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copied!<p>There are several approaches possible. The simplest and the most portable is to break the characters down into two character <code>std::string</code>, using each to initialize an <code>std::istringstream</code>, set up the correct format flags, and read the value from that. A somewhat more efficient solution would be to create a single string, inserted whitespace to separate the individual values, and just use one <code>std::istringstream</code>, something like: </p> <pre><code>std::vector<uint8_t> convert4UChars( std::string const& in ) { assert( in.size() >= 8 ); std::string tmp( in.begin(), in.begin() + 8 ); int i = tmp.size(); while ( i > 2 ) { i -= 2; tmp.insert( i, 1, ' '); } std::istringstream s(tmp); s.setf( std::ios_base::hex, std::ios_base::basefield ); std::vector<int> results( 4 ); s >> results[0] >> results[1] >> results[2] >> results[3]; if ( !s ) { // error... } return std::vector<uint8_t>( results.begin(), results.end() ); } </code></pre> <p>If you really want to do it by hand, the alternative is to create a 256 entry table, indexed by each character, and use that:</p> <pre><code>class HexValueTable { std::array<uint_t, 256> myValues; public: HexValueTable() { std::fill( myValues.begin(), myValues.end(), -1 ); for ( int i = '0'; i <= '9'; ++ i ) { myValues[ i ] = i - '0'; } for ( int i = 'a'; i <= 'f'; ++ i ) { myValues[ i ] = i - 'a' + 10; } for ( int i = 'A'; i <= 'A'; ++ i ) { myValues[ i ] = i - 'a' + 10; } } uint8_t operator[]( char ch ) const { uint8_t results = myValues[static_cast<unsigned char>( ch )]; if ( results == static_cast<unsigned char>( -1 ) ) { // error, throw some exceptions... } return results; } }; std::array<uint8_t, 4> convert4UChars( std::string const& in ) { static HexValueTable const hexValues; assert( in.size() >= 8 ); std::array<uint8_t, 4> results; std::string::const_iterator source = in.begin(); for ( int i = 0; i < 4; ++ i ) { results[i] = (hexValues[*source ++]) << 4; results[i] |= hexValues[*source ++]; } return results; } </code></pre>

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