c++ string vs. c string

This is a discussion on c++ string vs. c string within the C++ Programming forums, part of the General Programming Boards category; Hello guys I have a dns reply parser, which is written in c code.. The reply is in binary, so ...

  1. #1
    l2u
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    c++ string vs. c string

    Hello guys

    I have a dns reply parser, which is written in c code.. The reply is in binary, so parsing data is a little different as normally.. I wonder if would it be easier/better to use c++ string instead of char and char pointers for processing data?

    Im used to char *p = sth; sth++; etc..

    Heres the example of a function so you get a better idea what I'm doing..

    Code:
    int decodehostname(char *buf, char *packet, unsigned int len, unsigned int pos) {
    	unsigned int label;
    	int bufpos = 0, r = 0;
    
    restart:
    	while(pos < len) {
    		label = packet[pos++];
    
    		if (label & 0xC0) {
    			if (pos >= len) return 0;
    			label = ((label & 0x3F) << 8) | packet[pos++];
    
    			if (r == 0) r = pos;
    			pos = label;
    
    			goto restart;
    		}
    		//printf("   bufpos: %d pos: %d label: %d\n   len: %d\n", bufpos, pos, label, len);
    		if (label == 0)
    			break;
    
    		//check
    		if (bufpos + label + 1 >= 128) return 0;
    		if (pos + label > len) return 0;
    
    		memcpy(buf + bufpos, packet + pos, label);
    		pos += label;
    		bufpos += label;
    		buf[bufpos++] = '.';
    	}
    	if (bufpos) bufpos--;
    	buf[bufpos] = 0;
    
    	return (r ? r : pos);
    }
    Thanks for help again

  2. #2
    System Novice siavoshkc's Avatar
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    Code:
    int decodehostname(string &buf, string &packet, unsigned int len, unsigned int pos) {
          unsigned int label;
          int bufpos = 0, r = 0;
    
          while(pos < len) {
                label = packet[pos++];
    
                if (label & 0xC0) {
                      if (pos >= len) return 0;
                      label = ((label & 0x3F) << 8) | packet[pos++];
    
                      if (r == 0) r = pos;
                      pos = label;
    
                      continue;
                }
                //printf("   bufpos: %d pos: %d label: %d\n   len: %d\n", bufpos, pos, label, len);
     if (label == 0)
                      break;
    
                //check
     if (bufpos + label + 1 >= 128) return 0;
                if (pos + label > len) return 0;
    
                string part = packet.substr(pos, label);
                buf.replace(bufpos, part.length() ,part );
                pos += label;
                bufpos += label;
                buf[bufpos++] = '.';
          }
          if (bufpos) bufpos--;
          buf[bufpos] = 0;
    
          return (r ? r : pos);
    }
    Last edited by siavoshkc; 09-15-2006 at 10:20 AM.
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  3. #3
    Frequently Quite Prolix dwks's Avatar
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    It's usually easier to use the C++ string class than C strings. They can do everything C arrays can, and if you need a C string you can use the .c_str() member function (which returns a const char *; if you need a modifiable C string then you need to use one).
    dwk

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