Calling a C function from a VS C++ Form Application

[PapaGeek]

I need to be able to call some very old C functions from a form application. What I found on line was to use 'extern "C"' to let Visual Studio know how to handle the calling parameters. But I'm getting a compiler error and not sure where it is coming from.

I changed the Form1.h file as:

extern "C" char *doit();
	private: System::Void button1_Click(System::Object^  sender, System::EventArgs^  e) {
//				 richTextBox1->Text="Button Hit\nLine 2\nLine 3\nLine 4\nLine 5\nLine 6\nLine 7";
				 richTextBox1 = doit();
			 }
	private: System::Void richTextBox1_TextChanged(System::Object^  sender, System::EventArgs^  e) {
			 }

and the actual doit.c file as:

#include <stdio.h>

char *xyz = 0;

extern "C" char *doit()
{
	xyz = calloc(1, 1024);
	sprintf(xyz,"Button Hit\nLine 2\nLine 3\nLine 4\nLine 5\nLine 6\nLine 7");
	return xyz;
}

The error I'm getting is:

Command line error D8045: cannot compile C file '.\doit.c' with the /clr option File cl

Can this even be done?

If so, can someone point me to an example.

Thanks

[thines01]

Do you have the original source code?
If so, change the extension to .cpp, add the source to your project, make sure you're using warning level 4 and re-compile.

After you fix all of the (now-known-as) bugs, you'll be finished.

[PapaGeek]

Do you have the original source code?
If so, change the extension to .cpp, add the source to your project, make sure you're using warning level 4 and re-compile.

After you fix all of the (now-known-as) bugs, you'll be finished.

Thanks, that did work. The hardest piece of the puzzle was finding the "gcnew" keyword.

doit.CPP

#include "stdafx.h"

#include "stdio.h"
#include "stdlib.h"

char *xyz = 0;

extern "C" char *doit()
{
	xyz = (char *)calloc(1, 1024);
	sprintf(xyz,"Button Hit\nLine 2\nLine 3\nLine 4\nLine 5\nLine 6\nLine 7");
	return xyz;
}

and the change to form1.h

extern "C" char *doit();

moved outside namespace:

And the button1_Click code is now:

private: System::Void button1_Click(System::Object^  sender, System::EventArgs^  e) {
//				 richTextBox1->Text="Button Hit\nLine 2\nLine 3\nLine 4\nLine 5\nLine 6\nLine 7";
				 char *p = doit();

				 richTextBox1->Text = gcnew String(p);
			 }

It compiles and runs now

Thanks

Update: Simplify the code:

You can combine the lines

private: System::Void button1_Click(System::Object^  sender, System::EventArgs^  e) {
//				 richTextBox1->Text="Button Hit\nLine 2\nLine 3\nLine 4\nLine 5\nLine 6\nLine 7";
				 richTextBox1->Text = gcnew String(doit());
			 }