gcc -O

gcc -O option flags

gcc -O sets the compiler's optimization level.

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

Syntax

$ gcc -Olevel [options] [source files] [object files] [-o output file]

Example

myfile.c:

// myfile.c
#include <stdio.h>

void main()
{
    printf("Program run\n");
}

Build myfile.c on terminal and run the output file myfile:

$ gcc -O myfile.c -o myfile
$ ./myfile
Program run
$