How to read the nth number from a string of numbers?

[mosei168m]

How do i read the nth number in a string of n numbers separated by whitespace like the following.

112857 2498 4417878 1854672 417483 472422 37028136 7924624 0 2444476 9779560

The following numbers are from the /sys/block/sda/stat file on my Linux system.
I was thinking off using a stringstream object and writing the numbers into an integer a number of times before getting to the right count, but i'm not sure if this is the best way.

Thanks in advance.

[JLBorges]

An other option is to use a regular expression to capture the nth number.

long long nth_number( std::string text, std::size_t n ) // for first number, n == 1
{
    // (?:\d+\s+){4}
    //            \d+ one or more digits followed by
    //            \s+ one ore more white space characters
    // (?:)   do not capture
    // {4}    repeated exactly four times
    //
    // (\d+)  one or more digits, capture (numbered capture group 1)
    //
    // .*     zero or more characters
    const std::regex pattern( "(?:\\d+\\s+){" + std::to_string(n-1) + "}(\\d+).*" ) ;
    std::smatch results ;
    if( std::regex_match( text, results, pattern ) ) return std::stoll( results[1] ) ;
    else throw std::invalid_argument( "no match for nth number" ) ;
}

http://coliru.stacked-crooked.com/a/80f0710b296e883e

[mosei168m]

Cool! I new regex was the answer, I'm just not familiar with ECMAScript syntax. Thanks a bunch!

[JLBorges]

Modified ECMAScript is the default (the one used if no syntax option is specified).
The standard regular expressions library also supports basic/extended posix, awk, grep and egrep syntax options.
http://en.cppreference.com/w/cpp/regex/syntax_option_type