[macstl-dev] template with C linkage

[Glen Low]

David:

On 06/02/2005, at 2:28 AM, David Chilton wrote:

> Glen,
> After much tinkering, it seems the problem comes in with the  
> -Wp,-header-mapfile,... option that is passed by Xcode.  I couldn't  
> get benchmark.cpp to compile from the command line so i started  
> putting in options from the Xcode build results window until it built.  
>  Finally, and tried to compile the main.cpp given below.  It works  
> with the std valarray straight away, but gives errors when i try to  
> use macstl/valarry.  But It works when I add  
> -Wp,-header-mapfile,[PATH_TO_BENCHMARK_BUILD]/benchmark.hmap to the  
> gcc call, without that it gives loads of errors.  I can't seem to find  
> any documentation on the hmap file or how to make one work, or why it  
> deosn't work without it.
>
> Here's the command line that does build properly:
> /usr/bin/gcc-3.3 /Users/chiltie/Desktop/main.cpp -o  
> /Users/chiltie/Desktop/main -lstdc++ -DUSE_MACSTL  
> -Wp,-header-mapfile,/Users/chiltie/Desktop/macstl/mac/build/ 
> macstl.build/benchmark.build/benchmark.hmap
>
> here's the one that doesn't:
> /usr/bin/gcc-3.3 /Users/chiltie/Desktop/main.cpp -o  
> /Users/chiltie/Desktop/main -lstdc++ -DUSE_MACSTL

It's rather perplexing. I use almost the same command line as yours:

/usr/bin/gcc-3.3 main.cpp -lstdc++ -DUSE_MACSTL -I../macstl -o main.o

where the -I is the path to the base of the outermost macstl directory,  
and I get no errors.

Googling for "template with C linkage" turns up about 700+ pages, some  
detailing issues even with system headers on certain combinations of  
operating systems and machines.

So my trusty C++ detective says :-), it's because a (possibly system)  
header has an unterminated

extern "C" {

which then infects all subsequent headers that were #included after.

Now if
>
> And Here's a few lines of the error output (it gives over a thousand  
> total errors):
> In file included from /usr/include/macstl/valarray.h:86,
>                  from /Users/chiltie/Desktop/main.cpp:3:
> /usr/include/macstl/impl/valarray_vec.h:45: error: template with C  
> linkage
> /usr/include/macstl/impl/valarray_vec.h:150: error: template with C  
> linkage
> /usr/include/macstl/impl/valarray_vec.h:254: error: template with C  
> linkage
>

is the first lot of errors you get back from the compile, then all the  
#includes before line 86 were OK and the culprit should be #included  
from somewhere in vec.h header.

I suspect that one of your system headers inadvertently had its last  
line or so chopped off, thus causing an unterminated extern "C"  
directive, or perhaps it was some interaction with a macro definition.  
The #include <valarray> might not have gone through the exact same  
route and thus not triggered it. To narrow it down, try putting a  
simple template definition at various points in the my source along the  
#include path to see if you can trigger the error sooner:

e.g.

template <typename T> struct make_my_day
	{
	};

Some configuration questions that might be useful:
1.	What's the exact version of gcc? (Try gcc --version)
2.	Have you made any changes at all to the /usr/include/gcc headers?
3.	Did you install macstl at /usr/include/ or somewhere else? If the  
former, try putting it somewhere else and using an -I option like I did  
to see if the error goes away.

Anyone else try out David's code and got errors?



Cheers, Glen Low


---
pixelglow software | simply brilliant stuff
www.pixelglow.com