Chapter 4.  Support

Table of Contents

Fundamental Types
Numeric Properties
Dynamic Memory
Termination Handlers
Verbose Terminate Handler

This part deals with the functions called and objects created automatically during the course of a program's existence.

While we can't reproduce the contents of the Standard here (you need to get your own copy from your nation's member body; see our homepage for help), we can mention a couple of changes in what kind of support a C++ program gets from the Standard Library.


Fundamental Types

C++ has the following builtin types:

  • char

  • signed char

  • unsigned char

  • signed short

  • signed int

  • signed long

  • unsigned short

  • unsigned int

  • unsigned long

  • bool

  • wchar_t

  • float

  • double

  • long double

These fundamental types are always available, without having to include a header file. These types are exactly the same in either C++ or in C.

Specializing parts of the library on these types is prohibited: instead, use a POD.

Numeric Properties

The header limits defines traits classes to give access to various implementation defined-aspects of the fundamental types. The traits classes -- fourteen in total -- are all specializations of the template class numeric_limits, documented here and defined as follows:

   template<typename T>
     struct class
       static const bool is_specialized;
       static T max() throw();
       static T min() throw();

       static const int digits;
       static const int digits10;
       static const bool is_signed;
       static const bool is_integer;
       static const bool is_exact;
       static const int radix;
       static T epsilon() throw();
       static T round_error() throw();

       static const int min_exponent;
       static const int min_exponent10;
       static const int max_exponent;
       static const int max_exponent10;

       static const bool has_infinity;
       static const bool has_quiet_NaN;
       static const bool has_signaling_NaN;
       static const float_denorm_style has_denorm;
       static const bool has_denorm_loss;
       static T infinity() throw();
       static T quiet_NaN() throw();
       static T denorm_min() throw();

       static const bool is_iec559;
       static const bool is_bounded;
       static const bool is_modulo;

       static const bool traps;
       static const bool tinyness_before;
       static const float_round_style round_style;


The only change that might affect people is the type of NULL: while it is required to be a macro, the definition of that macro is not allowed to be (void*)0, which is often used in C.

For g++, NULL is #define'd to be __null, a magic keyword extension of g++.

The biggest problem of #defining NULL to be something like 0L is that the compiler will view that as a long integer before it views it as a pointer, so overloading won't do what you expect. (This is why g++ has a magic extension, so that NULL is always a pointer.)

In his book Effective C++, Scott Meyers points out that the best way to solve this problem is to not overload on pointer-vs-integer types to begin with. He also offers a way to make your own magic NULL that will match pointers before it matches integers.

See the Effective C++ CD example.