vector::at vs. vector::operator[]

Solution 1:

I'd say the exceptions that vector::at() throws aren't really intended to be caught by the immediately surrounding code. They are mainly useful for catching bugs in your code. If you need to bounds-check at runtime because e.g. the index comes from user input, you're indeed best off with an if statement. So in summary, design your code with the intention that vector::at() will never throw an exception, so that if it does, and your program aborts, it's a sign of a bug. (just like an assert())

Solution 2:

it forces me to wrap it with try-catch block

No it doesn't (the try/catch block can be upstream). It is useful when you want an exception to be thrown rather than your program to enter undefined behavior realm.

I agree that most out of bounds accesses to vectors are a programmer's mistake (in which case you ought to use assert to locate those mistakes more easily; most debug versions of standard libraries do this automatically for you). You do not want to use exceptions that can be swallowed upstream to report programmer mistakes: you want to be able to fix the bug.

Since it is unlikely that an out of bounds access to a vector is part of the normal program flow (in the case it is, you're right: check beforehand with size instead of letting the exception bubble up), I agree with your diagnostic: at is essentially useless.