Re: Temporary Object

Haochen Xie <>
Tue, 14 May 2013 22:01:20 -0700
Ian Collins wrote:

It's invalid because the standard says so!

In most cases, it makes little sense to perform non-const operations on
a temporary object.

Yeah, I also think that's the only reason why it's invalid, since you
could actually call a member function on a temporary object and the
function could pass itself as an argument to another function, which
could bypass this restriction (and that shows their should not be
technical difficulty).

Actually I saw this code from Crypto++ User's Guide by denis bider:

 // Crypto++
 #include "cryptlib.h"

 // std
 #include <iostream>

 void DumpMessage(CryptoPP::BufferedTransformation& bt)
     using namespace std;

     static char const* szHexDigits = "0123456789abcdef";
     byte b;
     while (bt.AnyRetrievable())
         if (!bt.Get(b))
             throw "Error: AnyRetrievable() returned true, "
                   "so this shouldn't happen.";

         // It is much easier to implement this using HexEncoder;
         // however, let's not get into that just yet. The below code
         // could do some special kind of processing that is not
         // supported by an off-the-shelf Filter class.

         cout << szHexDigits[(b >> 4) & 0x0f]
              << szHexDigits[b & 0x0f]
              << ' ';

 // Crypto++
 #include "filters.h"

 int main()
     using namespace CryptoPP;

     char const* szMessage = "How do you do?";
     DumpMessage(StringSource(szMessage, true));
         // If we constructed StringSource with 'false' instead
         // of 'true',
         // StringSource wouldn't call its PumpAll() method on
         // construction,
         // and no data would be extractable from the StringSource
         // object
         // until someone called the object's Pump() or PumpAll()
         // method.

     return 0;

That doesn't compile on my compiler, but it's on the tutorial anyway.
Probably the author's compiler does not follow the standard on this issue.

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