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STL is a conventional name of the C++ Standard Library.
The abbreviation STL originated in 1994 and stands for Standard Template Library
STL includes:
C Standard Library
String support
Stream I/O support for files and devices
Numerical computation support:
Complex numbers
Vectors with arithmetic operators
Support for Containers (data structures) and algorithms (functions)
Major STL components are
Containers are objects such as vector, list, map
Iterators are objects behaving like pointers that define ranges inside containers
Algorithms are fundamental data manipulation tasks: sort, count, copy, reverse, etc.
Containers and iterators are C++ objects
Algorithms are C++ functions
STL facilities work correctly with any data type, because they are template -based.
An animation of STL components helps to visualize how STL components interact at runtime.
Using prefabricated templates from the STL library is easy:
#include <vector>
#include <string>
using namespace std;
int main (int argc, char* argv[])
{
vector< double > vd; // vd elements are floating point numbers
vector< int > vi; // vi elements are integer numbers
vector< string > vs; // vs elements are string objects
return 0;
}
The typenames which appear inside angled brackets are template parameters.
Template function calls normally ommit template parameters,
because the typenames can be absorbed directly from the actual function call parameters.
However, template parameters of functions may also be specified by the programmer:
#include <cassert>
#include <algorithm>
using namespace std;
int main (int argc, char* argv[])
{
int one = 1;
int two = 2;
swap< int >( one, two ); // explicit template param
swap( one, two ); // implicit template param
assert( one == 1 );
assert( two == 2 );
return 0;
}
Because swap expects both arguments to be of the same type, it needs only one template parameter.
STL containers replicate behavior of data structures commonly used in programming:
dynamic string
dynamic array: vector
heap: priority_queue
linked list
tree: set
associative array: map
A stack is a container that permits to insert and extract its elements only from the top of the container:
#include <cassert>
#include <stack>
using namespace std;
int main (int argc, char* argv[])
{
stack< int > st;
st.push( 100 ); // push number on the stack
assert( st.size() == 1 ); // verify one element is on the stack
assert( st.top() == 100 );// verify element value
st.top() = 456; // assign new value
assert( st.top() == 456 );
st.pop(); // remove element
assert( st.empty() == true );
return 0;
}
A set is a container that holds unique elements.
The elements in std::set are always sorted.
#include <cassert>
#include <iostream>
#include <set>
using namespace std;
int main (int argc, char* argv[])
{
set< int > iset; // set of unique integer numbers
iset.insert( 11 ); // populate set with some values
iset.insert( -11 );
iset.insert( 55 );
iset.insert( 22 );
iset.insert( 22 );
if ( iset.find( 55 ) != iset.end() ) { // is value already stored?
iset.insert( 55 );
}
assert( iset.size() == 4 ); // sanity check :-)
set< int >::iterator it;
for ( it = iset.begin(); it != iset.end(); it++ ) {
cout << " " << *it;
}
return 0;
}
// Output: -11 11 22 55
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Functions that need to return two values often return a pair:
pair< bool, double > result = do_a_calculation();
if ( result.first ) {
do_something_more( result.second );
} else {
report_error();
}
An iterator is an object that provides access to objects stored in STL containers.
Iterators are designed to behave like C++ pointers.
#include <iostream>
#include <vector>
using namespace std;
int main (int argc, char* argv[])
{
vector< int > vint( 3 ); // vector with 3 integer numbers
vint[ 0 ] = 10;
vint[ 1 ] = 20;
vint[ 2 ] = 30;
// Display elements of the vector:
vector< int >::iterator it;
for ( it = vint.begin(); it != vint.end(); ++it ) {
// Like pointer, iterator is dereferenced to
// access the value of the element pointed by it:
cout << " " << *it;
}
return 0;
}
// Output: 10 20 30
// Using iterator after content of the container changes:
vect.insert( data );
++iter; // Can be DANGEROUS! Iterator may be invalid!
// Navigating and dereferencing the iterator to access the data:
++iter;
*iter = data;
cout << *iter;
iter = data; // incorrect
cout << iter; // incorrect
A map is a container that holds unique pairs of keys and values.
The elements in std::map are always sorted by its keys.
Each element of the map is formed by the combination of the key value and a mapped value.
Map iterators access both the key and the mapped value at the same time.
#include <cassert>
#include <iostream>
#include <string>
#include <map>
using namespace std;
int main (int argc, char* argv[])
{
map< string, string > phone_book;
phone_book[ "411" ] = "Directory";
phone_book[ "911" ] = "Emergency";
phone_book[ "508-678-2811" ] = "BCC";
if ( phone_book.find( "411" ) != phone_book.end() ) {
phone_book.insert(
make_pair(
string( "411" ),
string( "Directory" )
)
);
}
assert( phone_book.size() == 3 );
map< string, string >::iterator it;
for ( it = phone_book.begin(); it != phone_book.end(); ++it ) {
cout
<< " " << it->first
<< " " << it->second
<< endl
;
}
return 0;
}
/* Output:
411 Directory
508-678-2811 BCC
911 Emergency
*/
A string is an STL container designed to accommodate sequence of characters, that is, text.
Strings provide built-in features to operate on fragments of text and individual characters.
The design is more intuitive than zero-terminated character arrays, commonly known as C-strings.
#include <cassert>
#include <string>
using namespace std;
int main (int argc, char* argv[])
{
string str( "Hello" );
for ( int idx = 0; idx < str.length(); ++idx ) {
// Access and modify individual characters:
str[ idx ] = toupper( str[ idx ] );
}
assert( str == "HELLO" );
str.append( 3, '!' ); // add three exclamation points
assert( str == "HELLO!!!" );
int pos1 = str.find( "L" ); // HELLO!!!
int pos2 = str.rfind( "L" ); // ||
assert( pos1 == 2 ); // pos1-''-pos2
assert( pos2 == 3 );
// Get 2-character long substring starting at pos1:
assert( str.substr( pos1, 2 ) == "LL" );
str.replace( pos1, 3, "YDAY" ); // HE...!!!
assert( str == "HEYDAY!!!" ); // '-----pos1
return 0;
}
For more information, see CIS-62 std::string coverage.