[RESOLVED] Difference between C and C++ mode / call function from VB

I want to develop a function in C/C++ to take a large string and search for keywords - and calling this function from VB.Net.

First - I was curious what the difference is between compiling in C and C++ modes?

Second - having never written a function in C/C++ - how would I code up the parameters for passing an array of "keywords" and a large "string" of text from VB.Net (using VS 2010).

Thanks!

Compiling in "C mode" (With the /TC switch) will treat all source code as C code, which will give you syntax errors if you write any C++ code in your source files. Given that C and C++ are so similar, I'm not sure exactly of the differences in how the compiler compiles when using the /TC (C) vs the /TP (C++) flag. A c++ compiler should be able to compile C code. Perhaps different assumptions can be made when optimizing C versus C++ code? Not sure.

I just tried this and it worked alright.
C code:

Code:

---

__declspec(dllexport) int firstIndexOfKeyword(char *str, char **keywords, int nKeywords) {
        int i, j, k;
        int keywordlen;
        int len = strlen(str);

        for(k = 0; k < nKeywords; k++)
        {
                keywordlen = strlen(keywords[k]);

                for(i = 0; i <= len - keywordlen; i++)
                {
                        for(j = 0; j < keywordlen; j++)
                        {
                                if(keywords[k][j] != str[i + j])
                                        j = keywordlen+1;
                        }

                        if(j == keywordlen)
                                return i;
                }
        }

        return -1;
}

---

And invoked from VB like this:

Code:

---

    <System.Runtime.InteropServices.DllImport("C:\Users\emil\Documents\visual studio 2010\Projects\CDll\Debug\CDll.dll", CallingConvention:=Runtime.InteropServices.CallingConvention.Cdecl)> _
    Public Function firstIndexOfKeyword(ByVal s As String, ByVal substr As String(), ByVal substrLength As Integer) As Integer
    End Function

    Sub Main()
        Dim text As String = "i had fancy italian food for lunch"
        Dim keywords As String() = {"meh", "feh", "italian"}
        Dim index As Integer = firstIndexOfKeyword(text, keywords, keywords.Length)
        Console.WriteLine("Index: {0}", index)
    End Sub

---

Thank you - this is great!

Question - I'm working on a solution in VS 2010 - all VB now - with 5 projects.

I want to add a new project for this C/C++ stuff - do I make it a MFC DLL - a CLASS LIBRARY??

I have never used MFC so I'm not even sure..what it is!
The class library project template uses C++/CLI, which may or may not be what you want!
Another option is to create a Win32 Project, then choose DLL under Application Type in the wizard. This will give you a totally blank C/C++ project that compiles to a DLL.

I did that - seemed to work - made a lot of stuff...

Check out this image - where do I put that function? Which of these files?

Does it go in StringLibrary.cpp?

Code:

---

// StringLibrary.cpp : Defines the exported functions for the DLL application.
//

#include "stdafx.h"

---

Hey - I did put that code in the StringLibrary.cpp file - did a BUILD on the solution - and all seemed to be ok.

Where do I put this code

Code:

---

<System.Runtime.InteropServices.DllImport("C:\Users\emil\Documents\visual studio 2010\Projects\CDll\Debug\CDll.dll", CallingConvention:=Runtime.InteropServices.CallingConvention.Cdecl)> _
    Public Function firstIndexOfKeyword(ByVal s As String, ByVal substr As String(), ByVal substrLength As Integer) As Integer
    End Function

    Sub Main()
        Dim text As String = "i had fancy italian food for lunch"
        Dim keywords As String() = {"meh", "feh", "italian"}
        Dim index As Integer = firstIndexOfKeyword(text, keywords, keywords.Length)
        Console.WriteLine("Index: {0}", index)
    End Sub

---

I tried pasting that into the project that wants to call this new C/C++ function - and got this error

'System.Runtime.InteropServices.DllImportAttribute' cannot be applied to instance method.

...and it would not allow me to add a REFERENCE to the STRINGLIBRARY project from the project that wants to call this C/C++ function.

Also - I cannot find a .DLL in that DEBUG folder - I thought the BUILD for sure would have made that for me...

I found the .dll and also fixed the error by adding SHARED

Public Shared Function firstIndexOfKeyword(ByVal s As String, ByVal substr As String(), ByVal substrLength As Integer) As Integer

Is that the right thing to do? This C/C++ function is being called by several threads running in the other application.

Ran the code - got to that point - and in the immediate window I did

Code:

---

?firstIndexOfKeyword("i had fancy italian food for lunch", {"meh", "feh", "italian"}, 3)
{"An exception 'Microsoft.VisualStudio.Debugger.Runtime.CrossThreadMessagingException' occurred"}
    _HResult: -2146232832
    _message: "Error in the application."
    Data: {System.Collections.ListDictionaryInternal}
    HelpLink: Nothing
    HResult: -2146232832
    InnerException: Nothing
    IsTransient: False
    Message: "An exception 'Microsoft.VisualStudio.Debugger.Runtime.CrossThreadMessagingException' occurred"
    Source: "Microsoft.VisualStudio.Debugger.Runtime"
    StackTrace: "  at Microsoft.VisualStudio.Debugger.Runtime.Main.ThrowCrossThreadMessageException(String formatString)    at System.Windows.Forms.SafeNativeMethods.GetWindowTextLength(HandleRef hWnd)    at System.Windows.Forms.Control.get_WindowText()    at System.Windows.Forms.Form.get_WindowText()    at System.Windows.Forms.Control.get_Text()    at System.Windows.Forms.Form.get_Text()    at System.Windows.Forms.Form.ToString()"
    TargetSite: {Void ThrowCrossThreadMessageException(System.String)}

---

And got a pop-up error about not finding the ENTRY point and this ugly cross threading error...

