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Support
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Standard Contents
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Support
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< a id = "idm269893583920" class = "indexterm" > < / a >
< / h2 > < / div > < / div > < / div > < div class = "toc" > < p > < strong > Table of Contents< / strong > < / p > < dl class = "toc" > < dt > < span class = "section" > < a href = "support.html#std.support.types" > Types< / a > < / span > < / dt > < dd > < dl > < dt > < span class = "section" > < a href = "support.html#std.support.types.fundamental" > Fundamental Types< / a > < / span > < / dt > < dt > < span class = "section" > < a href = "support.html#std.support.types.numeric_limits" > Numeric Properties< / a > < / span > < / dt > < dt > < span class = "section" > < a href = "support.html#std.support.types.null" > NULL< / a > < / span > < / dt > < / dl > < / dd > < dt > < span class = "section" > < a href = "dynamic_memory.html" > Dynamic Memory< / a > < / span > < / dt > < dt > < span class = "section" > < a href = "termination.html" > Termination< / a > < / span > < / dt > < dd > < dl > < dt > < span class = "section" > < a href = "termination.html#support.termination.handlers" > Termination Handlers< / a > < / span > < / dt > < dt > < span class = "section" > < a href = "termination.html#support.termination.verbose" > Verbose Terminate Handler< / a > < / span > < / dt > < / dl > < / dd > < / dl > < / div > < p >
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This part deals with the functions called and objects created
automatically during the course of a program's existence.
< / p > < p >
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.
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< / p > < div class = "section" > < div class = "titlepage" > < div > < div > < h2 class = "title" style = "clear: both" > < a id = "std.support.types" > < / a > Types< / h2 > < / div > < / div > < / div > < div class = "section" > < div class = "titlepage" > < div > < div > < h3 class = "title" > < a id = "std.support.types.fundamental" > < / a > Fundamental Types< / h3 > < / div > < / div > < / div > < p >
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C++ has the following builtin types:
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< / p > < div class = "itemizedlist" > < ul class = "itemizedlist" style = "list-style-type: disc; " > < li class = "listitem" > < p >
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char
< / p > < / li > < li class = "listitem" > < p >
signed char
< / p > < / li > < li class = "listitem" > < p >
unsigned char
< / p > < / li > < li class = "listitem" > < p >
signed short
< / p > < / li > < li class = "listitem" > < p >
signed int
< / p > < / li > < li class = "listitem" > < p >
signed long
< / p > < / li > < li class = "listitem" > < p >
unsigned short
< / p > < / li > < li class = "listitem" > < p >
unsigned int
< / p > < / li > < li class = "listitem" > < p >
unsigned long
< / p > < / li > < li class = "listitem" > < p >
bool
< / p > < / li > < li class = "listitem" > < p >
wchar_t
< / p > < / li > < li class = "listitem" > < p >
float
< / p > < / li > < li class = "listitem" > < p >
double
< / p > < / li > < li class = "listitem" > < p >
long double
< / p > < / li > < / ul > < / div > < p >
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.
< / p > < p >
Specializing parts of the library on these types is prohibited:
instead, use a POD.
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< / p > < / div > < div class = "section" > < div class = "titlepage" > < div > < div > < h3 class = "title" > < a id = "std.support.types.numeric_limits" > < / a > Numeric Properties< / h3 > < / div > < / div > < / div > < p >
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The header < code class = "filename" > limits< / code > 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
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< code class = "classname" > numeric_limits< / code > , documented < a class = "link" href = "http://gcc.gnu.org/onlinedocs/libstdc++/latest-doxygen/a00593.html" target = "_top" > here< / a >
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and defined as follows:
< / p > < pre class = "programlisting" >
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;
};
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< / pre > < / div > < div class = "section" > < div class = "titlepage" > < div > < div > < h3 class = "title" > < a id = "std.support.types.null" > < / a > NULL< / h3 > < / div > < / div > < / div > < p >
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The only change that might affect people is the type of
< code class = "constant" > NULL< / code > : while it is required to be a macro,
the definition of that macro is < span class = "emphasis" > < em > not< / em > < / span > allowed
to be < code class = "constant" > (void*)0< / code > , which is often used in C.
< / p > < p >
For < span class = "command" > < strong > g++< / strong > < / span > , < code class = "constant" > NULL< / code > is
< code class = "code" > #define< / code > 'd to be
< code class = "constant" > __null< / code > , a magic keyword extension of
< span class = "command" > < strong > g++< / strong > < / span > .
< / p > < p >
The biggest problem of #defining < code class = "constant" > NULL< / code > to be
something like < span class = "quote" > “< span class = "quote" > 0L< / span > ”< / span > 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
< span class = "command" > < strong > g++< / strong > < / span > has a magic extension, so that
< code class = "constant" > NULL< / code > is always a pointer.)
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< / p > < p > In his book < a class = "link" href = "http://www.aristeia.com/books.html" target = "_top" > < span class = "emphasis" > < em > Effective
C++< / em > < / span > < / a > , Scott Meyers points out that the best way
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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
< code class = "constant" > NULL< / code > that will match pointers before it
matches integers.
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< / p > < p > See the
< a class = "link" href = "http://www.aristeia.com/books.html" target = "_top" > < span class = "emphasis" > < em > Effective
C++ CD< / em > < / span > < / a > example.
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