C/C++ question

[Thirumalesh]

Hi,
I have a string like this:

"4f020098e567"

I need to read that string char by char and concatinate each two char's to form a byte to get hexadecimal value. I know we can use shift operators to do this. Is there any simplest way to do.

Thanks,
Thiru

[NMTop40]

I don't know how you'd do it using shift parameters but..

std::string s("4f020098e567");
std::vector< BYTE > vectByte;
int len = s.size();
int pos;
char *stop; // required for later
if ( len & 1 ) // odd length so insert leading 0
{
s.insert( 0, 1, '0' );
len++;
}
vectByte.resize( len / 2 );

for ( pos=0; pos < len; pos += 2 )
{
std::string sub( s, spos, 2 ); // gets sub string
vectPos[ pos / 2 ] = (BYTE)strtoul( sub.c_str(), &stop, 16 );
}

[NMTop40]

you need some more commentary?

std::string s("4f020098e567"); // s is the string to convert
std::vector< BYTE > vectByte; // this gives an array of variable length of the bytes
int len = s.size(); // get the length of the string
int pos; // required to run through the string
char *stop; // required for second parameter of strtoul
/*
we are going to run through 2 characters at a time
if our length is odd, there will be a spare one
at the end. We could report this as an error but
let's fix it and put in a leading zero
*/
if ( len & 1 )
{
s.insert( 0, 1, '0' ); // puts an extra '0' character at the front of string
len++; // which increases its length by 1
}
vectByte.resize( len / 2 ); // set the size of our byte array - half the length

for ( pos=0; pos < len; pos += 2 )
{
std::string sub( s, spos, 2 ); // gets sub string of 2 characters
/*
now the bit we have been leading up to - use the
strtoul function with base 16. This will convert our string (substring of 2 characters) to
an unsigned long. It will be between 0 and 255.
*/
vectPos[ pos / 2 ] = (BYTE)strtoul( sub.c_str(), &stop, 16 );
}



Now the array vectPos will contain 6 bytes as follows:
[0]: 0x4f (79)
[1]: 0x02 (2)
[2]: 0x00 (0)
[3]: 0x98 (152)
[4]: 0xe5 (229)
[5]: 0x67 (103)


I assume that is what you wanted

[Thirumalesh]

I am using CString, Is it ok, or it need any modifications.
-Thiru

[NMTop40]

modifications with CString (note this is not the MFC forum but we know CString here anyway)

1. s.Insert(0, '0');
2. CString sub = s.Mid( pos, 2 );
3. No need to put in c_str(), you can pass the CString sub directly to strtoul




You an also use CArray< UCHAR, UCHAR > instead of std::vector, but it has the disadvantage of not being copyable, so you have to pass one in by reference to be modified, or stick with std::vector.

If you use CArray, it is SetSize() not resize()

[Thirumalesh]

Thanks