{"id":2118,"date":"2025-01-27T21:57:30","date_gmt":"2025-01-27T21:57:30","guid":{"rendered":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/?page_id=2118"},"modified":"2025-01-28T19:06:56","modified_gmt":"2025-01-28T19:06:56","slug":"friend-declarations-in-class-templates","status":"publish","type":"page","link":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/topics\/c-details\/class-templates-2\/friend-declarations-in-class-templates\/","title":{"rendered":"friend Declarations in Class Templates"},"content":{"rendered":"\n

<\/span>friend Declarations in Class Templates<\/span><\/h2>\n\n\n\n

You can have three kinds of friend<\/strong> declarations within a class template:<\/p>\n\n\n\n

    \n
  • A non-template friend class or friend function<\/li>\n\n\n\n
  • A bound<\/em> friend class template or function template.<\/li>\n\n\n\n
  • An unbound<\/em> friend class template or function template<\/li>\n<\/ul>\n\n\n\n

    <\/span>A non-template friend class or friend function<\/span><\/h3>\n\n\n\n
    template <typename T>\nclass QueueItem\n{\n\tfriend class Mumble;\n\tfriend int bumble(double d);\n\tfriend char *Fumble::rumble();\n\t\/\/ \u2026\n};<\/strong><\/code><\/pre>\n\n\n\n
    In this example, class Mumble<\/strong>, function bumble()<\/strong>, and member function rumble()<\/strong> in class Fumble<\/strong> are friends to all instantiations of the class template<\/em> QueueItem<\/strong>.<\/p>\n\n\n\n
    <\/span>A bound<\/strong> friend class template or friend function<\/span><\/h3>\n\n\n\n
    template <typename T>\nclass QueueItem\n{\n\tfriend class Mumble<T>;\n\tfriend int bumble<T>( QueueItem<T> );\n\tfriend char *Fumble<T>::rumble();\n\t\/\/ \u2026\n};\n<\/strong><\/code><\/pre>\n\n\n\n
    In this example, the friends are all template instantiations based on the same type, T<\/strong>, as the enclosing class template, QueueItem<T><\/strong>.  <\/p>\n\n\n\n
    A 1-to-1 mapping is defined between the instantiation of the class template <\/em>QueueItem<T><\/strong> and the template instantiations of the friends<\/em>.<\/p>\n\n\n\n
    <\/span>An unbound<\/strong> friend class template or friend function<\/span><\/h3>\n\n\n\n
    template <typename T>\nclass QueueItem\n{\n\ttemplate <typename U>\n\tfriend class Mumble;\n\n\ttemplate <typename V>\n\tfriend int bumble( QueueItem<V> );\n\n\ttemplate <typename W>\n\tfriend char *Fumble<W>::rumble();\n\t\/\/ \u2026\n};<\/strong><\/code><\/pre>\n\n\n\n
    Here, the friends are all class templates based on types different from the type, T<\/strong>, of the enclosing class template, QueueItem<T><\/strong>. <\/p>\n\n\n\n
    A 1-to-many mapping is defined between the instantiation of the class template <\/em>QueueItem<T><\/strong> and the template instantiations of the friends<\/em>.  For each type instantiation of QueueItem<\/strong>, all instantiations of Mumble<\/strong>, bumble()<\/strong> and Fumble<W>::rumble()<\/strong> are friends.<\/p>\n\n\n\n
    <\/span>Using Friends in our Queue Class<\/span><\/h3>\n\n\n\n
    Let’s make some changes to our Queue class.<\/p>\n\n\n\n
    Note that the QueueItem<\/strong> class in our Queue<\/strong> example is not intended for use outside the Queue<\/strong> class. <\/p>\n\n\n\n
    We can enforce that by making its constructor private and specifying that the Queue<\/strong> class is a friend.<\/p>\n\n\n\n
    Nothing else needs to change. (The main function is the same.)<\/p>\n\n\n\n
    \n
    \n
    <\/path><\/path><\/svg><\/span>
