When I try to build a program using Eclipse CDT
, I get the following:
/mingw/lib/libmingw32.a(main.o):main.c:(.text+0x106):
undefined reference to `WinMain@16
Why is that? And, how can I solve this issue?
ceclipseeclipse-cdt
When I try to build a program using Eclipse CDT
, I get the following:
/mingw/lib/libmingw32.a(main.o):main.c:(.text+0x106):
undefined reference to `WinMain@16
Why is that? And, how can I solve this issue?
Best Answer
This error occurs when the linker can't find
WinMain
function, so it is probably missing. In your case, you are probably missingmain
too.Consider the following Windows API-level program:
Now let's build it using GNU toolchain (i.e. g++), no special options. Here
gnuc
is just a batch file that I use for that. It only supplies options to make g++ more standard:This means that the linker by default produced a console subsystem executable. The subsystem value in the file header tells Windows what services the program requires. In this case, with console system, that the program requires a console window.
This also causes the command interpreter to wait for the program to complete.
Now let's build it with GUI subsystem, which just means that the program does not require a console window:
Hopefully that's OK so far, although the
-mwindows
flag is just semi-documented.Building without that semi-documented flag one would have to more specifically tell the linker which subsystem value one desires, and some Windows API import libraries will then in general have to be specified explicitly:
That worked fine, with the GNU toolchain.
But what about the Microsoft toolchain, i.e. Visual C++?
Well, building as a console subsystem executable works fine:
However, with Microsoft's toolchain building as GUI subsystem does not work by default:
Technically this is because Microsoft’s linker is non-standard by default for GUI subsystem. By default, when the subsystem is GUI, then Microsoft's linker uses a runtime library entry point, the function where the machine code execution starts, called
winMainCRTStartup
, that calls Microsoft's non-standardWinMain
instead of standardmain
.No big deal to fix that, though.
All you have to do is to tell Microsoft's linker which entry point to use, namely
mainCRTStartup
, which calls standardmain
:No problem, but very tedious. And so arcane and hidden that most Windows programmers, who mostly only use Microsoft’s non-standard-by-default tools, do not even know about it, and mistakenly think that a Windows GUI subsystem program “must” have non-standard
WinMain
instead of standardmain
. In passing, with C++0x Microsoft will have a problem with this, since the compiler must then advertize whether it's free-standing or hosted (when hosted it must support standardmain
).Anyway, that's the reason why g++ can complain about
WinMain
missing: it's a silly non-standard startup function that Microsoft's tools require by default for GUI subsystem programs.But as you can see above, g++ has no problem with standard
main
even for a GUI subsystem program.So what could be the problem?
Well, you are probably missing a
main
. And you probably have no (proper)WinMain
either! And then g++, after having searched formain
(no such), and for Microsoft's non-standardWinMain
(no such), reports that the latter is missing.Testing with an empty source: