C++: Validating a string with a multitude of conditions

Question

I'm trying to write validation for a string that follow the following guidelines:

1. Can be alphabet

2. Can be '.' or ','

3. Can have a space

4. CAN'T be blank

So for example, "Bob", "Bob Smith", and "Bob Smith, Jr." should be fine, while " " or just hitting the enter key shouldn't.

If the string follows these guidelines the function should simply return it, but if it doesn't it should continue looping through until a correct entry is entered.

I've tried a few different ways of looping through to validate, and if I'm understanding break correctly, I believe this structure should work. That said, entering a simple string such as "Bob" is failing the tests. I'm also unsure how to make sure the user can't just hit the space bar or press enter.

std::string patronName()
    {
        std::string name;
        bool loopFlag = true;

        do
        {
            std::cout << "Please enter the name of the Patron: ";
            std::getline(std::cin, name);

            for (int i = 0; i < name.length(); i++)
            {
                if (!isalpha(name[i]) || !ispunct(name[i]) || !isspace(name[i]) || name.empty())
                {
                    std::cout << "Invalid name entry." << std::endl;
                    break; //If we're invalid, doesn't matter what the rest is
                }
                loopFlag = false;
            }

        }
        while(loopFlag);

        return name;
    }

Are there any obvious errors I'm missing in my logic?

Answer 1

If char is not a alpha or it is not puctuation or it is not a spece then it is invalid.

The letter c is not a space therefore your condition is met.

Try && instead of ||. If char is not a alpha AND it is not puctuation AND it is not a space then it is invalid.

I would look at refactoring your code to separate the validation from other code.

bool isValid(const std::string& str)
{
    // Assume the string is valid - up to us to prove it is not...
    bool result = true;
    // Assume the stringis all spaces - up to us to mark when we see a valid non whitespace
    bool allSpaces = true;

    size_t len = str.length();
    for(size_t i = 0; i < len; i++)
    {
        unsigned char ch = (unsigned char)str[i];
        // alpha and punctuation are ok and mean that the string has
        // something other than a space.
        if (isalpha(ch) || ispunct(ch))
        {
          allSpaces = false;
          continue;
        }
        // space is ok - as long as we have something else too...
        if (isspace(ch))
        {
            continue;
        }
        // not a space, allowed punctuation or an alpha ?
        // must be an error!
        result = false;
        break;
    }
    if (allSpaces)
    {
        result = false;
    }
    return result;
}

See This answer for information on why cast to unsigned char is recommended.