Question

//SECTION I:
void main()
{
    char str[5] = "12345";  //---a)
    char str[5] = "1234";   //---b)
    cout<<"String is: "<<str<<endl;
}
Output: a) Error: Array bounds Overflow.
        b) 1234

//SECTION II:
void main()
{
    char str[5];
    cout<<"Enter String: ";
    cin>>str;
    cout<<"String is: "<<str<<endl;
}

I tried with many different input strings, and to my surprise, I got strange result:

Case I: Input String: 1234, Output: 1234 (No issue, as this is expected behavior)

Case II: Input String: 12345, Output: 12345 (NO error reported by compiler But I was expecting an Error: Array bounds Overflow.)

Case III: Input String: 123456, Output: 123456 (NO error reported by compiler But I was expecting an Error: Array bounds Overflow.)

………………………………………….

………………………………………….

Case VI: Input String: 123456789, Output: 123456789(Error: unhandeled exception. Access Violation.)

My doubt is, When I assigned more characters than its capacity in SECTION I, compiler reported ERROR: Array bounds Overflow.

But, when I am trying the same thing in SECTION II, I am not geting any errors. WHY it is so ?? Please note: I executed this on Visual Studio

Answer 1

char str[5] = "12345";

This is a compiletime error. You assign a string of length 6 (mind the appended null-termination) to an array of size 5.

---

char str[5];
cin>>str; 

This may yield a runtime error. Depending on how long the string is you enter, the buffer you provide (size 5) may be too small (again mind the null-termination).

---

The compiler of course can’t check your user input during runtime. If you’re lucky, you’re notified for an access violation like this by Segmentation Faults. Truly, anything can happen.

Throwing exceptions on access violations is not mandatory. To address this, you can implement array boundary checking yourself, or alternatively (probably better) there are container classes that adapt their size as necessary (std::string):

std::string str;
cin >> str;