c++ - Is there a way to prepend a fixed number of bytes before a std:: stringbuf? -


i’m trying prepend 4 byte header existing std::stringbuf object. example if data in stringbuf ‘h’,’e’,’l’,’l’,’o’ , header ‘0x00’,’0x10’, ‘0x00’,’0x0a’ need change stringbuf ‘0x00’,’0x10’, ‘0x00’,’0x0a’, ‘h’,’e’,’l’,’l’,’o’. i’ve been trying below approach inefficent because has 3 copies of data in sbuf, textstream , buff. using new char[] more problematic because needs continuous block of memory , can have large streams.

can me showing me how can in better optimized way? mean there way prepend bytes before existing stringbuf?

std::stringbuf createstreamwithheader(std::stringbuf &sbuf) {     int = sbuf.str().size();     std::stringbuf textstreambuf;     uint32_t streamsize = sbuf.str().size();     char* buff = new char [streamsize + 5]; //using char buffer not memory efficient needs big contonuous chunk of memory.      zeromemory(buff, (streamsize + 5)*sizeof(char));      buff[0] = (streamsize >> 24) & 0xff; //in case header needs contain size of data in sbuf     buff[1] = (streamsize >> 16) & 0xff;     buff[2] = (streamsize >> 8) & 0xff;     buff[3] = (streamsize >> 0) & 0xff;     strcpy(&buff[4], sbuf.str().c_str()); //strcpy not right solution because fail if there’s null character in sbuf memcpy(&buff[4], sbuf.str().c_str(), streamsize);     textstreambuf.sputn(buff, streamsize + 4);     delete []buff;     return textstreambuf; }  int _tmain(int argc, _tchar* argv[]) {     std::stringbuf  stringbuffer, finalstringbuffer;     stringbuffer.sputn("this string testing", 33);     finalstringbuffer = createstreamwithheader(stringbuffer);      return 0; }

you can, , should, without ever prepending:

  1. record streambuf position
  2. seek forward or write placeholder of correct size
  3. write other data.
  4. seek beginning.
  5. overwrite placeholder final value.

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