How can I check if a string has special characters in C++ effectively?

Question

I am trying to find if there is better way to check if the string has special characters. In my case, anything other than alphanumeric and a \'_\' is considered a special charac

Answer 1

If you want this, but don't want to go the whole hog and use regexps, and given you're test is for ASCII chars - just create a function to generate the string for find_first_not_of...

#include <iostream>
#include <string>

std::string expand(const char* p)
{
    std::string result;
    while (*p)
        if (p[1] == '-' && p[2])
        {
            for (int c = p[0]; c <= p[2]; ++c)
                result += (char)c;
            p += 3;
        }
        else
            result += *p++;
    return result;
}

int main()
{
    std::cout << expand("A-Za-z0-9_") << '\n';
}

Answer 2

The first thing that you need to consider is "is this ASCII only"? If you answer is yes, I would encourage you to really consider whether or not you should allow ASCII only. I currently work for a company that is really having some headaches getting into foreign markets because we didn't think to support unicode from the get-go.

That being said, ASCII makes it really easy to check for non alpha numerics. Take a look at the ascii chart.

http://en.wikipedia.org/wiki/ASCII#ASCII_printable_characters

• Iterate through each character
• Check if the character is decimal value 48 - 57, 65 - 90, 97 - 122, or 95 (underscore)

Answer 3

Using

    s.erase(std::remove_if(s.begin(), s.end(), my_predicate), s.end());

    bool my_predicate(char c)
    {
     return !(isalpha(c) || c=='_');
    }

will get you a clean string s.

Erase will strip it off all the special characters and is highly customisable with the my_predicate function.