CODEWITHSUNDEEP
c++
Shyam
Shyam

Reputation: 89

How to iterate a string in which was read without knowing its size?

Is char s[] = "" advisable to read a string without knowing its size? 

char s[] = "";
cin >> s;
cout << s[2];  // this is working
int k = 2;
cout << s[k]; // while this does not

Any ideas?

Upvotes: 0

Views: 75

Answers (2)

Joseph Thomson
Joseph Thomson

Reputation: 10403

You are creating a char array of length 1, containing the character '\0'. If cin writes anything other than an empty string to s, it will overflow the bounds of the array, causing undefined behaviour. Do not use cin with arrays; use string instead.

string s;
cin >> s;

Then, you must check that the character index you use is in-bounds, or you will get undefined behaviour again.

if (k < s.size()) {
    cout << s[k];
}

So no, it is not safe to access an array (or string) without knowing its size.

Upvotes: 2

Paul Floyd
Paul Floyd

Reputation: 6916

's' is an array of 1 char. When you read from cin, anything beyond the first character writes beyond the allocated size of 's', which leads to undefined behaviour. It could well be that the 'beyond' part is actually in 'k', which would work for the first cout, but then fail after k has been initialized for the second cout.

Upvotes: 1

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