+= and conversions

+= and conversions

• _gcvt

  Thanks for the link; I'm sorry for asking a question that was answered so recently. I had trouble finding any information about this as search engines respond very badly to things as '+='.
  
  The only thing I'm really concerned about is the speed of the code. I was under the impression x += y could be faster than x = x + y, in cases where 'x' has to be evaluated such as array[a * 2 + b] += y. Manually creating a temporary variable would be a bit ugly, and evaluating x twice is not an option obviously. On the other hand conversions are also slow. Perhaps I'd better overload these operators and do some speed tests.
  
  
  

• Michael McGranahan

  Hi,
  
  I'd better overload these operators and do some speed tests.
  
  I hope you will get a good result.
  
   
  
  
  

• Tatakau

  I need to add a bit of more info.
  
  Set " Treat Warning As Error" switch ON when you build it.
  
  
  

• Tran Van Thang

  Hi Astral,
  
  Just for your reference;
  
  #include <iostream>
  using namespace std;
  
  int main()
  {
      short a = 4;
      short b = 2;
     
      // b += a;
      short int c = short int (a + b);
      cout << c << endl;
  }
  
  Dr.Stroustrup repeats at varous places that "Type" is very important in C++. I always follow his advice. If someone else has a different opinio, plz let us know it.
  
  
  
  
  

• nbl

  Check this: http://forums.microsoft.com/MSDN/ShowPost.aspx PostID=171059&SiteID=1

  
  
  

• bgronek

  Hi,
  
  Thank you very much for the info. It's really interesting. I wil keep every logic as simple as possible so that the compiler understands my intention.
  
  Best,
  
  
  

• VinnieThaMadeMan

  I copied your code and did not get the error. Maybe you changed a setting somewhere.

  I mean I did not get a warning.

  
  

• pfdeveloper

  Takashi, I've compiled your code with Treat Warning as Error" and it compiles and runs (if I uncomment 'b += a;', it gives the warning/error again, of course). Here's the (expected) output:

  2
  2
  2
  2
  4
  4
  11

  The compiler also gives a warning for 'short int' (ie, 'sa += sb' will also result in a conversion).

  I forgot to mention, this warning is only there with warning set to Level 4. I created a default Win32 console project, and I don't remember changing much in VC's options (apart from some directories and such of course).

  
  

• Tim McDaniel

  Hi,
  
  Try this.
  
  #include <iostream>
  using namespace std;
  
  int main()
  {
      short a = 4;
      short b = 2;
      short int sa = 4;
      short int sb = 2;
      int c = 5;
      int d = 6;
      // b += a;
      c += d;
      cout << sizeof(a) << endl << sizeof(b) << endl;
      cout << sizeof(sa) << endl << sizeof(sb) << endl;
      cout << sizeof(c) << endl << sizeof(d) << endl;
      cout << c << endl;
  }
  
  Hope this helps.
  
  
  
• += and conversions