How to test if a string contains any digits in C++

Question

I want to know if a string has any digits, or if there are no digits. Is there a function that easily does this?

Answer 1

given std::String s;

if( s.find_first_of("0123456789")!=std::string::npos )
//digits

Answer 2

find_first_of is probably your best bet, but I've been playing around with iostream facets so here's an alternative:

if ( use_facet< ctype<char> >( locale() ).scan_is( ctype<char>::digit,
      str.data(), str.data() + str.size() ) != str.data + str.size() )

Change string to wstring and char to wchar and you might theoretically have a chance at handling those weird fixed-width digits used in some Asian scripts.

Answer 3

#include <cctype>
#include <algorithm>
#include <string>

if (std::find_if(s.begin(), s.end(), (int(*)(int))std::isdigit) != s.end())
{
  // contains digit
}

Answer 4

There's nothing standard for the purpose, but it's not difficult to make one:

template <typename CharT>
bool has_digits(std::basic_string<CharT> &input)
{
    typedef typename std::basic_string<CharT>::iterator IteratorType;
    IteratorType it =
        std::find_if(input.begin(), input.end(),
                     std::tr1::bind(std::isdigit<CharT>,
                                    std::tr1::placeholders::_1,
                                    std::locale()));
    return it != input.end();
}

And you can use it like so:

std::string str("abcde123xyz");
printf("Has digits: %s\n", has_digits(str) ? "yes" : "no");

Edit:

Or even better version (for it can work with any container and with both const and non-const containers):

template <typename InputIterator>
bool has_digits(InputIterator first, InputIterator last)
{
    typedef typename InputIterator::value_type CharT;
    InputIterator it =
        std::find_if(first, last,
                     std::tr1::bind(std::isdigit<CharT>,
                                    std::tr1::placeholders::_1,
                                    std::locale()));
    return it != last;
}

And this one you can use like:

const std::string str("abcde123xyz");
printf("Has digits: %s\n", has_digits(str.begin(), str.end()) ? "yes" : "no");

Answer 5

boost::regex re("[0-9]");
const std::string src = "test 123 test";
boost::match_results<std::string::const_iterator> what; 
bool search_result = 
   boost::regex_search(src.begin(), src.end(), what, re, boost::match_default);

Answer 6

Perhaps the following:

if (std::string::npos != s.find_first_of("0123456789")) {
  std::cout << "digit(s)found!" << std::endl;
}