Re: Link errors

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From: Paul G. Tobey [eMVP] (ptobey)
Date: 09/02/04 

Date: Thu, 2 Sep 2004 14:44:36 -0700

C code *compiled for Windows CE*, not for the x86 emulator, right?

No, that's not true. C++ decorates the function names of things that it
sees declared so that linking is type-safe. That is, C++ can distinguish
between

int X( int a );

and

int X( float b );

In fact, it *has* to be able to do this to allow function overloading. If
you have an external C function that you are trying to declare, you *must*
wrap it with extern 'C', or C++ will see the declaration, modify the name it
is expecting to find, and your link will fail.

Most well-designed C libraries will do the right thing and wrap their
declarations in the header files so that they can be used from either C or
C++, but maybe that's not the case here. You'd do that something like this:

#ifdef __cplusplus
extern 'C'
{
#endif

<declarations here>

#ifdef __cplusplus
}
#endif

If the header files for this library don't have that, we've found the
problem and you may want to do something like:

extern 'C'
{
    #include <libraryheaderfile.h>
}

rather than what you probably have:

#include <libraryheaderfile.h>

Paul T.

"Pat Young" <PatYoung@discussions.microsoft.com> wrote in message
news:B89F5797-A2CA-46B5-9C80-00CB860EFFB6@microsoft.com...
> The processor is Intel Celeron. The lib herder files are c code. The
> library
> is C code library for x86 processor.
>
> But I noiced that all exapmle code from the vendor are C code. I believe
> that eVC++ is used for C++ code. The test application that I created is
> C++
> code (.cpp). I thought that I could directly use the c library without
> any
> changes or adding any extra code for calling C library functions in C++.
> Is
> it true?
>
> Pat
>
> "Paul G. Tobey [eMVP]" wrote:
>
>> I'd say that the library doesn't contain the function you are looking for
>> if
>> case 1 didn't work. Are you compiling your code as C++ and is the
>> library a
>> C library? Maybe name mangling is the problem. This library *is* for
>> the
>> right processor, right?
>>
>> Paul T.
>>
>> "Pat Young" <PatYoung@discussions.microsoft.com> wrote in message
>> news:4C104D0C-0383-48B0-B9EA-F55E2FFA9A31@microsoft.com...
>> > It still got the link errors even though changes were made based on
>> > suggestions from both Michael and Paul. Below are some test cases I
>> > did:
>> >
>> > Case 1:
>> > Object/library modules:
>> > mil.lib
>> >
>> > Additional library path:
>> > C:\Program Files\MIL for WinCE\Mil\Lib
>> >
>> > Error
>> > WinCETest002.obj : error LNK2019: unresolved external symbol
>> > __imp__RemoteMappFree referenced in function _WinMain
>> >
>> >
>> > Case 2:
>> > Object/library modules:
>> > mil.lib
>> >
>> > Additional library path:
>> > "C:\Program Files\MIL for WinCE\Mil\Lib"
>> >
>> > Error
>> > LINK : fatal error LNK1104: cannot open file 'mil.lib'
>> >
>> > case 3:
>> > Object/library modules:
>> > C:\Program Files\MIL for WinCE\Mil\Lib\mil.lib
>> >
>> > Additional library path:
>> > "C:\Program Files\MIL for WinCE\Mil\Lib"
>> >
>> > Error
>> > LINK : fatal error LNK1104: cannot open file 'C:\Program.obj'
>> >
>> > Case 4:
>> > Object/library modules:
>> >
>> > Additional library path:
>> > "C:\Program Files\MIL for WinCE\Mil\Lib\mil.lib"
>> >
>> > Error
>> > LINK : fatal error LNK1104: cannot open file 'Files\MIL.obj'
>> >
