mathlink or wstp - Write C/C++ programs calling Mathematica functions

I need to write a C/C++ program and call some functions in Mathematica especially those like Solve or NDSolve. The problem is that in the Mathematica documentation it seems to me there is no mention about this.

There are plenty of details regarding how to create a C function and then call it from within Mathematica, but in my case I need the opposite.

Maybe I did not read well, but can you explain me how to do this?

Answer

Have a look at this;

http://reference.wolfram.com/mathematica/guide/MathLinkCLanguageFunctions.html

I haven't used it in C/C++ but it works fine in C# and Java. Basically you create a connection to a Mathematica kernel and then pass it native data types. Works nicely.

Here is some sample code in Java that I used when I first did this;

import com.wolfram.jlink.*;

public class SampleProgram {


public static void main(String[] argv) {

    KernelLink ml = null;

    try {
        ml = MathLinkFactory.createKernelLink(argv);
    } catch (MathLinkException e) {
        System.out.println("Fatal error opening link: " + e.getMessage());
        return;
    }


    try {
        // Get rid of the initial InputNamePacket the kernel will send
        // when it is launched.
        ml.discardAnswer();

        ml.evaluate("<        ml.discardAnswer();

        ml.evaluate("2+2");

        ml.waitForAnswer();

        int result = ml.getInteger();
        System.out.println("2 + 2 = " + result);

        // Here's how to send the same input, but not as a string:
        ml.putFunction("EvaluatePacket", 1);
        ml.putFunction("Plus", 2);
        ml.put(3);
        ml.put(3);

        ml.endPacket();
        ml.waitForAnswer();
        result = ml.getInteger();
        System.out.println("3 + 3 = " + result);

        // If you want the result back as a string, use evaluateToInputForm
        // or evaluateToOutputForm. The second arg for either is the
        // requested page width for formatting the string. Pass 0 for
        // PageWidth->Infinity. These methods get the result in one
        // step--no need to call waitForAnswer.

        String strResult = ml.evaluateToOutputForm("4+4", 0);
        System.out.println("4 + 4 = " + strResult);

    } catch (MathLinkException e) {
        System.out.println("MathLinkException occurred: " + e.getMessage());
    } finally {
        ml.close();
    }
}
}

The connection string argv should look something like this

String argv = "-linkmode launch -linkname 'C:\\Program Files\\Wolfram Research\\Mathematica\\8.0\\mathkernel.exe'";

http://reference.wolfram.com/mathematica/JLink/tutorial/WritingJavaProgramsThatUseMathematica.html