#include <iostream>
#include <string>
#include <vector>
#include <sstream>
#include <limits>
#include <exception>

std::vector<unsigned char> foo( const std::string& str )
{
    std::vector<unsigned char> ret;

    std::istringstream is( str );
    for( int val; is>>std::hex>>val; )
    {
        if( val<std::numeric_limits<unsigned char>::min() || val>std::numeric_limits<unsigned char>::max() )
            throw std::domain_error( "fuck" );

        ret.push_back( val );
    }
    if( !(is>>std::ws).eof() )
        throw std::domain_error( "shit" );

    return ret;
}

int main( void )
{
    try {
        std::vector<unsigned char> arr = foo( "FF FF FF FF FF FF FF FF" );

        for( size_t i=0; i!=arr.size(); ++i )
            std::cout << (int)arr[i] << ' ';
    }
    catch( std::exception& e ) {
        std::cerr << e.what() << '\n';
        return 1;
    }
}