GCC: compilation process..

gcc -Iproj/src myfile.c -o myfile
gcc -c myfile.c "compile without linking
gcc -D DEBUG myfile.c -o myfile
gcc -glevel  "level=0,1,3,null
"gcc -l links with a library file.
"gcc -L looks in directory for library files. "Link -l with library name without the lib prefix and the .a or .so extensions
gcc myfile.c -o myfile
gcc -Wall  "enable all warnings..

gcc

-I -L -l -D -g -O -o -Wall

about the -0 option.. ref to the following table..

Set the compiler's optimization level.

option	optimization level	execution time	code size	memory usage	compile time
-O0	optimization for compilation time (default)	+	+	-	-
-O1 or -O	optimization for code size and execution time	-	-	+	+
-O2	optimization more for code size and execution time	--		+	++
-O3	optimization more for code size and execution time	---		+	+++
-Os	optimization for code size		--		++
-Ofast	O3 with fast none accurate math calculations	---		+	+++

+increase ++increase more +++increase even more -reduce --reduce more ---reduce even more

some environmental variables used in gcc: for more, see here

LANG　　　　　　　　　　　　　　1
LC_CTYPE　　　　　　　　　　　　1
LC_MESSAGES　　　　　　　　　　1
LC_ALL　　　　　　　　　　　　　　1
TMPDIR　　　　　　　　　　　　　　1
GCC_COMPARE_DEBUG　　　　　　1
GCC_EXEC_PREFIX　　　　　　　　1
COMPILER_PATH　　　　　　　　　　1
LIBRARY_PATH　　　　　　　　　　1
CPATH　　　　　　　　　　　　　　1
C_INCLUDE_PATH　　　　　　　　　1
CPLUS_INCLUDE_PATH　　　　　　1
OBJC_INCLUDE_PATH　　　　　　1
DEPENDENCIES_OUTPUT　　　　　　1
SUNPRO_DEPENDENCIES　　　　　　1
SOURCE_DATE_EPOCH　　　　　　1

-----to ensure how a lib is generated, by:

objdump --debugging *.a/*.so

part 2:------original file ends, adding more gcc options-----

from here:

-v, -save-temps, -S, -c, -E, -Werror, -fPIC, -ansi, -funsigned-char, -pg. -Wextra, -Wfloat-equal, -pipe, -funroll-loops (code size up), -flto (e.g. inline opt)

@filename to specify options in file.

Note, from here and here, -march/-mtune is very powerful, specify different arch/tune mighe influence final code. And march is stronger than mtune, it enables generating code that may not be run other than the specified cpu.

gprof usage: -pg option used while compile & linking, then ./a.out then a file named gmon.out is generated. Then use gprof a.out gmon.out > gprof.txt generate a profile for human readable format of gprof.

valgrind tutorial is here.