Английская Википедия:C++ Technical Report 1
Шаблон:Short description Шаблон:Multiple issues C++ Technical Report 1 (TR1) is the common name for ISO/IEC TR 19768, C++ Library Extensions, which is a document that proposed additions to the C++ standard library for the C++03 language standard. The additions include regular expressions, smart pointers, hash tables, and random number generators. TR1 was not a standard itself, but rather a draft document. However, most of its proposals became part of the later official standard, C++11. Before C++11 was standardized, vendors used this document as a guide to create extensions. The report's goal was "to build more widespread existing practice for an expanded C++ standard library".
The report was first circulated in draft form in 2005 as Draft Technical Report on C++ Library Extensions, then published in 2007 as an ISO/IEC standard as ISO/IEC TR 19768:2007.
Overview
Compilers did not need to include the TR1 components in order to conform to the C++ standard, because TR1 proposals were not part of the standard itself, only a set of possible additions that were still to be ratified. However, most of TR1 was available from Boost, and several compiler/library distributors implemented all or some of the components. TR1 is not the complete list of additions to the library that appeared in C++11. For example, C++11 includes a thread support library that is not available in TR1.
The new components were defined in the std::tr1
namespace to distinguish them from the then-current standard library.
Components
TR1 includes the following components:
General utilities
Reference wrapper – enables passing references, rather than copies, into algorithms or function objects. The feature was based on Boost.Ref.[1] A wrapper reference is obtained from an instance of the template class reference_wrapper
. Wrapper references are similar to normal references (‘&’) of the C++ language. To obtain a wrapper reference from any object the template class ref
is used (for a constant reference cref
is used).
Wrapper references are useful above all for template functions, when argument deduction would not deduce a reference (e.g. when forwarding arguments):
#include <iostream>
#include <tr1/functional>
void f( int &r ) { ++r; }
template< class Funct, class Arg >
void g( Funct f, Arg t )
{
f(t);
}
int main()
{
int i = 0;
g( f, i ); // 'g< void(int &r), int >' is instantiated
std::cout << i << "\n"; // Output: 0
g( f, std::tr1::ref(i) ); // 'g< void(int &r), reference_wrapper<int> >' is instanced
std::cout << i << "\n"; // Output: 1
}
Smart pointers – adds several classes that simplify object lifetime management in complex cases. Three main classes are added:
shared_ptr
– a reference-counted smart pointerweak_ptr
– a variant ofshared_ptr
that doesn't increase the reference count
The proposal is based on Boost Smart Pointer library.[2]
Function objects
These four modules are added to the <functional>
header file:
Polymorphic function wrapper (function
) – can store any callable function (function pointers, member function pointers, and function objects) that uses a specified function call signature. The type does not depend on the kind of the callable used. Based on Boost.Function[3]
Function object binders (bind
) – can bind any parameter parameters to function objects. Function composition is also allowed. This is a generalized version of the standard std::bind1st
and std::bind2nd
bind functions. The feature is based on Boost Bind library.[4]
Function return types (result_of
) – determines the type of a call expression.
Member functions (mem_fn
) – enhancement to the standard std::mem_fun
and std::mem_fun_ref
. Allows pointers to member functions to be treated as function objects. Based on Boost Mem Fn library.[5]
Metaprogramming and type traits
There is now <type_traits>
header file that contains many useful trait meta-templates, such as is_pod
, has_virtual_destructor
, remove_extent
, etc. It facilitates metaprogramming by enabling queries on and transformation between different types. The proposal is based on Boost Type Traits library.[6]
Numerical facilities
Random number generation
- new
<random>
header file –variate_generator
,mersenne_twister
,poisson_distribution
, etc. - utilities for generating random numbers using any of several Pseudorandom number generators, engines, and probability distributions
Mathematical special functions
Some features of TR1, such as the mathematical special functions and certain C99 additions, are not included in the Visual C++ implementation of TR1. The Mathematical special functions library was not standardized in C++11.
These functions will likely be of principal interest to programmers in the engineering and scientific disciplines.
The following table shows all 23 special functions described in TR1.
