Topic 22: The C++ Standard Library

Synopsis

• Reinventing the wheel
   
• The "wheels" of C++
   
• The Standard Library^¤ - A box of wheels
   
• The string class^¤
   
• String example:
   
• The sequence container class^¤¤ templates
   
• Deque example
   
• The associative container classes^¤¤
   
• Map example
   
• The iostream classes^¤
   
• The complex class^¤ template
   
• Complex example
   
• Iterators^¤
   
• Iterator example 1
   
• Iterator example 2
   
• Other components
   
• Reading

Reinventing the wheel

• Try not to...
   
• ...it's boring
   
• ...it's expensive
   
• ...it's suprisingly difficult
   
• ...it's unnecessary

The "wheels" of C++

• I/O
   
• Character string manipulation
   
• Collections of objects (e.g. lists)
   
• Mathematical types and algorithms (complex, min/max, permutations)
   
• Other algorithms (sort, search, etc.)
   
• Support for Internationalization

The Standard Library^¤ - A box of wheels

• Pre-defined classes^¤ that provide useful components
   
• Part of the language standard so guaranteed to be available everywhere (i.e. portable)
   
• Written by experts (efficient, reliable)
   
• Makes code more maintainable
   
• Previously known as the STL or Standard Template Library^¤

The string class^¤

• Encapsulates a char* and the associated string-handling functionality
   
• Conversion to and from char*
   
• Concatenation, append, insert, replace, substring extraction
   
• Copy constructor^¤¤
   
• I/O
   
• Length and capacity
   
• Comparison
   
• Assignment
   
• Access to individual chars
   
• Search for substrings

String example:

#include <string>

using namespace std;
// AND LATER...

string s0;
string s1 = "cat";
string s2 = "alogue";

cout << s1 << s2 << endl;

s0 = s1 + s2;

int at = s0.find("log");

cout << s0.substr(at,3,5) << endl;

s1.replace(2,1,"nary");

char c = s2[4];

s2[4] = 'q';

The sequence container class^¤¤ templates

• Variations on a linear sequence of values
   
• Templated on the type of element they store
   
• Insertion and deletion
   
• Random access (but not to all container types)
   
• Pushing and popping to either end
   
• class vector (general purpose sequence class^¤)
   
• class deque (optimized for pushing/popping at either end)
   
• class list (optimized for sequential access and inserting in the middle; no random access)

Deque example

#include <deque>
using namespace std;

// AND LATER...

deque<string> names;

names.push_back("Shiranthi");
names.push_back("James");
names.push_back("Emily");
names.push_back("Damian");

names[2] = "Jesse";

for (int i=0; i<names.size(); i++)
{
	cout << names.at(i) << endl; // will throw exception if no element at i
}

//  or a better way to print elements
copy( names.begin(); names.end(); ostream_iterator<string>(cout,"\n")); // prints all elements separated by newlines

The associative container classes^¤¤

• A sequence which allows us to use keys other than integers
   
• map (give it a key, get/set a value)
   
• multimap (a map supporting multiple values per key)

Map example

#include <map>
using namespace std;

// AND LATER

map<string,int>       mark_for;

mark_for["Damian"] = 100;
while (markfile >> name >> mark)
{
	mark_for[name] = mark;
}
while (cin >> name)
{
	cout << name << " scored " << mark_for[name] << endl;
}

The iostream classes^¤

• istream/ostream for terminal I/O
   
• ifstream/ofstream for file I/O
   
• istringstream/ostringstream for I/O ops into/out of strings
   
• Will cover next lecture

The complex class^¤ template

• Implements complex numbers where each component is of some specified type
   
• Possible component types are float, double, long double
   
• Implements all arithmetic ops and functions on complex numbers

Complex example

#include <complex>
using namespace std;

// AND LATER....

complex<double> minus1 (-1,0);
complex<double> i      (0,1);
complex<double> pi     (3.141592654,0);

complex<double> sqrtminus1 = sqrt(minus1);

if (i !=  sqrtminus1)
{
	cout << "Warning: local anomoly in spacetime!" << endl;
	cout << "Checking fundamental constants:" << endl;
	cout << exp(pi*i)-1 << " (should be 0)" << endl;
}

Iterators^¤

• Act like pointers which can only step through a container.
   
• Most containers allow you to step through values by returning an iterator, which you then use
   
• "Find" operations on a container usually return an iterator, which steps through all matching values
   
• Many generic^¤ algorithms provided which make use of iterators^¤

Iterator example 1

#include <deque>
using namespace std;

// AND LATER...

deque<string> names;

names.push_back("Shiranthi");
names.push_back("James");
names.push_back("Emily");
names.push_back("Damian");

names[2] = "Jesse";

deque<string>::iterator next = names.begin();
deque<string>::iterator last = names.end();

for (; next != last; next++)
{
	cout << next->length() << endl;
}

Iterator example 2

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

// AND LATER...

vector<double> heights = load_heights();

// TALL HEIGHTS

for (vector<double>::iterator next = heights.begin();
     next != heights.end();
     next++)
{
	if (*next > 2.00)
	{
		cout << (*next) << endl;
	}
}

// SHORTEST 10 HEIGHTS

sort(heights.begin(),heights.end());

vector<double>::iterator from = heights.begin();
vector<double>::iterator to = from+10;

for(;from != to && from != heights.end(); from++)
{
	cout << (*from) << endl;
}

Other components

• Algorithms
   
• Localization
   
• Diagnostics and language support
   
• Standard exceptions^¤
   
• Standard C components

Reading

• Stroustrup: Chapters 16 to 22
   
• Lippman & Lajoie: Chapters 6 and 12
   
• Josuttis, N. M. The C++ Standard Library: A Tutorial and Reference, Addison-Wesley 1999.