deque::operator[] and deque::at
Illustrates how to use the deque::operator[] and deque::at Standard Template Library (STL) functions in Visual C++.
const_reference operator[](
size_type Pos
) const;
reference operator[](
size_type Pos
);
const_reference operator[](
difference_type _N
) const;
reference operator[](
difference_type _N
) const;
const_reference at(
size_type Pos
) const;
reference at(
size_type Pos
); bool empty( ) const;
Remarks
注意
The class/parameter names in the prototype do not match the version in the header file. Some have been modified to improve readability.
The operator[] member function returns a reference to the element of the controlled sequence at position Pos. If that position is invalid, the behavior is undefined. The at member function returns a reference to the element of the controlled sequence at position Pos. If that position is invalid, the function throws an object of class out_of_range. The empty member function returns true for an empty controlled sequence.
Example
// operator.cpp
// compile with: /EHsc
//
// Functions:
// operator[]
// at
// empty
// push_back
// begin
// end
#include <iostream>
#include <deque>
using namespace std;
typedef deque<char > CHARDEQUE;
void print_contents (CHARDEQUE deque, char*);
int main()
{
//create an empty deque a
CHARDEQUE a;
//check whether it is empty
if(a.empty())
cout<<"a is empty"<<endl;
else
cout<<"a is not empty"<<endl;
//inset A, B, C and D to a
a.push_back('A');
a.push_back('B');
a.push_back('C');
a.push_back('D');
//check again whether a is empty
if(a.empty())
cout<<"a is empty"<<endl;
else
cout<<"a is not empty"<<endl;
//print out the contents
print_contents (a,"a");
cout <<"The first element of a is " <<a[0] <<endl;
cout <<"The first element of a is " <<a.at(0) <<endl;
cout <<"The last element of a is " <<a[a.size()-1] <<endl;
cout <<"The last element of a is " <<a.at(a.size()-1) <<endl;
}
//function to print the contents of deque
void print_contents (CHARDEQUE deque, char *name)
{
CHARDEQUE::iterator pdeque;
cout <<"The contents of "<< name <<" :";
for(pdeque = deque.begin();
pdeque != deque.end();
pdeque++)
{
cout <<" " << *pdeque;
}
cout<<endl;
}
a is empty
a is not empty
The contents of a : A B C D
The first element of a is A
The first element of a is A
The last element of a is D
The last element of a is D
Requirements
Header: < deque>