Function name | Function prototype | Mathematical expression |
---|---|---|
Associated Laguerre polynomials | double assoc_laguerre( unsigned n, unsigned m, double x ) ; | <math>{L_n}^m(x) = (-1)^m \frac{d^m}{dx^m} L_{n+m}(x), \text{ for } x \ge 0</math> |
Associated Legendre polynomials | double assoc_legendre( unsigned l, unsigned m, double x ) ; | <math>{P_l}^m(x) = (1-x^2)^{m/2} \frac{d^m}{dx^m} P_l(x), \text{ for } x \ge 0</math> |
Beta function | double beta( double x, double y ) ; | <math>\Beta(x,y)=\frac{\Gamma(x) \Gamma(y)}{\Gamma(x+y)}</math> |
Complete elliptic integral of the first kind | double comp_ellint_1( double k ) ; | <math>K(k) = F\left(k, \textstyle \frac{\pi}{2}\right) = \int_0^{\frac{\pi}{2}} \frac{d\theta}{\sqrt{1 - k^2 \sin^2 \theta}}</math> |
Complete elliptic integral of the second kind | double comp_ellint_2( double k ) ; | <math>E\left(k, \textstyle \frac{\pi}{2}\right) = \int_0^{\frac{\pi}{2}} \sqrt{1 - k^2 \sin^2 \theta}\; d\theta</math> |
Complete elliptic integral of the third kind | double comp_ellint_3( double k, double nu ) ; | <math>\Pi\left(\nu, k, \textstyle \frac{\pi}{2}\right) = \int_0^{\frac{\pi}{2}} \frac{d\theta}{(1 - \nu \sin^2 \theta)\sqrt{1 - k^2 \sin^2 \theta}}</math> |
Confluent hypergeometric functions | double conf_hyperg( double a, double c, double x ) ; | <math>F(a, c, x) = \frac{\Gamma(c)}{\Gamma(a)} \sum_{n = 0}^\infty \frac{\Gamma(a + n) x^n}{\Gamma(c + n) n!}</math> |
Regular modified cylindrical Bessel functions | double cyl_bessel_i( double nu, double x ) ; | <math>I_\nu(x) = i^{-\nu} J_\nu(ix) = \sum_{k = 0}^\infty \frac{(x/2)^{\nu + 2k}}{k! \; \Gamma(\nu + k + 1)}, \text{ for } x \ge 0</math> |
Cylindrical Bessel functions of the first kind | double cyl_bessel_j( double nu, double x ) ; | <math>J_\nu(x) = \sum_{k = 0}^\infty \frac{(-1)^k \; (x/2)^{\nu + 2k}}{k! \; \Gamma(\nu + k + 1)}, \text{ for } x \ge 0</math> |
Irregular modified cylindrical Bessel functions | double cyl_bessel_k( double nu, double x ) ; | <math>\begin{align}
K_\nu(x) & = \textstyle\frac{\pi}{2} i^{\nu+1} \big(J_\nu(ix) + i N_\nu(ix)\big) \\ & = \begin{cases} \displaystyle \frac{I_{-\nu}(x) - I_\nu(x)}{\sin \nu\pi}, & \text{for } x \ge 0 \text{ and } \nu \notin \mathbb{Z} \\[10pt] \displaystyle \frac{\pi}{2} \lim_{\mu \to \nu} \frac{I_{-\mu}(x) - I_\mu(x)}{\sin \mu\pi}, & \text{for } x < 0 \text{ and } \nu \in \mathbb{Z} \\ \end{cases} \end{align}</math> |
Cylindrical Neumann functions | double cyl_neumann( double nu, double x ) ; | <math>
N_\nu(x) = \begin{cases} \displaystyle \frac{J_\nu(x)\cos \nu\pi - J_{-\nu}(x)}{\sin \nu\pi}, & \text{for } x \ge 0 \text{ and } \nu \notin \mathbb{Z} \\[10pt] \displaystyle \lim_{\mu \to \nu} \frac{J_\mu(x)\cos \mu\pi - J_{-\mu}(x)}{\sin \mu\pi}, & \text{for } x < 0 \text{ and } \nu \in \mathbb{Z} \\ \end{cases} </math> |
Incomplete elliptic integral of the first kind | double ellint_1( double k, double phi ) ; | k\right| \le 1</math> |
Incomplete elliptic integral of the second kind | double ellint_2( double k, double phi ) ; | k\right| \le 1</math> |
Incomplete elliptic integral of the third kind | double ellint_3( double k, double nu, double phi ) ; | k\right| \le 1</math> |
Exponential integral | double expint( double x ) ; | <math> \mbox{E}i(x)=-\int_{-x}^{\infty} \frac{e^{-t}}{t}\, dt</math> |
Hermite polynomials | double hermite( unsigned n, double x ) ; | <math>H_n(x)=(-1)^n e^{x^2}\frac{d^n}{dx^n}e^{-x^2}\,\!</math> |
Hypergeometric series | double hyperg( double a, double b, double c, double x ) ; | <math>F(a,b,c,x)=\frac{\Gamma(c)}{\Gamma(a)\Gamma(b)}\sum_{n = 0}^\infty\frac{\Gamma(a+n)\Gamma(b+n)}{\Gamma(c+n)}\frac{x^n}{n!}</math> |
Laguerre polynomials | double laguerre( unsigned n, double x ) ; | <math>L_n(x)=\frac{e^x}{n!}\frac{d^n}{dx^n}\left(x^n e^{-x}\right), \text{ for } x \ge 0</math> |
Legendre polynomials | double legendre( unsigned l, double x ) ; | x\right| \le 1 </math> |
Riemann zeta function | double riemann_zeta( double x ) ; | <math>
\Zeta(x) = \begin{cases} \displaystyle \sum_{k = 1}^\infty k^{-x}, & \text{for } x > 1 \\[10pt] \displaystyle 2^x\pi^{x-1}\sin\left(\frac{x\pi}{2}\right)\Gamma(1-x)\zeta(1-x), & \text{for } x < 1 \\ \end{cases} </math> |
