Strict-aliasing and old-style-cast problem with C to C++ code

Hi,

I have some c code that I have put into my qt5 program but I get a lot of old-style-cast warnings which I would like to get rid of but don't quite know how to. I have tried reinterpret_cast but either I'm doing it incorrectly or it is not the right thing to do as it still results in the same error... :(

Thanks in advance!

Code:

warning: use of old-style cast [-Wold-style-cast]                      
warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]

Example code:

Code:

unsigned int j,k;
  unsigned int* jj;
  char* cptr;
  char buff[50];
 
      jj = (unsigned int*)&tmpY;  //recast as int as expected in htonl
      j = htonl(*jj);      //convert to network format
      cptr = (char*)&j;    //recast as a char * so can use indexing
      sprintf(buff,"Y=%7.2f ",tmpY);
      tmp=buff;
      s.append(buff);
      for(i=0;i<YLen;i++)
      {
        msg[YIndex+i] = cptr[i];
      }