The C++ Standard Library

Outline

• Background
• What is in the Standard Library
• Organization of the Library
• Tour of the Library
• Overview of the Modules
• Code Examples
• Concluding Remarks

Goals and Objectives

To present the overall organization and examples of the use of the C++ Standard Library so that:

• Programmers will be able to start using the library right away.
• Programmers will be able to get rid of tons of poorly commented, under-tested, non-standard, container libraries that defy (large-scale) reuse

What this page is about

• What is in the Standard Library and how the library is organized
• Why the Standard Library looks the way it does
• How to write code using the Standard Library (via examples)
• Helping you to become a better C++ programmer

What this page is not about

• Introductory C++ Programming
• Object Oriented Programming (the library purposely has a very evident non-object-oriented feel!)
• Detailed contents of the headers (we prefer code samples)
• Language Wars
• Alexander Stepanov

C + +

ISO C++?

C++ is a standard. However the language was first used in the mid 1980s and evolved rapidly before being standardized in 1998. Many existing compilers have not caught up to the standard, and have so many vendor-specific "enhancements" it's difficult to write good standard code. In fact many compilers still support language features that have been removed from the language.

Evolution of C++

There have been many language changes since 1990 that many people are not aware of, such as templates, exceptions, bool, true, false, explicit, new-style casts, The Standard Library, namespaces, RTTI, member templates, typename, declarations in if and while conditions, explicit instantiation, new keywords, ...

Simple Example 1

#include <iostream>
#include <string>

int main(int argc, char** argv) {
  std::string name;
  if (argc > 1) name = argv[1];
  else std::cin >> name;
  std::cout << "Hello, " + name;
  return 0;
}

Simple Example 2

#include <iostream>
#include <string>
using namespace std;

int main(int argc, char** argv) {
  string name;
  if (argc > 1) name = argv[1];
  else cin >> name;
  cout << "Hello, " + name;
  return 0;
}

Library Overview

Motivation

• C++ is too popular to not have a standard library
• Everyone, it seems, has written wrappers for everything (witness too many incompatible and buggy string classes)
• The Standard C++ Library should contain the Standard C Library as a subset

Standard Library Design

• Provides support for language features (e.g. RTTI, memory management)
• Supplies implementation-dependent information (like limits)
• Supplies functions that you wouldn't write in C++ itself so they can be optimized for a particular platform (e.g., sqrt, memmove)
• Supplies non-primitive facilities to encourage portability (e.g. containers, sort functions, I/O streams)
• Has conventions for extending the facilities it does provide
• Is not stuffed with non-universal facilities such as graphics and pattern matching

Structure of the Library

The Standard Library is comprised of 50 modules (18 are from C):

Logical Organization

It is useful to group the 50 modules into ten informal categories:

• Containers
• General Utilities
• Iterators
• Algorithms
• Diagnostics
• Strings
• Input / Output
• Localization
• Language Support
• Numerics

Tour of the Library

Containers

• The Standard Library's container classes use templates (genericity) and not inheritance! (No abstract base container class: containers simply support a standard, recognizable set of basic operations)
• Design is "the result of a single-minded search for uncompromisingly efficient and generic algorithms"

The containers in the standard library are found in these modules:

List Example

#include <iostream>
#include <list>
#include <string>
using namespace std;

int main(int, char**) {
  list<string> names;	// default constructor makes it empty
  names.push_back("dva");
  names.push_front("odin");
  names.push_back("tri");
  for (list::iterator i = names.begin(); i != names.end(); i++) {
    cout << *i << '\n';
  }
  return 0;
}

Map Example

#include <iostream>
#include <map>
#include <string>
using namespace std;

int main(int, char**) {
  map<string, int> m;
  m["juan"] = 19;
  m["svetlana"] = 26;
  cout << m["ciaran"] << '\n';
  map::iterator i =  m.find("juan");
  if (i != m.end()) {
    cout << (*i).second << '\n' << m.size() << '\n';
  }
}

Container Interface

• Standard Containers are all template classes which contain
• typedefs iterator, reverse_iterator, and others
• empty(), clear(), erase(), size(), max_size(), begin(), end(), rbegin(), rend(), swap(), and get_allocator()
• Certain containers have other members
• There is no hierarchy of containers!

Utilities, Iterators and Algorithms

The header <cstdlib> contains bsearch() and qsort() which are underpowered, useless and inefficient.

Some Algorithms

<algorithm> contains, among others, for_each(), find(), find_if(), count(), count_if(), search(), equal(), copy(), swap(), replace(), fill(), remove(), remove_if(), unique(), reverse(), random_shuffle(), sort(), merge(), partition(), binary_search(), includes(), set_union(), make_heap(), min(), max(), next_permutation()

Algorithm Example

#include <iostream>
#include <algorithm>
#include <functional>
#include <vector>
using namespace std;

int main(int, char**) {
  vector<int> a;  for (int i = 0; i < 100; i++) a.push_back(i);
  random_shuffle(a.begin(), a.begin()+75);
  for (int i = 0; i < a.size(); i++) cout << a[i] << ' ';
  sort(a.begin(), a.end(), greater());
  for (int i = 0; i < a.size(); i++) cout << a[i] << ' ';
}

Diagnostics

Strings

• The header <string> defines the template class basic_string and the classes string and wstring, which are instantiations of basic_string with char and wchar.
• Strings have real copy semantics, you can assign using =, compare with <= and >, etc.
• Prefer strings to error-prone C-style char pointers

String Example

#include <iostream>
#include <string>
using namespace std;

int main(int, char**) {
  string s1 = "Hello", s2("Goodbye"), s3, s4(s2, 4,3);
  s3 = s1; s3[1] = 'u';
  cout << s1 << ' ' << s3 << s2.length() << '\n';
  string message = s1 + ',' + " then " + s2;
  message.replace(7, 4, "and");
  cout << message << s4 << ' ' << s2.find('y') << '\n';
}

Input/Output

Stream Example

#include <iostream>
#include <iomanip>
#include <fstream>
#include <stdexcept>
using namespace std;

int main(int, char**) {
  ifstream f;
  double x;
  f.open("numbers.txt");
  if (!f) throw new runtime_error("missing file");
  while (true) {
    f >> x;
    if (f.bad()) throw new runtime_error("corrupted");
    if (f.fail()) {if (f.eof()) break; else throw new runtime_error("junk");}
    cout << fixed << setprecision(4) << x << '\n';
  } // note stream f closed in destructor
} // note catching and reporting runtime_errors omitted for space

Localization

The header <locale> contains a class called locale, other classes such as money_get and money_put, and a number of operations such as isalpha(), isdigit(), isalnum(), isspace(), ispunct(), iscntrl(), isupper(), islower(), toupper(), tolower()

Language Support

In addition there are several headers from the C library: <climits>, <cfloat>, <cstddef>, <cstdarg>, <csetjmp>, <cstdlib>, <ctime>, <csignal>

Numerics

and many global operations

Concluding Remarks

Advice

• Use the Standard Library in all your new work; port old code to practice if feasible
• Remember the "C-style" way is almost always inferior to the "C++-style"
• Compose your own quick-reference guide to library facilities
• Read the Advice sections (16.4, 17.7, 18.12, 19.5, 20.5, 21.10, 22.8) in Stroustrup's book