P/Invoke Libraries for C++ Assemblies
in [CSharp]
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From: jp2msft on 10 Jun 2010 08:05 I've got a library from a government agency that only comes with the .lib and a header (.h) file. The header shows me what methods are exposed, but I'm not sure if I can get to those features through a .Net Framework. If I want to call one of the four (4) exported methods of the DLL, how would I go about formatting the P/Invoke call to them? Here is an example of one of the exposed methods (from the header): extern void standardCalc(double param(), double inputs(), double outputs()); I'm getting rather used to C# syntax, but I think "double param()" is an array of doubles - what I'd call "double[] param" in C#. If I am mistaken, please correct me! So, how would I go about invoking this exposed method from the library file "aesra10.lib"? Also, all examples of P/Invoke only list the file name, not it's location. Do all files that I invoke this way have to be in a certain folder or can I direct it to the folder where my application will be storing this DLL?
From: Jason Keats on 10 Jun 2010 10:02 jp2msft wrote: > I've got a library from a government agency that only comes with the .lib and > a header (.h) file. > > The header shows me what methods are exposed, but I'm not sure if I can get > to those features through a .Net Framework. > > If I want to call one of the four (4) exported methods of the DLL, how would > I go about formatting the P/Invoke call to them? > > Here is an example of one of the exposed methods (from the header): > > extern void standardCalc(double param(), double inputs(), double outputs()); > > I'm getting rather used to C# syntax, but I think "double param()" is an > array of doubles - what I'd call "double[] param" in C#. If I am mistaken, > please correct me! > > So, how would I go about invoking this exposed method from the library file > "aesra10.lib"? > > Also, all examples of P/Invoke only list the file name, not it's location. > Do all files that I invoke this way have to be in a certain folder or can I > direct it to the folder where my application will be storing this DLL? I'm pretty sure you can't directly access functions within the static library file aesra10.lib. You will first need to use C/C++ to link it into a dynamic (.dll) library of your making. You should then be able to use P/Invoke from C# to access its functions. Once you've made a dll you should put it in the same folder as your program.
From: Jeff Johnson on 10 Jun 2010 11:24 "jp2msft" <jp2msft(a)discussions.microsoft.com> wrote in message news:666994F8-19A3-4B6B-8E43-4AA4C8D8235E(a)microsoft.com... > Here is an example of one of the exposed methods (from the header): > > extern void standardCalc(double param(), double inputs(), double > outputs()); Did you copy and paste that directly from the header? I don't claim to be a C++ expert but I cannot see how that can possibly be valid syntax. Arrays would be expressed as extern void standardCalc(double[] param, double[] inputs, double[] outputs); I was just recently reading a book on C++ to knock the rust off my skills because I was thinking of writing a program under Linux and I never saw anything even remotely similar to the syntax you have above.
From: Peter Duniho on 10 Jun 2010 11:39 jp2msft wrote: > I've got a library from a government agency that only comes with the .lib and > a header (.h) file. As Jason says, you can't link to a static .lib from C#. > The header shows me what methods are exposed, but I'm not sure if I can get > to those features through a .Net Framework. > > If I want to call one of the four (4) exported methods of the DLL, how would > I go about formatting the P/Invoke call to them? > > Here is an example of one of the exposed methods (from the header): > > extern void standardCalc(double param(), double inputs(), double outputs()); That does not look like correct C to me. Parens are used only for function declarations and calls when paired with an identifier (they are also, of course, used for certain program statements and expression grouping). Parameters used to pass arrays would use square brackets like C#, but with the parameter name, not the type name. For example, "double param[]". > I'm getting rather used to C# syntax, but I think "double param()" is an > array of doubles - what I'd call "double[] param" in C#. If I am mistaken, > please correct me! > > So, how would I go about invoking this exposed method from the library file > "aesra10.lib"? The first step is to get it into a DLL, which means wrapping the static ..lib in a DLL. One way to do that is to create a new empty C/C++ DLL project, link the .lib into the project, and write a .def file that exports the members of the .lib. Alternatively, you can wrap each member of the .lib that you want to expose in a simple wrapper that is exported from the DLL project instead. This method is a little less efficient, but IMHO is preferable because it allows you to use the declspec(dllexport) modifier in your wrapper code rather than messing around with a .def file (I find declaring exports in-code more intuitive than using a .def file…YMMV). Either of those techniques should work fine as long as the original .lib is plain C. If it's C++, then you'll have to wrap the C++ in some kind of managed-code-accessible thing. The easiest way to do that is to just build a mixed-mode managed C++ DLL (i.e. a managed C++ DLL that's not "/clr:pure"). Then you can implement .NET types in the DLL that wrap the unmanaged types from the .lib. Having done that, the DLL will be usable just like any other .NET managed DLL. One nice thing about this approach is that it gives you the opportunity to wrap the original .lib in a more user-friendly managed API, rather than forcing anyone using the library from managed code to have to deal with the API from the .lib (which is almost certainly not going to use .NET idioms and conventions). You'll still have to do some marshaling yourself (see the Marshal class and related attributes such as MarshalAsAttribute in the System.Runtime.InteropServices namespace), but the C++ compiler knows how to deal with simple things like strings, and provides a "pin_ptr" type for locking down arrays and other managed objects so they can be passed directly to unmanaged code conveniently. > Also, all examples of P/Invoke only list the file name, not it's location. > Do all files that I invoke this way have to be in a certain folder or can I > direct it to the folder where my application will be storing this DLL? P/invoke will need the DLL to be present either in the same directory with the program, or in the DLL search path (mainly the System32 directory, if I recall correctly). I don't think you can change the DLL search path programmatically, but I might be mistaken about that. Pete
From: Doug Forster on 10 Jun 2010 16:56
> > That does not look like correct C to me. Parens are used only for > function declarations and calls when paired with an identifier (they are > also, of course, used for certain program statements and expression > grouping). It's perfectly correct C but it doesn't mean what the OP thinks. If that really is the declaration then it means a pointer to a function with no parameters that returns a double result. Cheers Doug Forster |