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RE: Bug report: Compile with Microsoft and Intel compiler

From: Jerker Bäck
Subject: RE: Bug report: Compile with Microsoft and Intel compiler
Date: Fri, 29 Apr 2005 16:35:33 +0200

Eli Z:
> ??? Sorry, I'm mightily confused.  What do you mean by ``defined in 
> the runtime library''?  A library does not, AFAIK, include any 
> declarations of function's prototypes.  It includes _their_code_.

I mean the runtime library headers, not the import libs.
> Next, what do you mean by ``local defines'', and what is that "fatal 
> error 2373"?  E.g., can you compile, link, and run the following toy 
> program (which is a simplified replacement for the CHDIR command)?
> If this compiles at the highest possible warning level and runs and 
> expected, why can't we throw together a unistd.h and use it?  What am 
> I missing?
> -------------------------------------------
>  _CRTIMP int __cdecl _chdir(const char *);
>  int main(int argc, char *argv[])
>  {
>     if (argc > 1)
>        _chdir(argv[1]);
>     return 0;
>  }
> -------------------------------------------
Visual Studio, link to msvcrt.lib, compile with /W4 This is actually tricky
Made some test with different variants of this

1) No, _CRTIMP undefinied
2) Add #include <stdlib.h> at the top
   No, error LNK2019: unresolved external symbol "int __cdecl _chdir(char
const *)"
3) Change prototype to "int _chdir(const char *);
   No, error LNK2019: unresolved external symbol _chdir
4) Change prototype to "int __cdecl _chdir(const char *);
   No, error LNK2019: unresolved external symbol _chdir
5) Exchange prototype with #include <direct.h>
   Yes, no problem - works also with /Gz (__stdcall)

<direct.h> extracts

#ifdef  _MSC_VER
#pragma pack(push,8)   // 8 byte alignment - compiler default
#endif  /* _MSC_VER */

_CRTIMP int __cdecl _chdir(const char *);

No 2 should logically work, but don't. Strange enough I got no 3 to work
once, but couldn't reproduce it later. Conclusion: The only safe way is to
include the right headers and disable any local attempt to define the CRT
functions again.

> I need to see how it defines chdir, dup2, environ, getpid, and mktemp, 
> without the leading underscores.
> Also, what is the precise definition of _CRTIMP?
> > there is also prototypes for oldnames.lib functions (no underscore 
> > function aliases)

The meaning of _CRTIMP is to direct the compiler to either
__declspec(dllimport) or __declspec(dllexport) or nothing.

<direct.h> states:
#ifndef _CRTIMP
#ifdef  _DLL
#define _CRTIMP __declspec(dllimport)
#else   /* ndef _DLL */
#define _CRTIMP
#endif  /* _DLL */
#endif  /* _CRTIMP */

We are a program so _DLL is not defined => _CRTIMP means nothing.
However, apparently this is not as simple as it looks.

> > So, if you plan what I think you're planning - don't, it's
> not a good idea.> ??? Please explain why.  Especially since MinGW, 
> evidently, uses similar techniques to create its version of unistd.h, 
> as Earnie told us just now.

As you see, I have no good answer of this. I just think it will very
difficult to get locally defined prototypes of the CRT functions to be
accepted by the compiler. And what about the calling convention issues?

I think you all make this more difficult then it really is:
A simple fact:
* The Microsoft/Intel compiler don't like these prototypes. 
Solution: Disable them if using MSC. Include <direct.h>

Regards JB

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