantic: Create a warning if the code is not following the C standard (e.g. using gnu-extensions)
-std=c17: Specify the standard to follow (here: C17)
-Wformat=2: For e.g. printf / scanf, check the format strings against the provided function parameters and warn on mismatch
- When defining a custom variadic function which takes e.g. printf-style arguments, you can enable warnings by adding e.g. __attribute__((format(printf, 1, 2))) in front of the function definition
- Format: format(archetype, string-index, first-to-check)
-Wformat-truncation: For e.g. snprintf, warn if the output might be truncated
-Wundef: Warn if an undefined identifier is evaluated in an #if directive
-Wfloat-conversion: Warn about implicit conversions which reduce the precision of a real value (e.g. double -> float or float -> int)
-Wdouble-promotion: Warn about implicit conversion from float to double
-Wshadow: Warn if a variable or type shadows another.
-Wcast-align: Warn if casting a pointer requires a stricter alignment.

I used to use -Wsign-conversion:

Warn about implicit conversions which change the sign of an integer value
Causes lots of extra typing, and hasn't caught that many bugs for me
Not even libraries like the stb_-headers use this warning

Special behavior flags:

-fno-strict-aliasing: Disable the compiler optimization that two pointers of (almost all) differing types are always referring to different types. I don't like this behavior (of the C standard).
-fwrapv: Assume that signed arithmetic overlfwo wraps around using twos-complement. This is true for all architectures I care about.
-fwrapv-pointer: Same as above but for pointers.

Warnings I disable:

-Wno-unused-variable: Don't warn on unused variables
-Wno-unused-function: Don't warn on unused functions
-Wno-unused-parameter: Don't warn on unused function parameters
-Wno-missing-field-initializers: When initializing a struct, don't warn if an initializer of some field is missing (C standard mandates that a field without an initializer is implicitly set to 0)
-Wno-missing-braces: For nested struct / unions, don't warn if an initializer is not fully bracketed

Debug flags:

-O0: Disable optimizations
-g: Produce debugging information
-DDEBUG: Predefines the macro DEBUG to 1 (preprocessor can then check for debug/release builds using #ifdef DEBUG [...] #else [...] #endif)

Release flags:

-O3: Enable (most) optimizations
-march=native: Enable usage of instructions which are supported by the local machine