View Full Version : Ubiquitous "Undefined symbols for architecture x86_64" Error

gravity black
Dec 8, 2011, 06:19 PM
Hi all,

I'm trying to program a graph class using an adjacent list from an example in my C++ text book, and when I compile using this command:

g++ -o prog program.cpp

...I get the following error:

Undefined symbols for architecture x86_64:
"_main", referenced from:
start in crt1.10.6.o
ld: symbol(s) not found for architecture x86_64
collect2: ld returned 1 exit status

... what in the world does this mean? It may turn out to be an issue with my code, but I feel like it may be deeper than that, because I've gotten this same seemingly inexplicable error for several different projects, many of which were solved in different ways, and unfortunately completely by accident.

I read somewhere that it may have to do with whether I'm using 32 bit or 64 bit libraries, and that the tags -m32 or -m64 may need to be used, but I'm not sure if this applies here.

Mainly I just want to know what in the world the error is saying. I'm used to debugging compile-time errors that give a specific line in the code, etc., but I can't discern anything like that from this. Any ideas?

If it helps, I'm using a late 2008 Macbook with Intel Core 2 Duo, (so 64-bit), and I'm running OS X Lion (10.7.2), which I think is the latest version. Also, I'm using gcc version 4.2.1.

Dec 8, 2011, 08:12 PM
Does your program have a main() function in it? Is this program small? Can you post it?

Can you re-produce this error with a HelloWorld program? That might indicate whether your XCode install is messed up somehow.

gravity black
Dec 8, 2011, 08:39 PM
Ah, what a simple mistake. No, I did not have a main() function. Thanks for the help.

Anna is working
Aug 15, 2012, 09:09 AM

So actually what was your problem? I get same errors.

Aug 15, 2012, 12:38 PM

So actually what was your problem? I get same errors.

He already stated what the problem was. He did not have a main() function. A C++ program has to start somewhere, and it always starts by calling main(). So you have to provide a main() function in order for your program to run.