The -Wno-unused-variable switch usually does the trick. However, that is a very useful warning indeed if you care about these things in your project. It becomes annoying when GCC starts to warn you about things not in your code though. I would recommend you keeping the warning on, but use -isystem instead of -I for … Read more
-pthread tells the compiler to link in the pthread library as well as configure the compilation for threads. For example, the following shows the macros that get defined when the -pthread option gets used on the GCC package installed on my Ubuntu machine: $ gcc -pthread -E -dM test.c > dm.pthread.txt $ gcc -E -dM … Read more
I use it all the time in my coding. The -ansi flag is equivalent to -std=c89. As noted, it turns off some extensions of GCC. Adding -pedantic turns off more extensions and generates more warnings. For example, if you have a string literal longer than 509 characters, then -pedantic warns about that because it exceeds … Read more
Here are mine: -Wextra, -Wall: essential. -Wfloat-equal: useful because usually testing floating-point numbers for equality is bad. -Wundef: warn if an uninitialized identifier is evaluated in an #if directive. -Wshadow: warn whenever a local variable shadows another local variable, parameter or global variable or whenever a built-in function is shadowed. -Wpointer-arith: warn if anything depends … Read more
You can use the -Q –help=target options: gcc -march=native -Q –help=target … The -v option may also be of use. You can see the documentation on the –help option here.
In the early days of gcc (2.8 etc.) and in the times of egcs, and redhat 2.96 -O3 was quite buggy sometimes. But this is over a decade ago, and -O3 is not much different than other levels of optimizations (in buggyness). It does however tend to reveal cases where people rely on undefined behavior, … Read more