Re: Template trouble
Re: Template trouble
- Subject: Re: Template trouble
- From: Steve Checkoway <email@hidden>
- Date: Mon, 28 Aug 2006 17:11:53 -0700
On Aug 28, 2006, at 1:00 PM, Edward K. Chew wrote:
Oh, I forgot to mention, I have run into trouble with template
specialization. For example, I have a function along the lines:
template <typename T> UInt32 myHashFunction(T value, int
hashBitLength);
I specialized this for C strings:
template <> UInt32 myHashFunction(const char *str, int hashBitLength);
In most cases, I use a string and get the specialized version, but
in a few situations, I get the general implementation instead. I
experimented with partial specialization (i.e. ...myHashFunction
(const T *pointer... ), but it still goes with the general case.
The debugger says that the class from which I call myHashFunction
is of type myClass<char const *>, but I believe "const char *" and
"char const *" are equivalent in C++. Anyway, I tried every
permutation I could think of to no avail.
I have a guess why this might be happening.
[PBG4:~/temp] steve$ cat template.cc
#include <cstdio>
template <typename T> void f( T t ) { puts( "general" ); }
template<> void f<const char *>( const char *s ) { puts( s ); }
int main()
{
char foo[] = "non const";
const char *bar = "const";
f( foo );
f( bar );
return 0;
}
[PBG4:~/temp] steve$ g++ -Wall -std=c++98 template.cc
[PBG4:~/temp] steve$ ./a.out
general
const
As you can see, the general version will be called for char*.
Personally, I can never remember the matching rules so I always have
to test this stuff out.
--
Steve Checkoway
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