Marshal::StringToHGlobalAnsi and the corresponding overhead

  • Thread starter Thread starter DaTurk
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DaTurk

Hi,

I have a c# GUI that needs to untimately send its data down to
unmanaged c++. I've decided to do this by having a ref struct in the
CLI layer and have the c# populate this, and then pass it back to the
CLI layer. The CLI layer will then populate the unmanged struct where
the data needs to end up.

Now, my question, I just realized that I'm going to have alot of
strings. I need to have these things end up as char*, but they start
as String^. I'm just thinking about overhead, I was thinking about
Marshalling the strings via Marshal::StringToHGlobalAnsi, but I'm a
little worried about the overhead. Any ideas?

Thanks in advance.
 
DaTurk said:
Now, my question, I just realized that I'm going to have alot of
strings. I need to have these things end up as char*, but they start
as String^. I'm just thinking about overhead, I was thinking about
Marshalling the strings via Marshal::StringToHGlobalAnsi, but I'm a
little worried about the overhead. Any ideas?
Click to expand...

If you don't plan to modify the strings you can use PtrToStringChars():

http://blogs.msdn.com/slippman/archive/2004/06/02/147090.aspx

IMO, it's only by profiling that you'll be able to determine if your worries
are warranted or if one method is materially better than another.

Regards,
Will
 
DaTurk said:
Hi,

I have a c# GUI that needs to untimately send its data down to
unmanaged c++. I've decided to do this by having a ref struct in the
CLI layer and have the c# populate this, and then pass it back to the
CLI layer. The CLI layer will then populate the unmanged struct where
the data needs to end up.

Now, my question, I just realized that I'm going to have alot of
strings. I need to have these things end up as char*, but they start
as String^. I'm just thinking about overhead, I was thinking about
Marshalling the strings via Marshal::StringToHGlobalAnsi, but I'm a
little worried about the overhead. Any ideas?
Click to expand...

Most of the overhead there is in Unicode->ANSI conversion. If the client
 
Hi,
Click to expand...
I have a c# GUI that needs to untimately send its data down to
unmanaged c++. I've decided to do this by having a ref struct in the
CLI layer and have the c# populate this, and then pass it back to the
CLI layer. The CLI layer will then populate the unmanged struct where
the data needs to end up.
Click to expand...
Now, my question, I just realized that I'm going to have alot of
strings. I need to have these things end up as char*, but they start
as String^. I'm just thinking about overhead, I was thinking about
Marshalling the strings via Marshal::StringToHGlobalAnsi, but I'm a
little worried about the overhead. Any ideas?
Click to expand...

Most of the overhead there is in Unicode->ANSI conversion. If the client
can use byte[] (cli::array<System::Byte>^) instead, it will be faster.
Depends on whether it acts like character strings or raw byte data.




Thanks in advance.- Hide quoted text -
Click to expand...

- Show quoted text -
Click to expand...

That's interesting, I didn't think about that. There will still have
to be someconversion at some point as the information I'm going to be
using is going to be coming from a WinForm, so it will be of the type
String^ at the presentation layer. SO I huess the question then
becomes, would it be more costly to convert a String^ -> a byte[] at
the presentation layer, or to convert a String^ -> a char* down lower
in the program?
 
That's interesting, I didn't think about that. There will still have
to be someconversion at some point as the information I'm going to be
using is going to be coming from a WinForm, so it will be of the type
String^ at the presentation layer. SO I huess the question then
becomes, would it be more costly to convert a String^ -> a byte[] at
the presentation layer, or to convert a String^ -> a char* down lower
in the program?
Click to expand...

I think the Unicode->ANSI conversion may be implemented differently in .NET
vs native, so that could be a consideration too. Otherwise, I don't see why
either path would be any faster. I would probably hand a String^ to C++ to
keep the presentation layer free from implementation details.

My basic suggestion was that not all char* start life as strings, some are
more "magic numbers". E.g. in SMTP, the "MAIL TO:" command isn't a string
subject to localization, it has to be those exact bytes. Similarly for HTML
tags and the filetype codes used by a lot of programs (GIF does this).
Yours is user-entered though, so you do need the conversion.
 
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