C++ Vectors

C++ Vectors<?XML:NAMESPACE PREFIX = O />

 

Constructors

 

Syntax:

 

vector();   vector( size_type num, const TYPE &val );   vector( const vector &from );   vector( input_iterator start, input_iterator end );

C++ Vectors can be constructed with either:

 

· Nothing - which creates an empty vector,

 

· num and val - puts num copies of val in the vector,

 

· from - creates a vector with the same contents as from, or

 

· start and end - which creates a vector containing elements from start to end.

 

For example, the following example constructs a vector consisting of five copies of the integer 42.

 

vector<int> v1( 5, 42 );
 

at

 

Syntax: 
 

TYPE at( size_type loc );

The at() function returns a reference to the element in the current vector at loc. The at() function is safer than the [] operator, because it won't let you reference items outside the bounds of the vector. For example, consider the following code:

 

vector<int> v( 5, 1 );
 

for( int i = 0; i < 10; i++ ) {
 

 cout << "Element " << i << " is " << v[i] << endl;
 

}
 

This code overrunns the end of the vector, producing potentially dangerous results. The following code would be much safer:

 

vector<int> v( 5, 1 );
 

for( int i = 0; i < 10; i++ ) {
 

 cout << "Element " << i << " is " << v.at(i) << endl;
 

}
 

Instead of attempting to read garbage values from memory, the at() function will realize that it is about to overrun the vector and will throw an exception.

 

erase

 

Syntax:

 

iterator erase( iterator loc );   iterator erase( iterator start, iterator end );

The erase() function either deletes the element at location loc, or deletes the elements between start and end. The return value is the element after the last element erased. For example:

 

// Create a vector, load it with the first ten characters of the alphabet
 

vector<char> alphaVector;
 

for( int i=0; i < 10; i++ )
 

 alphaVector.push_back( i + 65 );
 

int size = alphaVector.size();
 

vector<char>::iterator startIterator;
 

vector<char>::iterator tempIterator;
 

for( int i=0; i < size; i++ ) {
 

 startIterator = alphaVector.begin();
 

 alphaVector.erase( startIterator );
 

 // Display the vector
 

 for( tempIterator = alphaVector.begin(); tempIterator != alphaVector.end(); tempIterator++ )
 

 cout << *tempIterator;
 

 cout << endl;
 

}
 

That code would display the following output:

 

BCDEFGHIJ
 

CDEFGHIJ
 

DEFGHIJ
 

EFGHIJ
 

FGHIJ
 

GHIJ
 

HIJ
 

IJ
 

J
 

pop_back

 

Syntax: 
 

void pop_back();

The function pop_back() deletes the last element in the current vector. For example:

 

vector<char> alphaVector;
 

for( int i=0; i < 10; i++ )
 

 alphaVector.push_back( i + 65 );
 

int size = alphaVector.size();
 

vector<char>::iterator theIterator;
 

for( int i=0; i < size; i++ ) {
 

 alphaVector.pop_back();
 

 for( theIterator = alphaVector.begin(); theIterator != alphaVector.end(); theIterator++ )
 

 cout << *theIterator;
 

 cout << endl;
 

}
 

This code displays the following output:

 

ABCDEFGHI
 

ABCDEFGH
 

ABCDEFG
 

ABCDEF
 

ABCDE
 

ABCD
 

ABC
 

AB
 

A
 

Related topics:
erase(). 
 

push_back

 

Syntax: 
 

void push_back( const TYPE &val );

The push_back() function appends val to the end of the current vector.

 

insert

 

Syntax: 
 

iterator insert( iterator loc, const TYPE &val );   void insert( iterator loc, size_type num, const TYPE &val );   void insert( iterator loc, input_iterator start, input_iterator end );

The function insert() either:

 

· inserts val before loc, returning an iterator to that element, 
 

· inserts num copies of val before loc, or 
 

· inserts the elements from start to end before loc. 
 

For example: 
 

// Create a vector, load it with the first 10 characters of the alphabet
 

vector<char> alphaVector;
 

for( int i=0; i < 10; i++ )
 

 alphaVector.push_back( i + 65 );
 

// Insert four C's into the vector
 

vector<char>::iterator theIterator = alphaVector.begin();
 

alphaVector.insert( theIterator, 4, 'C' );
 

// Display the vector
 

for( theIterator = alphaVector.begin(); theIterator != alphaVector.end(); theIterator++ )
 

 cout << *theIterator;
 

This code would display:

 

CCCCABCDEFGHIJ
 

size

 

Syntax: 
 

size_type size();

The size() function returns the number of elements in the current vector.