In-source way to call any C Library

[Adrian Iliescu]

Is there a way to call a C function without having to screw around with the
linker on the command line?  In C#, for example, this is all you have to do:

[DllImport( @..\Debug\CLibTest.dll )]//location
internal static extern int MyTestResult(); //name of function

void CSUsingCLib()
{
int result = MyTestResult(); //use it
}

Re: In-source way to call any C Library

[Jacob Carlborg]

On 2011-03-18 19:54, Adrian Iliescu wrote:

Is there a way to call a C function without having to screw around with the
linker on the command line?  In C#, for example, this is all you have to do:

 [DllImport( @..\Debug\CLibTest.dll )]//location
 internal static extern int MyTestResult(); //name of function

 void CSUsingCLib()
 {
 int result = MyTestResult(); //use it
 }


With pragma(lib, lib); you can link to a library: 
http://www.digitalmars.com/d/2.0/pragma.html


And then using extern(C) as usual to declare the function. You can also 
use dlopen and friends on Posix and whatever the equivalent is for 
Windows.


--
/Jacob Carlborg

Re: In-source way to call any C Library

[Andrej Mitrovic]

For runtime linking with DLLs, you're looking for LoadLibrary,
GetProcAddress and friends. They're in core.sys.windows.windows.

The static constructor is useful if you want to have C functions in
module scope. Personally, I wrap C libraries in classes and hide all
the loading details there.

However the following is what I think you're after:
module testDllLoad;

import std.stdio;
import std.string;
import std.path : join, curdir;
import core.sys.windows.windows;
import std.exception;

extern(C) int function() MyTestResult;

static this()
{
string dllFileName = join(r..\Debug\, CLibTest.dll);
HMODULE dllModule;
enforce(dllModule = LoadLibraryA(toStringz(dllFileName)));
enforce(MyTestResult = GetProcAddress(dllModule, _MyTestResult));
}

void CSUsingCLib()
{
int result = MyTestResult();  // use it
writeln(result);
}

void main()
{
CSUsingCLib();
}

I've tested this with a C DLL which exports the function
_MyTestResult. The DLL was located in the previous directory, under
Debug, just like your example. It worked fine.

Btw, in case you don't know, its very important to specify the calling
convention and the /correct/ calling convention for a function. For a
C DLL this is always extern(C).

Re: In-source way to call any C Library

[Jesse Phillips]

Adrian Iliescu Wrote:

 Is there a way to call a C function without having to screw around with the
 linker on the command line?  In C#, for example, this is all you have to do:
 
 [DllImport( @..\Debug\CLibTest.dll )]//location
 internal static extern int MyTestResult(); //name of function
 
 void CSUsingCLib()
 {
 int result = MyTestResult(); //use it
 }

You may find the Library referenced here useful:
 http://stackoverflow.com/questions/3818229/loading-plugins-dlls-on-the-fly