Converting Hex Characters to readable ASCII

[kbomb987]

When you receive a GET from a web browser, the parameters come encoded in Hex character format. Is there an MFC function to convert the hex characters to readable ascii characters, or do I have to manually write a switch() statement to parse the hex chars into ascii? If so, anyone already written one?

Thanks.

www.DummySoftware.com

[Erik Bergman]

some error checking may be added ( excuse typos or it doesn't work
but you could do something like this :

use:


unsigned char HexToChar( char * ptrtohex );

int main()
{
char hex[] = "AB";
printf("%s is %d", HexToChar( hex ) );
}

unsigned char HexToChar( char * ptrtohex )
{
unsigned char ret;
if( ptrtohex[0] >= 'A' && ptrtohex[0] <= 'F' )
ret = (ptrtohex[0]-'A' + 10) << 4;
else if( ptrtohex[0] >= 'a' && ptrtohex[0] <= 'f' )
ret = (ptrtohex[0]-'a' + 10) << 4;
else if( ptrtohex[0] >= '0' && ptrtohex[0] <= '9' )
ret = (ptrtohex[0]-'0') << 4;

if( ptrtohex[1] >= 'A' && ptrtohex[1] <= 'F' )
ret = ret | ( ptrtohex[1]-'A' +10 );
else if( ptrtohex[1] >= 'a' && ptrtohex[1] <= 'f' )
ret = ret | ( ptrtohex[1]-'a' +10);
else if( ptrtohex[1] >= '0' && ptrtohex[1] <= '9' )
ret = ret | (ptrtohex[1]-'0');

return ret;
}

[kbomb987]

I compiled it up real quick and got an Unhandled Exception.
What exactly are you passing in there - a single character? Or a set of
characters that make up a hex character to be converted into an ascii character?

When the browser passes you the string with all those hex characters, you would need to send something like 2 or 3 characters to your function for it to convert it. Something like :

Here+is+some+stuff%0D%0A

Where the %0D is a \r
%0A is a \n

And there are 3 characters in total. Any ideas on modifying that code?


www.DummySoftware.com

[kbomb987]

Hey, I got it working.. works great! Thanks a lot. Here is some extra work done to it to perfectly convert a web GET query (including spaces) with hex characters to a full string using the previous HexToChar function, in case anyone else out there has this problem:


// Help function converts a Hex character consisting
// of 2 characters ptrtohex[2] to an ASCII character.
unsigned char HexToChar( char * ptrtohex )
{
unsigned char ret;
if( ptrtohex[0] >= 'A' && ptrtohex[0] <= 'F' )
ret = (ptrtohex[0]-'A' + 10) << 4;
else if( ptrtohex[0] >= 'a' && ptrtohex[0] <= 'f' )
ret = (ptrtohex[0]-'a' + 10) << 4;
else if( ptrtohex[0] >= '0' && ptrtohex[0] <= '9' )
ret = (ptrtohex[0]-'0') << 4;

if( ptrtohex[1] >= 'A' && ptrtohex[1] <= 'F' )
ret = ret | ( ptrtohex[1]-'A' +10 );
else if( ptrtohex[1] >= 'a' && ptrtohex[1] <= 'f' )
ret = ret | ( ptrtohex[1]-'a' +10);
else if( ptrtohex[1] >= '0' && ptrtohex[1] <= '9' )
ret = ret | (ptrtohex[1]-'0');

return ret;
}

// Converts a CString (usually obtainined through a GET query to the browser
// and converts any %Hex characters or + spaces
// into its ASCII equivelent and returns a CString.
CString HexToString(CString strDecoded)
{
int ndx = 0;

// change all '+' to ' '
while( (ndx=strDecoded.Find('+')) != -1 )
strDecoded = strDecoded.Left(ndx) + ' ' + strDecoded.Mid(ndx+1);

// first see if there are any %s to decode....
if ( strDecoded.Find( '%' ) != -1 )
{
// iterate through the string, changing %dd to special char....
for( ndx=0; ndx < strDecoded.GetLength(); ndx++ )
{
char ch = strDecoded.GetAt( ndx );
if ( ch == '%' )
{
if ( strDecoded.GetAt( ndx+1 ) == '%' )
{
// wanna keep one percent sign....
strDecoded = strDecoded.Left(ndx) + strDecoded.Mid(ndx+1);
}
else
{
// assume we have a hex value....
char ch1 = strDecoded.GetAt(ndx+1);
char ch2 = strDecoded.GetAt(ndx+2);
char chs[3];
chs[0] = ch1;
chs[1] = ch2;
CString oldstr = strDecoded;
strDecoded = strDecoded.Left(ndx);
strDecoded += HexToChar((char*)chs);
strDecoded += oldstr.Mid(ndx+3);
}
}
}
}

return strDecoded;
}




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