Recommended gcc warning options for C
CGccCompiler ErrorsC Problem Overview
Other than -Wall what other warnings have people found useful?
http://gcc.gnu.org/onlinedocs/gcc-4.3.2/gcc/Warning-Options.html
C Solutions
Solution 1 - C
I routinely use:
gcc -m64 -std=c99 -pedantic -Wall -Wshadow -Wpointer-arith -Wcast-qual \
-Wstrict-prototypes -Wmissing-prototypes
This set catches a lot for people unused to it (people whose code I get to compile with those flags for the first time); it seldom gives me a problem (though -Wcast-qual is occasionally a nuisance).
Solution 2 - C
As of 2011-09-01, with gcc version 4.6.1
My current "development" alias
gcc -std=c89 -pedantic -Wall
-Wno-missing-braces -Wextra -Wno-missing-field-initializers -Wformat=2
-Wswitch-default -Wswitch-enum -Wcast-align -Wpointer-arith
-Wbad-function-cast -Wstrict-overflow=5 -Wstrict-prototypes -Winline
-Wundef -Wnested-externs -Wcast-qual -Wshadow -Wunreachable-code
-Wlogical-op -Wfloat-equal -Wstrict-aliasing=2 -Wredundant-decls
-Wold-style-definition -Werror
-ggdb3
-O0
-fno-omit-frame-pointer -ffloat-store -fno-common -fstrict-aliasing
-lm
The "release" alias
gcc -std=c89 -pedantic -O3 -DNDEBUG -flto -lm
As of 2009-11-03
"development" alias
gcc -Wall -Wextra -Wformat=2 -Wswitch-default -Wcast-align -Wpointer-arith
-Wbad-function-cast -Wstrict-prototypes -Winline -Wundef -Wnested-externs
-Wcast-qual -Wshadow -Wwrite-strings -Wconversion -Wunreachable-code
-Wstrict-aliasing=2 -ffloat-store -fno-common -fstrict-aliasing
-lm -std=c89 -pedantic -O0 -ggdb3 -pg --coverage
"release" alias
gcc -lm -std=c89 -pedantic -O3 -DNDEBUG --combine -fwhole-program -funroll-loops
Solution 3 - C
I started out with C++, so when I made the switch to learning C I made sure to be extra-anal:
-fmessage-length=0 -ansi -pedantic -std=c99 -Werror -Wall -Wextra -Wwrite-strings -Winit-self -Wcast-align -Wcast-qual -Wpointer-arith -Wstrict-aliasing -Wformat=2 -Wmissing-declarations -Wmissing-include-dirs -Wno-unused-parameter -Wuninitialized -Wold-style-definition -Wstrict-prototypes -Wmissing-prototypes
Solution 4 - C
I like -Werror. Keeps the code warning free.
Solution 5 - C
Get the manual for the GCC version you use, find all warning options available, and then deactivate only those for which you have a compelling reason to do so. (For example, non-modifiable third-party headers that would give you lots of warnings otherwise.) Document those reasons. (In the Makefile or wherever you set those options.) Review the settings at regular intervalls, and whenever you upgrade your compiler.
The compiler is your friend. Warnings are your friend. Give the compiler as much chance to tell you of potential problems as possible.
Solution 6 - C
I also use:
> -Wstrict-overflow=5
To catch those nasty bugs that may occur if I write code that relies on the overflow behaviour of integers.
And:
> -Wextra
Which enables some options that are nice to have as well. Most are for C++ though.
Solution 7 - C
I usually compile with "-W -Wall -ansi -pedantic" this helps ensure maximum quality and portability of the code.
Solution 8 - C
-pedantic -Wall -Wextra -Wno-write-strings -Wno-unused-parameter
For "Hurt me plenty" mode, I leave away the -Wno...
I like to have my code warning free, especially with C++. While C compiler warnings can often be ignored, many C++ warnings show fundamental defects in the source code.
Solution 9 - C
Right now I use:
-Wall -W -Wextra -Wconversion -Wshadow -Wcast-qual -Wwrite-strings -Werror
I took that list mostly from the book "An introduction to gcc" and then some from Ulrich Drepper recomendation about Defensive Programming (http://people.redhat.com/drepper/Defensive-slides.pdf).
But I don't have any science behind my list, it just felt like a good list.
/Johan
Note: I don't like those pedantic flags though....
Note: I think that -W and -Wextra are more or less the same thing.
Solution 10 - C
-pedantic-errors
Solution 11 - C
-Wfloat-equal, -Wshadow, -Wmissing-prototypes,
Solution 12 - C
-Wredundant-decls -Wnested-externs -Wstrict-prototypes -Wextra -Werror-implicit-function-declaration -Wunused -Wno-unused-value -Wreturn-type
Solution 13 - C
I generally just use
gcc -Wall -W -Wunused-parameter -Wmissing-declarations -Wstrict-prototypes -Wmissing-prototypes -Wsign-compare -Wconversion -Wshadow -Wcast-align -Wparentheses -Wsequence-point -Wdeclaration-after-statement -Wundef -Wpointer-arith -Wnested-externs -Wredundant-decls -Werror -Wdisabled-optimization -pedantic -funit-at-a-time -o
Solution 14 - C
The warning about uninitialized variables doesn't work unless you specify -O, so I include that in my list:
-g -O -Wall -Werror -Wextra -pedantic -std=c99
Solution 15 - C
-Wfatal-errors