How do I use try…catch to catch floating point errors?

Question

I\'m using c++ in visual studio express to generate random expression trees for use in a genetic algorithm type of program.

Because they are random, the trees often

Answer 1

The C++ runtime environment won't help you the slightest here. You have to perform these checks yourself, explicitly in your code. Unless of course the functions you're calling are doing these checks -- in which case it depends on how they behave in the case of an error.

Let me explain:

double divide(double a, double b) {
    return a / b;  // undefined if b is zero
}

Should be in fact

double divide(double a, double b) {
    if( b == 0 ) {
        // throw, return, flag, ...  you choose how to signal the error
    }
    return a / b;  // b can't possibly be zero here
}

If the code that fails on divide-by-zero and such isn't yours then you'll have to dig deeper to find what it does in the case of a threat for an error. Does it throw? Set a flag? Ask the author and/or read the source.

Here's an example for an exception:

struct bad_value : public std::exception { };

double divide(double a, double b) {
    if( b == 0 ) throw bad_value("Division by zero in divide()");
    return a / b;  // b can't possibly be zero here
}

// elsewhere (possibly in a parallel universe) ...

    try {
        double r1 = divide(5,4);
        double r2 = divide(5,0);
    } catch( bad_value e ) {
        // ...
    }