Seems to skip if-statement

[aaronvan]

This code extracts the domain from an email address. The if-statement resolves to true; however, the variable at_index is not incremented. In fact, the program jumps right to the output commands. Using Visual Studio.

  int main(void) {
	std::string email = "[e-mail]";
	std::string domain = "";

	auto at_index = email.find('@');
	auto dot_index = email.rfind('.');

	if (at_index > -1 && dot_index > at_index) {
		++at_index;
		if (at_index < email.length() && at_index < dot_index) {
			int length = dot_index - at_index;
			domain = email.substr(at_index, length);
		}
	}
        std::cout << email << std::endl;
	std::cout << "domain is: " << domain << std::endl;

[Peter87]

I think the problem is that you are mixing signed and unsigned integers.

at_index is unsigned.
-1 is signed.

Before these two values can be compared they have to be converted to the same type. The compiler will therefore convert -1 to the unsigned type of at_index which results in the largest possible value of that type. No value can be larger than the largest possible value so the comparison will always result in false.

[dutch]

You presumably meant to compare to npos. And you should probably check dot_index, too.

	if (at_index != email.npos && dot_index != email.npos && dot_index > at_index) {

[aaronvan]

Lines 5 & 6: changed auto type to int and it works fine. Lesson learned: be wary of using auto with fundamental data types.

[dutch]

The actual lesson is to maximize your compiler warnings and don't ignore them. You should see one about comparing signed and unsigned, in both versions of your code. I showed you the proper fix. Do what you will, but you are relying on "undefined behavior" when setting an int to npos. Do you have a problem with npos?

BTW, C++ programmers don't say (void) for an empty parameter list. And there's no reason to initialize a string to "" since that's what it will be set to by its constructor.

[aaronvan]

Roger that, VS doesn't show the warning until I compiled it at warning level 3.

Main.cpp(13): warning C4018: '<': signed/unsigned mismatch
C:\Program Files (x86)\Microsoft Visual Studio\2019\...

I'll compile with max warnings in the future. I had to research npos (I'm brand-new to C++) and using it with the auto type. It works! Roger on the not string initializing and void w/empty parameter list.