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What GCC options should be set to have GCC as strict as possible? (and I do mean as strict as possible) I'm writing in C89 and want my code to be ANSI/ISO compliant.
I'd recommend using:
-Wall -Wextra -std=c89 -pedantic -Wmissing-prototypes -Wstrict-prototypes \
-Wold-style-definition
You should compile with -O as well as -g as some warnings are only available when the optimizer is used (actually, I usually use -O3 for spotting the problems). You might prefer -std=gnu89 as that disables fewer extensions in the libraries. OTOH, if you're coding to strict ANSI C89, maybe you want them disabled. The -ansi option is equivalent to -std=c89 but not quite as explicit or flexible.
The missing prototypes warns you about functions which are used (or external functions defined) without a prototype in scope. The strict prototypes means you can't use 'empty parentheses' for function declarations or definitions (or function pointers); you either need (void) or the correct argument list. The old style definition spots K&R style function definitions, such as:
int old_style(a, b) int a; double b; { ... }
If you're lucky, you won't need to worry about that. I'm not so lucky at work, and I can't use strict prototypes, much to my chagrin, because there are too many sloppy function pointers around.
See also: What is the best command-line tool to clean up code
This set of options is pretty good:
-Wall -Wextra -ansi -pedantic
You'll have to read the documentation to see if there are any extra warnings getting left out by that combination.
You should be warned that strict C89 doesn't include support for // style comments, and there are some pretty serious restrictions on the number of significant characters in the names of objects with external linkage.
来源：https://stackoverflow.com/questions/8946797/gcc-options-for-strictest-c-code