template question

[akcom]

Regan Heath wrote:
> On Wed, 31 May 2006 19:55:40 -0400, akcom <CppCoder at gmail.com> wrote:
>> I am translating a C macro I use while manipulating PE files, it has 
>> the following definition:
>>
>> #define incptr( Ptr, Increment, CastType ) (CastType *)( (unsigned 
>> long)(Ptr) + (unsigned long)(Increment) )
>>
>> I thought using templates would be best, so I came up with the following:
>>
>> template IncPtr( Ptr:Ptr *, int Increment, T )
>> {
>>     const IncPtr = cast(T *)( cast(uint)Ptr + Increment );
>> }
>>
>> unfortunately, when I try to use it with something like the following...
>> IMAGE_DOS_HEADER *dosHeader;
>> IMAGE_NT_HEADERS *ntHeaders;
>>
>> ntHeaders = IncPtr!( dosHeader, dosHeader.e_lfanew, IMAGE_NT_HEADERS );
>>
>> I get the following compilation errors:
>> pefile.d(194): template instance IncPtr!(dosHeader,incr,ImageNtHeaders 
>> ) does not match any template declaration
>> pefile.d(194): voids have no value
>> pefile.d(194): cannot implicitly convert expression 
>> (IncPtr!(dosHeader,incr,Imag
>> eNtHeaders )) of type void to ImageNtHeaders *
>>
>> any ideas?
> 
> I'd probably do it like this:
> 
> typedef int IMAGE_DOS_HEADER;
> typedef int IMAGE_NT_HEADERS;
> 
> template IncPtr(T){ T* IncPtr(T* Ptr, int Increment) {
>     return cast(T*)(cast(ubyte*)Ptr + Increment);
> }}
> 
> void main()
> {
>     IMAGE_NT_HEADERS* a;
>     IMAGE_DOS_HEADER* b;
>     
>     b = cast(IMAGE_DOS_HEADER*)IncPtr(a,5);
> }
> 
> Notes:
> 
> A template function is used. I'm hoping it gets inlined.
> 
> cast(byte*) is used instead of cast(uint); on 64 bit systems, do 
> pointers fit into a uint?
> 
> The resulting type is not included in the IncPtr template, I prefer to 
> do it explicitly. This allows implicit template argument deduction to 
> function and it just seems more natural/correct to me.
> 
> Regan
Thank you very much for your help