What breaking changes are introduced in C++11?

Question

I know that at least one of the changes in C++11 that will cause some old code to stop compiling: the introduction of explicit operator bool() in the standard l

Answer 1

Stream extraction failure is treated differently.

Example

#include 
#include 

int main()
{
   std::stringstream ss;
   ss << '!';
   
   int x = -1;
   
   assert(!(ss >> x)); // C++03 and C++11
   assert(x == -1);    // C++03
   assert(x == 0);     // C++11
}

Change proposal

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3246.html#23

Standard reference

[C++03: 22.2.2.1.2/11]: The result of stage 2 processing can be one of

• A sequence of chars has been accumulated in stage 2 that is converted (according to the rules of scanf) to a value of the type of val. This value is stored in val and ios_base::goodbit is stored in err.
• The sequence of chars accumulated in stage 2 would have caused scanf to report an input failure. ios_base::failbit is assigned to err. [ed: Nothing is stored in val.]

[C++11: 22.4.2.1.2/3]: [..] The numeric value to be stored can be one of:

• zero, if the conversion function fails to convert the entire field. ios_base::failbit is assigned to err.
• the most positive representable value, if the field represents a value too large positive to be represented in val. ios_base::failbit is assigned to err.
• the most negative representable value or zero for an unsigned integer type, if the field represents a value too large negative to be represented in val. ios_base::failbit is assigned to err.
• the converted value, otherwise.

The resultant numeric value is stored in val.

Implementations

• GCC 4.8 correctly outputs for C++11:

  Assertion `x == -1' failed

• GCC 4.5-4.8 all output for C++03 the following, which would appear to be a bug:

  Assertion `x == -1' failed

• Visual C++ 2008 Express correctly outputs for C++03:

  Assertion failed: x == 0

• Visual C++ 2012 Express incorrectly outputs for C++11, which would appear to be a status-of-implementation issue:

  Assertion failed: x == 0