Re: dllexport template function: char* parameter problem

From:

Ulrich Eckhardt <eckhardt@satorlaser.com>

Newsgroups:

microsoft.public.vc.language

Date:

Mon, 21 Apr 2008 13:43:09 +0200

Message-ID:

<d7bud5-sdf.ln1@satorlaser.homedns.org>

Fabian wrote:

last week I got the suggestion to write template functions for my error
handling. With the implementation I've got a little problem: As the
functions are in a separate dll, I have to instantiate them explicitely in
the cpp file. This works fine for parameters of type int or double. The
main purpose of my error printing function is to print a message though.

Why do you insist on having all instantiations in the DLL? Why not simply
put the non-template parts into the DLL and make the rest inline? In case
you are afraid that this will blow up the size of your executables, I'm
afraid you are optimising prematurely.

template <typename T1> void TEMPLDLL_API PrintError(const T1& arg1);

[...]

error LNK2019: unresolved external symbol "__declspec(dllimport) void
__cdecl PrintError<char const [20]>(char const (&)[20])" ...

If I now cast the string to a char* the error is
gone: ErrorHandling::PrintError((char*)"There was an error."); // works

This is really ugly though esp. for an overload with several parameters.
More than ever if I do it the clean c++ way with static_cast<char*>("There
was an error");.

Ahem, the clean C++ way would be to cast to a pointer to const char. ;)

Anyway, due to the rules of C++ template parameter deduction it picks a
reference to a const char array as parameters. However, you could also
write it this way:

PrintError<char const*>("No problem!");

i.e. explicitly set the parameters.

Uli

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