CODEWITHSUNDEEP
cgcc
Sarath Babu
Sarath Babu

Reputation: 922

How to compile C program without any optimization

How can I compile a C program without undergoing any optimizations using gcc/g++?

Upvotes: 20

Views: 22086

Answers (5)

Brendan Gregg
Brendan Gregg

Reputation: 1015

Using -O0 is the closest I know of, however, unlike other replies, this does not mean zero optimizations. You can count the number of enabled optimizations for the different gcc optimization levels like this (this is gcc 4.8.2):

$ gcc -Q -O0 --help=optimizers | grep enabled | wc -l
52
$ gcc -Q -O1 --help=optimizers | grep enabled | wc -l
80
$ gcc -Q -O2 --help=optimizers | grep enabled | wc -l
110
$ gcc -Q -O3 --help=optimizers | grep enabled | wc -l
119

So at -O0, there are 52 optimizations enabled. I suppose one could disable them one-by-one, but I've never seen that done.

Note that the gcc man page says:

-O0 Reduce compilation time and make debugging produce the expected results.  This is the default.

It's not promising zero optimizations.

I'm not a gcc developer, but I would guess they would say that the -O0 optimizations have become so standard that they can barely be called optimizations anymore, rather, "standards". If that's true, it's a little confusing, since gcc still has them in the optimizers list. I also don't know the history well enough: perhaps for a prior version -O0 really did mean zero optimizations...

Upvotes: 24

demonkoryu
demonkoryu

Reputation: 1257

Use the compiler switch -O0.

Upvotes: 1

Brian McFarland
Brian McFarland

Reputation: 9422

Using gcc, pass in the flag: -O 0.

Upvotes: 1

Carl Norum
Carl Norum

Reputation: 224934

You shouldn't get any optimizations unless you ask for them via the -O flag. If you need to undo some defaults provided by your build system, -O0 will do that for you, as long as it's the last -O flag in the command line.

Upvotes: 6

Mysticial
Mysticial

Reputation: 471229

gcc main.c

or

g++ main.cpp

by default it doesn't do any optimizations. Only when you specify -O1, -O2, -O3, etc... does it do optimizations.

Or you can use the -O0 switch to make it explicit.

Upvotes: 20

Related Questions