C++ char array value assignment

Question

I'm trying to keep the alphabet in a char array. But 4 letters show absurd charachters.

I run the program step by step using F11 button. Wrote the alphabet and after 'Q', until 'V' whatever I write, it shows ...PQÿÿÿÿVWXYZ this character: 'ÿ'

    int main()
    {   
    cout << "ALPHABET:";
    char alf[] = "";
    cin >> alf;
        system("PAUSE");
    }

I expect: ABCDEFGHIJKLMNOPQRSTUVWXYZ

Actual result: ABCDEFGHIJKLMNOPQÿÿÿÿVWXYZ

Slava · Accepted Answer · 2018-12-21 14:41:02Z

1

Problem is with this line:

char alf[] = "";

you declare char array with size 1 which can only hold empty strings (null terminator). Note that std::istream::operator>> with char * does not validate size of array (it cannot) so you are getting Undefined Behavior writing into array with out of bounds. Solution is to use std::string instead which will grow as needed.

int main()
{   
    std::cout << "ALPHABET:";
    std::string alf;
    std::cin >> alf;
    std::cout << alf << std::endl;
}

answered Dec 21, 2018 at 14:41

Slava

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10 Comments

Slava Over a year ago

It probably should be at least 27 as you need null terminator, but I would not recommend to use char array with >> as it leads to unsafe programs that vulnerable to buffer overflow, do not make such habit.

Ömer Faruk Sarıışık Over a year ago

I have a function which has a parameter char*. So I can't use string

SergeyA Over a year ago

@Slava - correction. It (operator>>) could have a separate overload for C-style arrays. It doesn't, though.

SergeyA Over a year ago

@ÖmerFarukSarıışık you should be able to use std::string and pass those functions the pointer to underlying char buffer you can get with c_str()

Slava Over a year ago

@SergeyA even with that overload it would only work in some cases, anyway lets say it cannot in the form it is written.

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