[Bug c++/24164] New: Explicit instantiation of template has no effect.

["gcc-bugzilla at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

Here are three files that illustrate the problem.  
Header file "t.hpp":
	namespace arrpp {

	    template <typename B>
	    class A {
	    public:
		    A();
            };
	}

File implementing class A, called t.cc:

	#include "t.hpp"
	template class arrpp::A<char>;            // instatiate class
	template <typename B> arrpp::A<B>:: A(){} // define ctor

File containing main, called xt.cc:
	#include "t.hpp"
	int main(int argc, char **argv) { arrpp::A<char> x; }
	
Produce t.o and xt.o:
	gcc -c t.cc xt.cc

Examine symbols in t.o:
	nm t.o
(Produces no output, indicating that no symbols are defined.)

Try to link object files:
	 gcc -o xt xt.o t.o -lstdc++
	 xt.o: In function `main':
	 xt.cc:(.text+0x24): undefined reference to `arrpp::A<char>::A()'
	 collect2: ld returned 1 exit status

On a machine with g++-3.3, this code works fine (links and runs, producing no
output).

Environment:
System: Linux dogwood 2.6.8-1-k7 #1 Thu Oct 7 02:47:47 EDT 2004 i686 GNU/Linux
Architecture: i686

	
host: i486-pc-linux-gnu
build: i486-pc-linux-gnu
target: i486-pc-linux-gnu
configured with: ../src/configure -v --enable-languages=c,c++,java,f95,objc,ada,treelang --prefix=/usr --enable-shared --with-system-zlib --libexecdir=/usr/lib --enable-nls --without-included-gettext --enable-threads=posix --program-suffix=-4.0 --enable-__cxa_atexit --enable-libstdcxx-allocator=mt --enable-clocale=gnu --enable-libstdcxx-debug --enable-java-gc=boehm --enable-java-awt=gtk --with-java-home=/usr/lib/jvm/java-1.4.2-gcj-4.0-1.4.2.0/jre --enable-mpfr --disable-werror --enable-checking=release i486-linux-gnu

How-To-Repeat:
	See above.  Here is the preprocessor output for t.cc:

# 1 "t.cc"
# 1 "<built-in>"
# 1 "<command line>"
# 1 "t.cc"
# 1 "t.hpp" 1
namespace arrpp {

    template <typename B>
    class A {
    public:
 A();
    };
}
# 2 "t.cc" 2

template class arrpp::A<char>;

template <typename B>
arrpp::A<B>::
A(){}

	Here is the preprocessor output for xt.cc:

# 1 "xt.cc"
# 1 "<built-in>"
# 1 "<command line>"
# 1 "xt.cc"
# 1 "t.hpp" 1
namespace arrpp {

    template <typename B>
    class A {
    public:
 A();
    };
}
# 2 "xt.cc" 2

int main(int argc, char **argv) {
    arrpp::A<char> x;
}
------- Additional Comments From rogers at anthro dot utah dot edu  2005-10-01 17:04 -------
Fix:
Here is a patch for t.cc that provides a work-around.  It instantiates
the class by declaring a variable:

	--- t.cc	2005-10-01 10:53:33.038810604 -0600
	+++ t2.cc	2005-10-01 10:53:47.335552612 -0600
	@@ -1,6 +1,6 @@
	 #include "t.hpp"
 
	-template class arrpp::A<char>;
	+arrpp::A<char> foo;
 
	 template <typename B>
	 arrpp::A<B>::

-- 
           Summary: Explicit instantiation of template has no effect.
           Product: gcc
           Version: 4.0.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rogers at anthro dot utah dot edu
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i486-pc-linux-gnu
  GCC host triplet: i486-pc-linux-gnu
GCC target triplet: i486-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24164