Input validation using character array in C++

Question

I am creating a C++ program to validate book name using a function in c++. The function must return 1 if the input is valid and 0 if the input is invalid. Book name can only contain upper case, lower case characters, color(:), comma(,) and space (there should be no consecutive spaces, commas, and colons). And the maximum characters in a character array is 60.

I tried the following way but I am not getting the desired answer.

const int MAX_BOOK_NAME = 60;

bool isValidBookName(char bookName[MAX_BOOK_NAME])
{
     int length = strlen(bookName);
     if (length > 59)
     {
          return false;
     }

     for (int i = 0; i < 59; i++)
     {
          if (bookName[i] < 'A' || bookName[i] > 'Z' || bookName[i] < 'a' || bookName[i] > 'z' || bookName[i] != '  ' || bookName[i] != ':' || bookName[i] != ',')
          {
               return false;
          }
     }

     return true;
}

int main()
{
     char arr[60];
     cout << "Please Enter Your Book Id : ";
     cin.getline(arr, 60);
     cout << "Your Entered Name is " << isValidBookName(arr) << endl;
}

If length > 59 is true, then you're already in trouble as that would mean the buffer is overflowed and you already have undefined behavior because of that. — Some programmer dude
– Some programmer dude, Commented Jan 13, 2020 at 14:24
I also suggest you take a look as the std::isalpha function, as your way to check for letters is encoding-specific and C++ doesn't assume any specific encoding. — Some programmer dude
– Some programmer dude, Commented Jan 13, 2020 at 14:25
And the loop for (int i = 0; i < 59; i++) disregard the string null terminator, and could go out into uninitialized areas of the array which lead to undefined behavior. — Some programmer dude
– Some programmer dude, Commented Jan 13, 2020 at 14:26
"I tried the following way but I am not getting the desired answer. " Please provide expected input and expected output — AndyG
– AndyG, Commented Jan 13, 2020 at 14:28

eerorika · Accepted Answer · 2020-01-13 14:38:26Z

2

bookName[i] < 'A' || bookName[i] > 'Z' || bookName[i] < 'a' || bookName[i] > 'z'

These checks match every character because for example (assuming ASCII or compatible encoding) all capital letters match the condition bookName[i] < 'a' and all smaller case letters match bookName[i] > 'Z'. Since these checks are used to match an invalid character, the check is wrong.

std::isalpha can simplify your program greatly, as pointed out in comments.

edited Jan 13, 2020 at 14:38

answered Jan 13, 2020 at 14:28

eerorika

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Comments

Some programmer dude · Accepted Answer · 2020-01-13 14:29:35Z

1

The logic of your character check is flawed.

The requirement in your question is that each character must be a letter, or a comma, or a colon, or ... etc. The reverse of that is not "not a letter or not a comma or not a colon or ... etc." The reverse is "not a letter and not a comma and not a colon and ... etc."

answered Jan 13, 2020 at 14:29

Some programmer dude

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