Question

I’m currently working with the Diab 4.4 C++ compiler. It’s a total POS, non ANSI-compliant, and I’ve found problems with it in the past.

I’m wondering if the following problem is an issue with the compiler, or a shortcoming in my knowledge of C++

I realize that the form of x = x && y; will short-circuit the y part if x is false. What the compiler is doing is short-circuiting in the case of x = x && y(); where y() is a non-const function.

class A
{
int _a;
A(int a) { _a = a; }
bool someFunction() { _a = 0; return true; } 
};

main(...)
{
A obj = A(1);
bool retval = false;

retval = retval && A.someFunction();

/* What is the value of A._a here? */
}

What seems wrong to me is the fact that the compiler is doing this short-circuiting even though someFunction() is not a const function. If it’s not const, is the compiler overstepping its bounds by skipping A.someFunction() when retval is false?

Also, I realize this issue can be avoided by writing retval = A.someFunction() && retval; but I’d really like to know why this is happening.

Answer 1

The && and || operators are defined to evaluate lazily, this is the way the language works. If you want the side effects to always happen, invoke the function first and stash the result, or refactor the function to split the work from the state query.