{"id":2177,"date":"2025-01-28T19:46:48","date_gmt":"2025-01-28T19:46:48","guid":{"rendered":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/?page_id=2177"},"modified":"2025-01-28T21:37:41","modified_gmt":"2025-01-28T21:37:41","slug":"iterators","status":"publish","type":"page","link":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/topics\/c-details\/the-standard-template-library-2\/iterators\/","title":{"rendered":"Iterators"},"content":{"rendered":"\n

<\/span>Iterators<\/span><\/h2>\n\n\n\n

An iterator is an object (like a pointer) that points to an element inside the container.<\/em> <\/p>\n\n\n\n

We can use iterators to move through the contents of the container. They can be seen as something similar to a pointer pointing to some location and, using them, we can access content at that particular location.<\/p>\n\n\n\n

Iterators<\/em> are key to using STL effectively.<\/p>\n\n\n\n

One kind of iterator is an ordinary C++ pointer<\/strong><\/em>.  We were using a C++ pointer iterator in the code:<\/p>\n\n\n\n

\n
\n
<\/path><\/path><\/svg><\/span>
char<\/span> s[] = <\/span>"Example of generic find algorithm"<\/span>;<\/span><\/span>\nint<\/span> len = <\/span>strlen<\/span>(s);<\/span><\/span>\nconst<\/span> <\/span>char<\/span> *foundChar = <\/span>find<\/span>(&<\/span>s<\/span>[<\/span>0<\/span>], &<\/span>s<\/span>[len], <\/span>'g'<\/span>);<\/span><\/span>\nstd<\/span>::cout << <\/span>"Found character: "<\/span> << *foundChar << <\/span>std<\/span>::endl<\/span><\/span>\n\t        << <\/span>"Next character: "<\/span> << *(foundChar+<\/span>1<\/span>) << <\/span>std<\/span>::endl;<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n\n\n\n
<\/div>\n<\/div>\n\n\n\n
There are other kinds of iterators, but they are required to behave in a way similar to pointers. <\/p>\n\n\n\n
For example, the operator *<\/code><\/strong> dereferences the iterator to the value to which it refers.<\/p>\n\n\n\n
We were using other kinds of iterator in the code:<\/p>\n\n\n\n
\n
\n
<\/path><\/path><\/svg><\/span>
std<\/span>::vector<<\/span>char<\/span>> v = make< <\/span>std<\/span>::vector<<\/span>char<\/span>> ><\/span><\/span>\n(<\/span>"Example of generic find algorithm"<\/span>);<\/span><\/span>\n<\/span>\nstd<\/span>::<\/span>vector<\/span><<\/span>char<\/span>>::iterator foundChar <\/span><\/span>\n\t\t\t= <\/span>find<\/span>(<\/span>v<\/span>.<\/span>begin<\/span>(), <\/span>v<\/span>.<\/span>end<\/span>(), <\/span>'g'<\/span>);<\/span><\/span>\n\t\t\t<\/span><\/span>\nstd<\/span>::cout << <\/span>"Found character: "<\/span> << *foundChar << <\/span>std<\/span>::endl<\/span><\/span>\n\t        << <\/span>"Next character: "<\/span> << *(foundChar+<\/span>1<\/span>) << <\/span>std<\/span>::endl;<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n\n\n\n
<\/div>\n<\/div>\n\n\n\n
<\/span>Example using accumulate()<\/span><\/h3>\n\n\n\n
Here’s an example of using an Iterator with the Generic Algorithm accumulate()<\/strong><\/p>\n\n\n\n
accumulate()<\/strong> returns the result of accumulating all the values in the specified range.<\/p>\n\n\n\n
\n
\n
<\/path><\/path><\/svg><\/span>
\/\/<\/span><\/span>\n\/\/  main.cpp<\/span><\/span>\n\/\/  STL Iterators<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 10\/21\/24.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#include<\/span> <\/span><iostream><\/span><\/span>\n#include<\/span> <\/span><vector><\/span>   <\/span>\/\/ For vector<\/span><\/span>\n#include<\/span> <\/span><numeric><\/span>  <\/span>\/\/ For accumulate()<\/span><\/span>\n<\/span>\nint<\/span> <\/span>main<\/span>(<\/span>int<\/span> <\/span>argc<\/span>, <\/span>const<\/span> <\/span>char<\/span> <\/span>*<\/span> <\/span>argv<\/span>[])<\/span><\/span>\n{<\/span><\/span>\n  <\/span>int<\/span> values[] = {<\/span>2<\/span>, <\/span>3<\/span>, <\/span>5<\/span>, <\/span>7<\/span>, <\/span>11<\/span>};<\/span><\/span>\n  <\/span>int<\/span> len = <\/span>sizeof<\/span>(values)\/<\/span>sizeof<\/span>(<\/span>values<\/span>[<\/span>0<\/span>]);<\/span><\/span>\n  <\/span><\/span>\n  \/\/ Initialize vector using pointer iterator<\/span><\/span>\n  <\/span>std<\/span>::vector<<\/span>int<\/span>> <\/span>v<\/span>(&<\/span>values<\/span>[<\/span>0<\/span>], &<\/span>values<\/span>[len]);<\/span><\/span>\n<\/span>\n  <\/span>int<\/span> sum = <\/span>accumulate<\/span>(<\/span>v<\/span>.<\/span>begin<\/span>(), <\/span>v<\/span>.<\/span>end<\/span>(), <\/span>0<\/span>);<\/span><\/span>\n<\/span>\n  <\/span>std<\/span>::cout << <\/span>"Result: "<\/span> << sum << <\/span>std<\/span>::endl;<\/span><\/span>\n<\/span>\n  <\/span>return<\/span> <\/span>0<\/span>;<\/span><\/span>\n}<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n\n\n\n
\n
… which outputs:<\/p>\n\n\n\n
Result: 28\nProgram ended with exit code: 0<\/strong><\/code><\/pre>\n<\/div>\n<\/div>\n\n\n\n
<\/span>Iterator Categories<\/span><\/h3>\n\n\n\n
\n
\n
There are several categories of iterators:<\/p>\n\n\n\n