What is the difference between string::at and string::operator[]?

Question

I was taught string::at in school, but by exploring the string library I saw string::operator[], which I was never shown before.

I\'m now u

Answer 1

Yes, there is one major difference: using .at() does a range check on index passed and throws an exception if it's over the end of the string while operator[] just brings undefined behavior in that situation.

Answer 2

std::string::at

Returns a reference to the character at specified location pos. Bounds checking is performed, exception of type std::out_of_range will be thrown on invalid access.

string::operator[]

Returns a reference to the character at specified location pos. No bounds checking is performed. It's undefefined behavior to access out-of-boundary with operator[].

string::operator[] should be silghtly faster than std::string::at

see the reference

Answer 3

at does bounds checking, exception of type std::out_of_range will be thrown on invalid access.

operator[] does NOT check bounds and thus can be dangerous if you try to access beyond the bounds of the string. It is a little faster than at though.