Spherical Bessel functions of the first kind | double sph_bessel( unsigned n, double x ) ; | <math>j_n(x) = \sqrt{\frac{\pi}{2x}} J_{n+1/2}(x), \text{ for } x \ge 0</math> |
Spherical associated Legendre functions | double sph_legendre( unsigned l, unsigned m, double theta ) ; | m| \leq l</math> |
Spherical Neumann functions | double sph_neumann( unsigned n, double x ) ; | <math>n_n(x) = \left(\frac{\pi}{2x}\right)^{\frac{1}{2}}N_{n+\frac{1}{2}}(x), \text{ for } x \ge 0</math> |
Each function has two additional variants. Appending the suffix ‘f’ or ‘l’ to a function name gives a function that operates on float
or long double
values respectively. For example:
float sph_neumannf( unsigned n, float x ) ;
long double sph_neumannl( unsigned n, long double x ) ;
Containers
Tuple types
- new
<tuple>
header file –tuple
- based on Boost Tuple library[7]
- vaguely an extension of the standard
std::pair
- fixed size collection of elements, which may be of different types
Fixed size array
- new
<array>
header file –array
- taken from Boost Array library[8]
- as opposed to dynamic array types such as the standard
std::vector
Hash tables
- new
<unordered_set>
,<unordered_map>
header files - they implement the
unordered_set
,unordered_multiset
,unordered_map
, andunordered_multimap
classes, analogous toset
,multiset
,map
, andmultimap
, respectively- unfortunately,
unordered_set
andunordered_multiset
cannot be used with theset_union
,set_intersection
,set_difference
,set_symmetric_difference
, andincludes
standard library functions, which work forset
andmultiset
- unfortunately,
- new implementation, not derived from an existing library, not fully API compatible with existing libraries
- like all hash tables, often provide constant time lookup of elements but the worst case can be linear in the size of the container
Regular expressions
- new
<regex>
header file –regex
,regex_match
,regex_search
,regex_replace
, etc. - based on Boost RegEx library[9]
- pattern matching library
C compatibility
C++ is designed to be compatible with the C programming language, but is not a strict superset of C due to diverging standards. TR1 attempts to reconcile some of these differences through additions to various headers in the C++ library, such as <complex>, <locale>, <cmath>, etc. These changes help to bring C++ more in line with the C99 version of the C standard (not all parts of C99 are included in TR1).
Technical Report 2
In 2005, a request for proposals for a TR2 was made with a special interest in Unicode, XML/HTML, Networking and usability for novice programmers.TR2 call for proposals.
Some of the proposals included:
- Threads [1]
- The Asio C++ library (networking [2][3]).
- Signals/Slots [sigc Proposal for standardization in C++ Library TR2][4]
- Filesystem Library Filesystem Library for TR2 – Based on the Boost Filesystem Library, for query/manipulation of paths, files and directories.
- Boost Any Library Any Library Proposal for TR2
- Lexical Conversion Library Conversion Library Proposal for TR2
- New String Algorithms Proposal for new string algorithms in TR2
- Toward a More Complete Taxonomy of Algebraic Properties for Numeric Libraries in TR2 ISO/IEC JTC1/SC22/WG21 - Papers 2008
- Adding heterogeneous comparison lookup to associative containers for TR2 [5]
After the call was issued for proposals for TR2, ISO procedures were changed, so there will not be a TR2. Instead, enhancements to C++ will be published in a number of Technical Specifications. Some of the proposals listed above are already included in the C++ standard or in draft versions of the Technical Specifications.
See also
- C++11, standard for the C++ programming language; the library improvements were based on TR1
- C11 (C standard revision), a revision of the C standard which incorporated some features proposed in TR1
- Boost library, a large collection of portable C++ libraries, several of which were included in TR1
- Standard Template Library, part of the current C++ Standard Library
References
Sources
External links
- Scott Meyers' Effective C++: TR1 Information – contains links to the TR1 proposal documents which provide background and rationale for the TR1 libraries.