Write C/C++ programs calling Mathematica functions

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("<<MyPackage.m");
        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

The other answers ignore that you are asking about C or C++ (not C# or Java!)

Mathematica can be called from C (or C++) through the MathLink interface (recently renamed to WSTP). To learn it, I recommend reading this old MathLink tutorial by Todd Gayley:

• Original version in PostScript: http://library.wolfram.com/infocenter/Demos/174/
• PDF conversion: http://edenwaith.com/development/tutorials/mathlink/ML_Tut.pdf

Section 2 discusses what you are asking for: calling Mathematica from a C program rather than the reverse case (which is better covered in the official documentation)

You will find several example programs (like factor.c) in the directory opened by this command:

SystemOpen@
 FileNameJoin[{$InstallationDirectory, "SystemFiles", "Links", 
   "MathLink", "DeveloperKit", $SystemID, "MathLinkExamples"}]

It is also useful to experiment with setting up MathLink connections in pure Mathematica code. This will help you understand the basic procedure before you try to implement the same in C:

• http://reference.wolfram.com/language/tutorial/CallingSubsidiaryWolframSystemProcesses.html

C Style

To Call Mathematica functions from C/C++ you need to use ML_ or WS_ functions. Mathematica is now "replacing" MathLink with WSTP. However function names are mostly similar. There are C style WSPutT functions that are used to send an input of type T to mathematica. and the output is fetched from mathematica using WSNextPacket and WSGetT functions. To use these accessing functions first a link needs to be established WSOpenArgcArgv. The C language Reference lists the functions that you will need to communicate with mathematica using C/C++

C++ (with mathematica++)

I was mostly interested to use mathematica from C++. So I developed one C++ library mathematica++ that uses template magic for easier interoperability between C++ and Mathematica. The usage example below is copied from the project page.

symbol x("x");
value  res;
std::string method = "Newton";

shell << Values(FindRoot(ArcTan(1000 * Cos(x)), List(x, 1, 2),  Rule("Method") = method));
shell >> res;
std::vector<double> results = cast<std::vector<double>>(res);
std::cout << results[0] << std::endl; // Prints 10.9956

With mathematica++ you declare a mathematica function using MATHEMATICA_DECLARE(FunctionName) and then use the function FunctionName in C++. Like in the example above FindRoot is being used to solve the equation. It builds an equivalent chain of WS_ functions on runtime. The template function cast<T> can be sued to cast mathematica returned results back to C++ STL types.

symbol i("i"); // declare mathematica symbol i
value result_list; // declare the variable to hold the result
shell << Table(i, List(i, 1, 10)); // In Mathematica Table[i, {i, 1, 10}]
shell >> result_list;
std::cout << result_list << std::endl; // Prints List[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
std::cout << result_list->stringify() << std::endl; // Prints List[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
std::vector<int> list;
list = cast<std::vector<int>>(result_list);

shell.import("/path/to/package.m") can be used to import a mathematica package.

shell << Import("/path/to/package.m")` 

also yields the same as well. Because Import is also a mathametica function that can be declared using MATHEMATICA_DECLARE

I have tested it only on Linux and Mac platforms, but it should work on windows also. The Project is in Free BSD License.

mathematica++ gitlab repository | website | wiki