    \/\/<\/span><\/span>\n\/\/  Queue.h<\/span><\/span>\n\/\/  Queue Template Class with friends<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 10\/17\/24.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#ifndef<\/span> Queue_h<\/span><\/span>\n#define<\/span> Queue_h<\/span><\/span>\n<\/span>\n#include<\/span> <\/span>"assert.h"<\/span><\/span>\n<\/span>\n\/\/ Forward declaration<\/span><\/span>\ntemplate<\/span> <<\/span>typename<\/span> <\/span>TYPE<\/span>><\/span><\/span>\nclass<\/span> <\/span>QueueItem<\/span>;<\/span><\/span>\n<\/span>\n\/\/ The Queue<\/span><\/span>\ntemplate<\/span> <<\/span>typename<\/span> <\/span>TYPE<\/span>><\/span><\/span>\nclass<\/span> <\/span>Queue<\/span><\/span>\n{<\/span><\/span>\npublic:<\/span><\/span>\n  <\/span>typedef<\/span> <\/span>void<\/span> <\/span>func_t<\/span>(QueueItem<TYPE> *qiPtr);<\/span><\/span>\n<\/span>\n  <\/span>Queue<\/span>()<\/span><\/span>\n    : <\/span>m_front<\/span>(<\/span>0<\/span>), <\/span>m_back<\/span>(<\/span>0<\/span>)<\/span><\/span>\n  {}<\/span><\/span>\n  <\/span><\/span>\n  <\/span>~Queue<\/span>()<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>while<\/span> (!<\/span>IsEmpty<\/span>())<\/span><\/span>\n      <\/span>RemoveFromFront<\/span>();<\/span><\/span>\n  }<\/span><\/span>\n  <\/span><\/span>\n  <\/span>void<\/span> <\/span>AddToBack<\/span>(<\/span>const<\/span> <\/span>TYPE<\/span> <\/span>&<\/span>value<\/span>)<\/span><\/span>\n  {<\/span><\/span>\n    QueueItem<TYPE> *qiPtr<\/span><\/span>\n      = <\/span>new<\/span> <\/span>QueueItem<\/span><<\/span>TYPE<\/span>>(value);<\/span><\/span>\n    <\/span>if<\/span> (<\/span>IsEmpty<\/span>())<\/span><\/span>\n      m_front = m_back = qiPtr;<\/span><\/span>\n    <\/span>else<\/span><\/span>\n    {<\/span><\/span>\n      <\/span>m_back<\/span>-><\/span>setNext<\/span>(qiPtr);<\/span><\/span>\n      m_back = qiPtr;<\/span><\/span>\n    }<\/span><\/span>\n  }<\/span><\/span>\n<\/span>\n  <\/span>const<\/span> <\/span>TYPE<\/span> <\/span>RemoveFromFront<\/span>()<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>if<\/span>(<\/span>IsEmpty<\/span>())<\/span><\/span>\n      <\/span>return<\/span> <\/span>0<\/span>;<\/span>  \/\/ Nothing to remove<\/span><\/span>\n<\/span>\n    QueueItem<TYPE> *qiPtr = m_front;<\/span><\/span>\n    m_front = <\/span>m_front<\/span>-><\/span>getNext<\/span>();<\/span><\/span>\n    <\/span>const<\/span> TYPE theValue = <\/span>qiPtr<\/span>-><\/span>getValue<\/span>();<\/span><\/span>\n    <\/span>delete<\/span> qiPtr;<\/span>  \/\/ Deallocate the QueueItem<\/span><\/span>\n    <\/span>return<\/span> theValue;<\/span><\/span>\n  }<\/span><\/span>\n<\/span>\n  <\/span>bool<\/span> <\/span>IsEmpty<\/span>() <\/span>const<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>return<\/span> m_front == <\/span>0<\/span>;<\/span><\/span>\n  }<\/span><\/span>\n  <\/span><\/span>\n  <\/span>void<\/span> <\/span>ForEachItem<\/span>(<\/span>func_t<\/span> <\/span>*<\/span>func<\/span>)<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>for<\/span> (QueueItem<TYPE> *qi = m_front;<\/span><\/span>\n        qi != <\/span>0<\/span>; qi = <\/span>qi<\/span>-><\/span>getNext<\/span>())<\/span><\/span>\n    {<\/span><\/span>\n      <\/span>func<\/span>(qi);<\/span><\/span>\n    }<\/span><\/span>\n  }<\/span><\/span>\n<\/span>\nprivate:<\/span><\/span>\n  QueueItem<TYPE> *m_front;<\/span><\/span>\n  QueueItem<TYPE> *m_back;<\/span><\/span>\n};<\/span><\/span>\n<\/span>\n\/\/ A Queue item<\/span><\/span>\ntemplate<\/span> <<\/span>typename<\/span> <\/span>TYPE<\/span>><\/span><\/span>\nclass<\/span> <\/span>QueueItem<\/span><\/span>\n{<\/span><\/span>\n  <\/span>friend<\/span> <\/span>class<\/span> <\/span>Queue<\/span><<\/span>TYPE<\/span>>;<\/span> \/\/ Make friends<\/span><\/span>\n  <\/span><\/span>\npublic:<\/span><\/span>\n  <\/span>const<\/span> <\/span>TYPE<\/span> <\/span>getValue<\/span>() <\/span>const<\/span><\/span>\n  { <\/span>return<\/span> m_item; }<\/span><\/span>\n  <\/span>QueueItem<\/span>*<\/span> <\/span>getNext<\/span>()<\/span><\/span>\n  { <\/span>return<\/span> m_next; }<\/span><\/span>\n  <\/span>void<\/span> <\/span>setNext<\/span>(<\/span>QueueItem<\/span>*<\/span> <\/span>next<\/span>)<\/span><\/span>\n  { m_next = next; }<\/span><\/span>\nprivate:<\/span><\/span>\n  <\/span>QueueItem<\/span>(<\/span>const<\/span> <\/span>TYPE<\/span> <\/span>&<\/span>item<\/span>)<\/span><\/span>\n    : <\/span>m_item<\/span>(item), <\/span>m_next<\/span>(<\/span>0<\/span>)<\/span><\/span>\n  {}<\/span><\/span>\n<\/span>\n  <\/span>const<\/span> TYPE   m_item;<\/span><\/span>\n  QueueItem  *m_next;<\/span><\/span>\n};<\/span><\/span>\n<\/span>\n#endif<\/span> \/* Queue_h *\/<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n\n\n\n
    \n
    <\/path><\/path><\/svg><\/span>
    \/\/<\/span><\/span>\n\/\/  main.cpp<\/span><\/span>\n\/\/  Queue Template Class<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 10\/17\/24.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#include<\/span> <\/span><iostream><\/span><\/span>\n#include<\/span> <\/span>"Queue.h"<\/span><\/span>\n<\/span>\nvoid<\/span> <\/span>displayItem<\/span>( <\/span>QueueItem<\/span><<\/span>int<\/span>> <\/span>*<\/span>qiPtr<\/span> )<\/span><\/span>\n{<\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>"QueueItem: "<\/span> << qiPtr<\/span><\/span>\n    << <\/span>" value = "<\/span><\/span>\n    << <\/span>qiPtr<\/span>-><\/span>getValue<\/span>() << <\/span>std<\/span>::endl;<\/span><\/span>\n}<\/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  Queue<<\/span>int<\/span>> queue;<\/span><\/span>\n<\/span>\n  <\/span>for<\/span> (<\/span>int<\/span> i = <\/span>0<\/span>; i < <\/span>5<\/span>; i++)<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>queue<\/span>.<\/span>AddToBack<\/span>(i*i);<\/span><\/span>\n            \/\/ The square of i<\/span><\/span>\n  }<\/span><\/span>\n  <\/span><\/span>\n  <\/span>queue<\/span>.<\/span>ForEachItem<\/span>(displayItem);<\/span><\/span>\n  <\/span><\/span>\n  <\/span>for<\/span> (<\/span>int<\/span> i = <\/span>0<\/span>; i < <\/span>5<\/span>; i++)<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>const<\/span> <\/span>int<\/span> value<\/span><\/span>\n          = <\/span>queue<\/span>.<\/span>RemoveFromFront<\/span>();<\/span><\/span>\n    <\/span>std<\/span>::cout << <\/span>"["<\/span> << i << <\/span>"] : "<\/span><\/span>\n              << value << <\/span>std<\/span>::endl;<\/span><\/span>\n  }<\/span><\/span>\n  <\/span><\/span>\n  <\/span>return<\/span> <\/span>0<\/span>;<\/span><\/span>\n}<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  main.cpp<\/span><\/span>\n\/\/  Template Nontype Parameters<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 10\/17\/24.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#include<\/span> <\/span><iostream><\/span><\/span>\n#include<\/span> <\/span>"CharArray.h"<\/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  CharArray<<\/span>8<\/span>> carray1;<\/span><\/span>\n<\/span>\n  <\/span>for<\/span> (<\/span>int<\/span> i = <\/span>0<\/span>; i < <\/span>carray1<\/span>.<\/span>getSize<\/span>(); i++)<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>carray1<\/span>[i] = <\/span>'a'<\/span> + i;<\/span><\/span>\n  }<\/span><\/span>\n<\/span>\n  <\/span>std<\/span>::cout << <\/span>"Array has "<\/span> << <\/span>carray1<\/span>.