>> > Case 5:
>> > Object/library modules:
>> >
>> > Additional library path:
>> > C:\Program Files\MIL for WinCE\Mil\Lib\mil.lib
>> >
>> > Error
>> > WinCETest002.obj : error LNK2019: unresolved external symbol
>> > __imp__RemoteMappFree referenced in function _WinMain
>> >
>> > Case 6:
>> > Object/library modules:
>> > C:\Program Files\MIL for WinCE\Mil\Lib\mil.lib
>> >
>> > Additional library path:
>> >
>> > Error
>> > LINK : fatal error LNK1104: cannot open file 'C:\Program.obj'
>> >
>> > Case 7:
>> > Object/library modules:
>> > "C:\Program Files\MIL for WinCE\Mil\Lib\mil.lib"
>> >
>> > Additional library path:
>> > "C:\Program Files\MIL for WinCE\Mil\Lib"
>> >
>> > Error
>> > LINK : fatal error LNK1104: cannot open file 'Files\MIL.obj'
>> >
>> > Please see if there is anything else that I need to fix to build it
>> > correctly. Thanks.
>> >
>> > Pat
>> >
>> > "Paul G. Tobey [eMVP]" wrote:
>> >
>> >> And, although you specify the lib *path*, unless you specify the lib
>> >> *name*,
>> >> the library won't necessarily be added to the link. The library
>> >> developer
>> >> can arrange to make the library get included automatically, but it's
>> >> not
>> >> necessarily true that he did that...
>> >>
>> >> Paul T.
>> >>
>> >> "Michael J. Salamone [eMVP]" <mikesa#at#entrek#dot#com> wrote in
>> >> message
>> >> news:OLd6KuPkEHA.3456@TK2MSFTNGP12.phx.gbl...
>> >> > If specifying a full path, and it has spaces, you probably need to
>> >> > quote
>> >> > it.
>> >> >
>> >> > You shouldn't modify Library Directories for this. You should use,
>> >> > in
>> >> > Project Settings Link Tab, "dditional library path" (in the Input
>> >> > category).
>> >> > You probably need to quote it there, too. And, if you didn't quote
>> >> > it
>> >> > in
>> >> > Library Directories, that might be why it didn't find it in that
>> >> > case.
>> >> > In
>> >> > any case, undo whatever you did in Library Directories.
>> >> >
>> >> > I'm assuming your unresolved should be resolved by your mil.lib,
>> >> > correct?
>> >> > --
>> >> >
>> >> > Michael Salamone [eMVP]
>> >> > Entrek Software, Inc.
>> >> > www.entrek.com
>> >> >
>> >> >
>> >> >
>> >> > "Pat Young" <PatYoung@discussions.microsoft.com> wrote in message
>> >> > news:7D59BC16-3589-4C18-BE6A-743FD4689DF3@microsoft.com...
>> >> >> Hi,
>> >> >>
>> >> >> I am new to the eVC++. My development enviroment is the eVC++ 4.0
>> >> >> with
>> >> > sp2,
>> >> >> Windows XP and a third party device SDK.
>> >> >>
>> >> >> When I try to build a test application for a connected device, a
>> >> >> link
>> >> > error
>> >> >> 2019 "unresolved external symbol" occured even though the lib path
>> >> >> was
>> >> >> put
>> >> > on
>> >> >> the top of lib directories for the device platform.
>> >> >> Tools->Options...->Directories->Library files and the required
>> >> >> library
>> >> >> mil.lib was specified on the Object/library modules.
>> >> >>
>> >> >> Why did not the lib path take effect while linking?
>> >> >>
>> >> >> After the full path of the lib file was specified such as
>> >> >> C:\Program
>> >> >> Files\MIL for WinCE\Mil\Lib\mil.lib on the Object/library modules
>> >> >> and
>> >> > rebuilt
>> >> >> it, a new link error 1104 occured and followed by "cannot open file
>> >> >> 'C:\Program.obj'". What was wrong?
>> >> >>
>> >> >> Thanks in advance.
>> >> >>
>> >> >> Pat
>> >> >
>> >> >
>> >>
>> >>
>> >>
>>
>>
>>

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