I always thought if I accessed an array index greater than the array size that it would cause a runtime error? But it seems to be happy to run and output zero. Is this compiler specific or OS specific? Will some different environments cause a runtime error when you access an array index greater than the array size?
For eg;
int foo[5];
cout << foo[5] << endl;
vector<int> bar(5);
cout << bar[5] << endl;
Accessing an array outside its bounds it's not a runtime error in C++: it's undefined behavior and it means that anything can happen, including nothing.
In C++ there are no "runtime error angels", only "undefined behavior daemons".
Well, the code you provided is a classic example of undefined behaviour.
I always thought if I accessed an array index greater than the array size that it would cause a runtime error?
The vector class' .at(size_type pos) method performs a boundary check and throws std::out_of_range if pos is not within the range of the container.
it's undefined behavior trying to read or write beyond the bounds of the array , if it is a dynamic array the program may crash.
char c1[] = "123";
char c2[2] = "A"; // ok c2[0] = 'A', c2[1] = '\0';
cout << c1 << endl; // 123 ok
cout << c2 << endl; // A ok
c2[5] = 'M'; // writing to the out bound of the array
cout << c1 << endl; // 1M3 ??!!
cout << c2 << endl; // A ok
it causes memory dongling here.
