The C++ Standard Library

C++ remains a very popular language. Its standard library is definitely worth mastering.


Goals and Objectives

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

What this page is about

What this page is not about

Some Introductory Examples

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


The standard library was created many years after C++ itself.

Standard Library Design

Structure of the Library

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

<algorithm>, <bitset>, <cassert>, <cctype>, <cerrno>, <cfloat>, <ciso646>, <climits>, <clocale>, <cmath>, <complex>, <csetjmp>, <csignal>, <cstdarg>, <cstddef>, <cstdio>, <cstdlib>, <cstring>, <ctime>, <cwchar>, <cwctype>, <deque>, <exception>, <fstream>, <functional>, <iomanip>, <ios>, <iosfwd>, <iostream>, <istream>, <iterator>, <limits>, <list>, <locale>, <map>, <memory>, <new>, <numeric>, <ostream>, <queue>, <set>, <sstream>, <stack>, <stdexcept>, <streambuf>, <string>, <typeinfo>, <utility>, <valarray>, <vector>

Logical Organization

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

Tour of the Library


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

<vector> one-dimensional arrays
<list> doubly-linked lists
<deque> double-ended queues
<queue> FIFO queues and priority queues
<stack> stacks
<map> dictionaries (associative arrays)
<set> sets
<bitset> bit sequences

List Example

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

int main(int, char**) {
  list<string> names;	// default constructor makes it empty
  for (list<string>::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<string, int>::iterator i =  m.find("juan");
  if (i != m.end()) {
    cout << (*i).second << '\n' << m.size() << '\n';

Container Interface

Utilities, Iterators and Algorithms

<utility> operators and pairs
<functional> function objects
<memory> allocators for containers
<iterator> iterators
<algorithm> general 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<int>());
  for (int i = 0; i < a.size(); i++) cout << a[i] << ' ';


<stdexcept> defines some standard exception classes thrown by many library operations
<cassert> contains the assert() macro
<cerrno> C-style error handling, needed to support legacy code


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';


<ios> basic stream types and ops
<streambuf> buffers for streams
<istream> input stream template class
<ostream> output stream template class
<iostream> standard streams like cin and cout
<fstream> files to/from streams
<sstream> strings to/from streams
<iomanip> some stream manipulators

Stream Example

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

int main(int, char**) {
  ifstream f;
  double x;"numbers.txt");
  if (!f) throw new runtime_error("missing file");
  while (true) {
    f >> x;
    if (f.bad()) throw new runtime_error("corrupted");
    if ( {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


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

<limits> numeric limits
<new> dynamic memory management
<typeinfo> RTTI support
<exception> exception class

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


<complex> a class for complex numbers

and many global operations

<valarray> numeric vectors and operations
<numeric> generalized numeric operations: accumulate(), partial_sum(), adjacent_difference(), inner_product()
<cmath> mathematical functions
<cstdlib> C-style random numbers and abs(), fabs(), div()

Concluding Remarks