Re: c++/7166: Non-type template instantiation fails for pointer types

Re: c++/7166: Non-type template instantiation fails for pointer types

[nathan]

Synopsis: Non-type template instantiation fails for pointer types

State-Changed-From-To: open->closed
State-Changed-By: nathan
State-Changed-When: Sun Jun 30 02:57:04 2002
State-Changed-Why:
    not a bug. Like the error says, you are attempting to
    instantiate a template on a non-externally visible object
    (the thing pointer to *by* strPointer). The array case
    works becuase of array->pointer decay - the thing pointed
    to is the first array element, and that does have external
    linkage. May be you mean to write
    	template <char const *&r> class Foo {};
    which would be acceptable for the first case, as then you're
    binding to the pointer variable.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=7166

c++/7166: Non-type template instantiation fails for pointer types

[ofv]

>Number:         7166
>Category:       c++
>Synopsis:       Non-type template instantiation fails for pointer types
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          rejects-legal
>Submitter-Id:   net
>Arrival-Date:   Sat Jun 29 11:56:02 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator:     ofv@wandoo.es
>Release:        gcc 3.1
>Organization:
>Environment:
d:/Des/cppExp # gcc -v
Reading specs from t:/msys/1.0/mingw/bin/../lib/gcc-lib/mingw32/3.1/specs
Configured with: ../gcc/configure --with-gcc --with-gnu-ld --with-gnu-as --host=mingw32 --target=mingw32 --prefix=/mingw --enable-threads --disable-nls --enable-languages=f77,c++,objc,ada --disable-win32-registry --disable-shared
Thread model: win32
gcc version 3.1

It fails too with gcc 3.1 (cygwin) and gcc 2.95.3-6 (MinGW)
>Description:
Instantiating a template with a non-type parameter of pointer type makes the compiler complain about the parameter not being an object with external linkage. So far I've only tried with char* and int*. It works for char[] and int[].

See test case below.
>How-To-Repeat:
Compiling this:

/// begin

template <char *p> class FooChar {};

char *strPointer = "Hi!";
char  strArray[] = "Hi!";

template <int *p> class FooInt {};

int *intPointer = 0;
int  intArray[] = { 1, 2 };

int main() {
  FooChar<strPointer> fooCharPointer;
  FooChar<strArray> fooCharArray;

  FooInt<intPointer> fooIntPointer;
  FooInt<intArray> fooIntArray;
}

/// end

produces

g++ -c gccbugTPointer.cpp
gccbugTPointer.cpp: In function `int main()':
gccbugTPointer.cpp:12: `strPointer' is not a valid template argument
gccbugTPointer.cpp:12: it must be the address of an object with external linkage
gccbugTPointer.cpp:12: ISO C++ forbids declaration of `fooPointer' with no type
gccbugTPointer.cpp:15: `intPointer' is not a valid template argument
gccbugTPointer.cpp:15: it must be the address of an object with external linkage
gccbugTPointer.cpp:15: ISO C++ forbids declaration of `fooIntPointer' with no type
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted: