execute C++ from String variable

Question

it is possible in C++ to execute the C++ code from string variable. Like in Javascript:

var theInstructions = "alert('Hello World'); var x = 100";

var F=new Function (theInstructions);

return(F());

I want something very similar like Javascript in C++. How to do that ?

Answer 1

No, C++ is a static typed, compiled to native binary language.

Although you could use LLVM JIT compilation, compile and link without interrupting the runtime. Should be doable, but it is just not in the domain of C++.

If you want a scripting engine under C++, you could use for example JS - it is by far the fastest dynamic solution out there. Lua, Python, Ruby are OK as well, but typically slower, which may not be a terrible thing considering you are just using it for scripting.

For example, in Qt you can do something like:

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    QScriptEngine engine;
    QScriptValue value = engine.evaluate("var a = 20; var b = 30; a + b");

    cout << value.toNumber();

    return a.exec();
}

And you will get 50 ;)

Answer 2

You will need to invoke a compiler to compile the code. In addition, you will need to generate some code to wrap the string in a function declaration. Finally, you'll then somehow need to load the compiled code.

If I were doing this (which I would not) I would:

1. Concatenate a standard wrapper function header around the code
2. Invoke a compiler via the command line (system()) to build a shared library (.dll on windows or .so on linux)
3. Load the shared library and map the function
4. Invoke the function

This is really not the way you want to write C code in most cases.