C ++ iterator, const_iterator and const iterator (7)

Vector is only one type in the container.
All the standard library containers define the corresponding iterator type. The iterator applies to all containers. Modern C ++ programs prefer to use the iterator instead of subscript operations to access container elements.

1.Iterator, const_iterator: traverses elements in the container and accesses the values of these elements. Iterator can change the element value, but const_iterator cannot. The pointer to C is a bit like
(Containers can + ITER, while vector can also ITER-N, ITER + n, n is an integer, iter1-iter2: The result is difference_type, the distance between the two elements of the table .)

2.The const_iterator object can be used for const vector or non-const vector. its own value can be changed (it can point to other elements), but it cannot rewrite the element value it points.

3.Const iterator is different from const_iterator: It must be initialized when a const iterator is declared. Once initialized, it cannot be changed. Once initialized, it can only be used

Instead of directing it to other elements. (Therefore, const iterator is useless)

Example: vector <int> Nums (10); // Nums is nonconst
Const vector <int >:: iterator CIT = nums. Begin ();
* CIT = 1; // OK: CIT can change its underlying element
++ Cit; // error: Can't change the value of CIT

 

For example, read a piece of text into a vector object. Each word is stored as an element in the vector. Converts each word in a vector object to a lowercase letter. Output the converted elements in a vector object. Each eight words are output in one row.

-- From C ++ primer 3.14
// A self-written code passed the test in vs2008. Because vc6.0 does not support the Standard C ++, You need to modify the preprocessing to test the code.
// Subscripts
# Include <iostream>
# Include <string>
# Include <vector>
Using STD: vector;
Using STD: string;
Using STD: cout;
Using STD: CIN;
Using STD: Endl;
Int main ()
{
Vector <string> SVEC;
String word;
While (CIN> word)
SVEC. push_back (Word );
For (vector <string >:: size_type IX = 0; ix! = SVEC. Size (); ++ IX)
{
For (string: size_type Index = 0; index! = SVEC [ix]. Size (); ++ index) // Note: The return type of SVEC [ix]. Size () is string: size_type.
{
SVEC [ix] [Index] = tolower (SVEC [ix] [Index]);
}
}
For (vector <string >:: size_type IX = 0; ix! = SVEC. Size (); ++ IX)
{
Cout <SVEC [ix] <'';
If (IX + 1) % 8 = 0)
{
Cout <Endl;
}
}
Getchar ();
Return 0;

}
// Use iterator to improve...
Int main ()
{
Vector <string> SVEC;
String word;
While (CIN> word)
SVEC. push_back (Word );

For (vector <string >:: iterator iter = SVEC. Begin (); iter! = SVEC. End (); ++ ITER)// Apply iterator for rewriting
For (string: iterator iter2 = (* ITER). Begin (); iter2! = (* ITER). End (); ++ iter2)
* Iter2 = tolower (* iter2 );
// The above two lines of code are also changed to: For (string: size_type Index = 0; index! = (* ITER). Size (); ++ index)
// But it is not recommended (* ITER) [Index] = tolower (* ITER) [Index]);
Int IX = 0;
For (vector <string >:: const_iterator iter = SVEC. Begin (); iter! = SVEC. End (); ++ ITER, ++ IX)// Const_iterator is available for reading only
{
Cout <* ITER <'';
If (IX + 1) % 8 = 0)
{
Cout <Endl;
}
}
Getchar ();
Return 0;
}