C++ compatability

C* is not backward-compatible with C++ or C. However, since it is translated to C++, there are special features that allow programmers to use C++ code, including the standard library, with C* code.

Say you have a C++ file - such as <cmath> from the standard library - and you want to use a function from it. Let's take the sqrt function as an example. It can be included in a program as follows:

cpp {
	include <cmath>
	function sqrt(double x) => double;
}


function main() => int {
	<< sqrt(4);
}

The cpp block is used to include C++ header (or source) files, which is done with an "include" statement. include works like #include from C++. The code from the included file is included verbatim in the output, and does not go through the C* translator. However, the C* code still needs to know about any symbols it's using from the included file, so those symbols must be declared, in C* syntax, within the cpp block (sqrt above is declared as such). Putting a declaration in a cpp block simply means "don't include this declaration in the C* translator output", which is what the programmer needs, since sqrt is already declared in the <cmath> header. Without the declaration of sqrt in C* syntax, the call to it in main would fail to typecheck, because the C* compiler can't look in the <cmath> header to find C++ declarations.

Remember that if you have your own C++ header and accompanying source file, you would have to link the source file with your final program if you use the header in a cpp block.

Though the eventual goal is for C* to have its own libraries, in the meantime there is a lot of C/C++ code in the world, and the ability to use those libraries until there is more C* code should make C* a lot more useful. Of course, there is the added annoyance of having to declare the symbols you're using, which means it may not be worthwhile to rely too much on C++ symbols. Also note that, since C* doesn't yet have classes, you can't make use of C++ classes directly, but must wrap their use in C++ functions.

Though it would be technically possible to take the C++ result from the C* compiler and use it in a C++ program, doing so is not recommended, because the C* compiler is allowed to output whatever equivalent C++ code it wants.