On Mon, Aug 23, 2004 at 10:30:54AM +0200, Markus Sch?pflin wrote:
Hello,
currently beforementioned test fails on tru64cxx65 with the following error message:
cxx: Error: ../libs/algorithm/string/test/container_test.cpp, line 94: #434 a reference of type "char *&" (not const-qualified) cannot be initialized with a value of type "char [4]" argument_test( ach1, "abc" );
Long answer: The difference between Comeau and cxx is that Comeau (and also GCC) instantiates the template with T = char[4], binding a reference to that type. cxx does an array-to-pointer conversion and then instantiates the template with that type, and so fails to bind a non-const ref to the char* temporary. You can see the type Comeau and GCC instantiate the template with by adding "no_such_function(C);" into the body of argument_test(), as the resulting diagnostics will include "[with T=char [4]]" or similar. The standard says that template argument deduction of type T happens for an expression of the type "T[integer-constant]" which covers the case of "char[4]", see example in para 10 of [temp.deduct.type] which deals with types composed of the simpler types. It also says that if a template function argument has been determined by template argument deduction, that argument cannot also have promotions, standard conversions, or user-defined conversions applied. That wording is from Stroustrup, the corresponding text in the standard is para 1 [temp.over] IIUC. AFAICT array-to-pointer conversion should only happen on a template parameter for a non-type parameter. Short answer: I think tru64cxx65 is wrong. jon
The underlying problem is illustrated by the following code snippet:
---%<--- template< typename T > void argument_cv_test( const T& C, const string& strResult ) { }
template< typename T > void argument_test( T& C, const string& strResult ) { }
void foo() { char ach1[]="abc"; argument_cv_test( ach1, "abc" ); // ok argument_test( ach1, "abc" ); // not ok } --->%---
The line marked as not ok triggers the error. I tried to compile that code snippet with Comeau online and it succeeds. But I could not find a definitive answer in the C++ standard whether that code is legal or not.
If it's legal, could anyone please provide me with a reference to the paragraph of the standard which applies here? I would need that to file a proper bug report to HP.
TIA, Markus
_______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
-- "The tools we use have a profound (and devious!) influence on our thinking habits, and, therefore, on our thinking abilities." - Edsger Dijkstra