[Mingw-users] GCH precompiled headers and C++

[Martin F. <mar...@gm...>]

Hi,

I've got some problems using the new GCC 3.4 feature of precompiled =
headers with C++ programs.

This is what the manual page says:

> To create a precompiled header file, simply compile it as you would =
any other
> file, if necessary using the -x option to make the driver treat it as =
a C or C++
> header file.

So far so good. Now here is my little test case:


-- file gchtest.h ---

#include <iostream>


-- file gchtest.cpp ---

#include "gchtest.h"

using namespace std;

int main()
{
    cout << "Hello GCH !\n";

   return 0;
}


The Makefile for this simple test case would be something like this:

gchtest.exe: gchtest.h.gch gchtest.cpp
    g++ gchtest.cpp -o $@

gchtest.h.gch: gchtest.h
    g++ gchtest.h

But I didn't find a way to get it working.


Trying to generate the GCH file using g++ results in this error
(This works flawless in a native Linux build environment.):

...\gchtest>g++ gchtest.h
gchtest.h:2: fatal error: can't read =
E:\DOCUME~1\Martin\LOCALS~1\Temp/ccYPaaaa.s
: No such file or directory
compilation terminated.


Trying to generate the GCH file using gcc results in this error:

...\gchtest>gcc gchtest.h
gchtest.h:1:20: iostream: No such file or directory

This one is OK, since "iostream" is a C++ header file.


Trying to generate the GCH file using gcc with option "x c++" results in =
linker errors:

...\gchtest>gcc gchtest.h
gchtest.h:1:20: iostream: No such file or directory

D:\src\examples\gchtest>gcc -x c++ gchtest.h
E:\DOCUME~1\Martin\LOCALS~1\Temp/cc08baaa.o(.text+0xd):gchtest.h: =
undefined reference to `std::string::size() const'
E:\DOCUME~1\Martin\LOCALS~1\Temp/cc08baaa.o(.text+0x60):gchtest.h: =
undefined reference to `std::string::operator[](unsigned) const'
E:\DOCUME~1\Martin\LOCALS~1\Temp/cc08baaa.o(.text+0x9f):gchtest.h: =
undefined reference to `std::string::operator[](unsigned) const'
E:\DOCUME~1\Martin\LOCALS~1\Temp/cc08baaa.o(.text+0xce):gchtest.h: =
undefined reference to `std::string::operator[](unsigned) const'
E:\DOCUME~1\Martin\LOCALS~1\Temp/cc08baaa.o(.text+0x11d):gchtest.h: =
undefined reference to `std::ios_base::Init::Init()'
E:\DOCUME~1\Martin\LOCALS~1\Temp/cc08baaa.o(.text+0x138):gchtest.h: =
undefined reference to `std::ios_base::Init::~Init()'
E:/MinGW/bin/../lib/gcc/mingw32/3.4.0/../../../libmingw32.a(main.o)(.text=
+0x97):
main.c: undefined reference to `WinMain@16'
collect2: ld returned 1 exit status


It seems gcc treats the header file "gchtest.h" as a C++ file, compiles =
it, and automatically invokes the linker instead of generating the =
precompiled header file!


I tried one more variation of command line arguments:

...\gchtest>gcc -x c++ -c gchtest.h

This one doesn't print an error message, but it generates an object file =
"gchtest.o" instead of the "gchtest.h.gch" file.


So there seems to be a bug in the MinGW g++ frontent regarding =
precompiled header support. Can anyone confirm this or even fix the =
problem?


Regards,

   Martin