I'll have to look into why you are getting a cross threading error, but as to the entry point issue, Im afraid I failed to include that in my first post but you need to specify external C linkage by doing:

Code:

---

extern "C"
{
  // Your method goes in here.
}

---

I started a new thread here in the VB .Net section of the forum...

http://www.vbforums.com/showthread.php?t=676154

I'll try that EXTERN C thing - that has something to do with MANAGLED NAMES - right?

Quote:

---

Originally Posted by szlamany

I started a new thread here in the VB .Net section of the forum...

I'll try that EXTERN C thing - that has something to do with MANAGLED NAMES - right?

---

Yeah I'm not too read up on this but it defines how the compiler treats the code with regards to external linkage, and specifying C style linkage will not mangle the names.

Yeah - I got that far in my searching but the syntax is so new to me - and the solution files themselves - that I had no idea where to put anything...

Tried to find a good book - all I left the book store with is a pocket guide - at least I can start to understand syntax and operators and such...

I did see a comment that someone made that you should use C# if you want to work with lots of C/C++ functions. Is there truth to that?

Is C# the C-style version of VB.Net?

I'm going to be doing lots of multi-threading in all this as well...

Is C# the C-style version of VB.NET? I would say yes.

But for the statement that you should use C# if you want to work with lots of C/C++ functions. I'm not too sure about that. I'm not sure if you gain anything to your C/C++ "skills" by using C#, other than the fact that you will have to get used to the semicolons! (That alone can be THE reason for some!)

Other than that I think that there are so many other differences to get used to when doing C/C++ that the basic syntax is not one of the major ones (And thats about the only C/C++ knowledge you will gain from also doing C#).

I hope that made any sense. I got confused while writing so I bet its also confusing to read ;)

Over the past year and a half I've become really fluent in javascript - so that type of object and function naming experience is strong. Is that already got me halfway to using C?

Maybe it's time to abandon VB for C-style languages?

Can I really do something like that after 30+ years?

This is working now.

btw - do I have to REBUILD it if I change the function? Seems that putting the EXTERN "C" in and RUNNING my whole solution (which starts 4 projects running at the same time) didn't work - I had to REBUILD. Do I REBUILD everytime I alter the function in some way??

also - how do I break in the C++ function?

It says no symbols have been loaded for this document.

My path to the dll is in the debug folder

Code:

---

    <System.Runtime.InteropServices.DllImport("D:\ACS Desktop\dcx\dcx\Debug\StringLibrary.dll", EntryPoint:="firstIndexOfKeyword", CallingConvention:=Runtime.InteropServices.CallingConvention.Cdecl)> _
    Public Shared Function firstIndexOfKeyword(ByVal s As String, ByVal substr As String(), ByVal substrLength As Integer) As Integer
    End Function

---

If you make any changes to a source file, that file will have to be recompiled. I believe msvc abandoned the use of Makefiles in c/c++ projects since a couple of versions back, in favor for msbuild project files, but they work essentially the same I believe. If a source file has changed since last time the project was compiled, it needs to be compiled, or else you will not be using the most recent build. By Building the project, it will only compile the source files that contains changes, and re-link the final executable. This way the entire c/c++ project does not need to be recompiled each time you make changes. If you Rebuild the project on the other hand, it will
re-compile each of the source files regardless if they contain changes or not.

As to the second question, I have never really tried to debug native code in a DLL that is invoked from .NET application, this looks like the way to do it.

Ok - I got the unmanaged code in the C++ function to work with the VS debugger.

I had to go the the actual PROJECT I was calling the function from (not the overall SOLUTION - as I have several projects in this solution) - and under PROJECT PROPERTIES - DEBUG tab - check off ENABLE UNMANAGED CODE DEBUGGING.

And I gotta say this really slowed down the startup of that particular project when I run the whole solution (4 projects fire up at once when I do a run). I can visually see the delay in that project starting.

I will have to remember to toggle that option on and off based on whether I am coding in the C++ function...

Thanks for all your help - I'm marking this thread resolved.

Now I can do wicked fast string searching - at least I'm about to embark on that path!

btw - what do the "*" characters mean?

Code:

---

firstIndexOfKeyword(char *str, char **keywords, int nKeywords, int **markers)

---

I figured that they mean "array" and wanted to pass in an integer array of MARKERS by reference...

* deals with pointers. They have two uses: declaring pointer variables and dereferencing pointers.
In this case, it declares str as a pointer-to-char, and keywords as a pointer-to-pointer-to-char.
In the case of str, it will point to the beginning of the sequence of characters that makes up the string. And keywords will point to memory locations that in turn pointers to chars.

And as for the other use of the asterisk, say that you want to find 'what' character str is "pointing" at. You'd do:

Code:

---

char firstChar = *str;

---

You can then advance the pointer with ordinary arithmetics, and dereference it again to find the second character in the sequence:

Code:

---

char secondChar = *(++str);

---