Re: Const structure pointer as template argument

• Subject: Re: Const structure pointer as template argument
• From: Ladd Van Tol <email@hidden>
• Date: Fri, 30 Jun 2006 10:57:36 -0700
• Delivered-to: email@hidden
• Delivered-to: email@hidden

On Jun 30, 2006, at 9:30 AM, David Fang wrote:

Hi,
	Instances that are passed as template arguments need to be
declared with external linkage.  In your case, you need to forward
declare:

//------------ >8 snip 8<-------------------
struct testStruct {
        long a;
};

template <const testStruct* bob> class Helper { };

extern const testStruct constTestStruct;	// EXTERN DECLARE!

const testStruct constTestStruct = {0};		// static initialization
Helper<&constTestStruct> HelperConst;		// binding argument

//------------ >8 snip 8<-------------------

Now this compiles on your first example.

Otherwise static linkage (of the instance argument) may result in multiple
definitions in different translation units with the same argument name,
referring to different types (because the symbols differ).

Aha. This makes sense, and your extern fix does indeed work.

Admittedly, the error messages in all 4.x versions of gcc could be
improved.  May I submit your testcase to gcc.gnu.org?

Agreed on the error message -- feel free to submit the testcase.

Thanks,

	Ladd

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