Convert Hex String to Hex Value

Question

I have a large hex string

abcdef...

and I want to convert it to

0xab 0xcd 0xef 

Are there any functions

Answer 1

Approximately the following (I wish I could made it shorter and use some library functions, any ideas?):

The function string_to_vector takes a character string and its length as input. It goes over the string, processing two characters (str[ i ] and str[ i + 1 ]) at a time. (For odd values of n, the last pass process only one character (str[ i ] though.) Each character is converted to numeric value using the hex_char_to_int method. Then it constructs a number by "joining" the two numeric values by shifting and adding. Finally, the constructed numeric value is appended to a vector of numeric values which is returned at the end of the function.

std::vector< unsigned >
string_to_vector( const char * str, size_t n ) {
    std::vector< unsigned > result;
    for( size_t i = 0; i < n; i += 2 ) {
        unsigned number = hex_char_to_int( str[ i ] ); // most signifcnt nibble
        if( (i + 1) < n ) {
            unsigned lsn = hex_char_to_int( str[ i + 1 ] ); // least signt nibble
            number = (number << 4) + lsn;
        }
        result.push_back( number );
    }
    return result;
}

The following function converts characters in the range [0-9A-Za-z] to the corresponding unsigned int value.

unsigned
hex_char_to_int( char c ) {
    unsigned result = -1;
    if( ('0' <= c) && (c <= '9') ) {
        result = c - '0';
    }
    else if( ('A' <= c) && (c <= 'F') ) {
        result = 10 + c - 'A';
    }
    else if( ('a' <= c) && (c <= 'f') ) {
        result = 10 + c - 'a';
    }
    else {
        assert( 0 );
    }
    return result;
}