Why cannot I find a number by regular expression?

[Observer]

Hello

Why cannot I find a number by regular expression?

#include <regex>
#include <string>
#include <iostream>

int main()
{
    std::string str = "Hello my 5 compluter!";

    try {
        const std::regex e( "\d", std::regex_constants::basic );
        std::sregex_iterator next( str.begin(), str.end(), e );
        std::sregex_iterator end;
        while ( next != end ) {
            std::smatch match = *next;
            std::cout << match.str() << "\n";
            next++;
        } 
    } catch ( const std::regex_error &e ) {
        std::cerr << "Error: incorrect regular expression" << std::endl;
        return 1;
    }

    return 0;
}

[Zhuge]

It works for be if I remove the std::regex_constants::basic argument and escape the backslash ('\d' is being interpreted as an escape code, like '\n').

[Observer]

Thank you very much! It works now!

#include <regex>
#include <string>
#include <iostream>

int main()
{
    std::string str = "Hello my 5 compluter!";

    try {
        const std::regex e( "\\d" );
        std::sregex_iterator next( str.begin(), str.end(), e );
        std::sregex_iterator end;
        while ( next != end ) {
            std::smatch match = *next;
            std::cout << match.str() << "\n";
            next++;
        } 
    } catch ( const std::regex_error &e ) {
        std::cerr << "Error: incorrect regular expression" << std::endl;
        return 1;
    }

    return 0;
}