<\/span>getSize<\/span>()<\/span><\/span>\n            << <\/span>" elements"<\/span> << <\/span>std<\/span>::endl;<\/span><\/span>\n  <\/span>for<\/span> (<\/span>int<\/span> i = <\/span>0<\/span>; i < <\/span>carray1<\/span>.<\/span>getSize<\/span>(); i++)<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>std<\/span>::cout << <\/span>"["<\/span> << i << <\/span>"] : "<\/span> <\/span><\/span>\n              << <\/span>carray1<\/span>[i] << <\/span>std<\/span>::endl;<\/span><\/span>\n  }<\/span><\/span>\n  <\/span><\/span>\n  <\/span>return<\/span> <\/span>0<\/span>;<\/span><\/span>\n}<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
    which outputs:<\/p>\n\n\n\n
    QueueItem: 0x600000008020 value = 0\nQueueItem: 0x600000008030 value = 1\nQueueItem: 0x600000008040 value = 4\nQueueItem: 0x600000008050 value = 9\nQueueItem: 0x600000008060 value = 16\n[0] : 0\n[1] : 1\n[2] : 4\n[3] : 9\n[4] : 16\nProgram ended with exit code: 0<\/strong><\/code><\/pre>\n<\/div>\n<\/div>\n\n\n\n
    <\/span>Nested Types in Class Templates<\/span><\/h3>\n\n\n\n
    Even better:  Make QueueItem<\/strong> a nested private type within the Queue<\/strong> class:<\/p>\n\n\n\n
    \n
    \n
    <\/path><\/path><\/svg><\/span>
    \/\/<\/span><\/span>\n\/\/  Queue.h<\/span><\/span>\n\/\/  Queue Template Class with Nesting<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 10\/17\/24.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#ifndef<\/span> Queue_h<\/span><\/span>\n#define<\/span> Queue_h<\/span><\/span>\n<\/span>\n\/\/ The Queue<\/span><\/span>\ntemplate<\/span> <<\/span>typename<\/span> <\/span>TYPE<\/span>><\/span><\/span>\nclass<\/span> <\/span>Queue<\/span><\/span>\n{<\/span><\/span>\npublic:<\/span><\/span>\n  <\/span>typedef<\/span> <\/span>void<\/span> <\/span>func_t<\/span>(TYPE value);<\/span> \/\/ Note change of signature<\/span><\/span>\n<\/span>\n  <\/span>Queue<\/span>()<\/span><\/span>\n    : <\/span>m_front<\/span>(<\/span>0<\/span>), <\/span>m_back<\/span>(<\/span>0<\/span>)<\/span><\/span>\n  {}<\/span><\/span>\n  <\/span><\/span>\n  <\/span>~Queue<\/span>()<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>while<\/span> (!<\/span>IsEmpty<\/span>())<\/span><\/span>\n      <\/span>RemoveFromFront<\/span>();<\/span><\/span>\n  }<\/span><\/span>\n  <\/span><\/span>\n  <\/span>void<\/span> <\/span>AddToBack<\/span>(<\/span>const<\/span> <\/span>TYPE<\/span> <\/span>&<\/span>value<\/span>)<\/span><\/span>\n  {<\/span><\/span>\n    QueueItem *qiPtr<\/span><\/span>\n      = <\/span>new<\/span> <\/span>QueueItem<\/span>(value);<\/span> \/\/ Note removal of <TYPE><\/span><\/span>\n    <\/span>if<\/span> (<\/span>IsEmpty<\/span>())<\/span><\/span>\n      m_front = m_back = qiPtr;<\/span><\/span>\n    <\/span>else<\/span><\/span>\n    {<\/span><\/span>\n      <\/span>m_back<\/span>-><\/span>setNext<\/span>(qiPtr);<\/span><\/span>\n      m_back = qiPtr;<\/span><\/span>\n    }<\/span><\/span>\n  }<\/span><\/span>\n<\/span>\n  <\/span>const<\/span> <\/span>TYPE<\/span> <\/span>RemoveFromFront<\/span>()<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>if<\/span>(<\/span>IsEmpty<\/span>())<\/span><\/span>\n      <\/span>return<\/span> <\/span>0<\/span>;<\/span>  \/\/ Nothing to remove<\/span><\/span>\n<\/span>\n    QueueItem *qiPtr = m_front;<\/span> \/\/ Note removal of <TYPE><\/span><\/span>\n    m_front = <\/span>m_front<\/span>-><\/span>getNext<\/span>();<\/span><\/span>\n    <\/span>const<\/span> TYPE theValue = <\/span>qiPtr<\/span>-><\/span>getValue<\/span>();<\/span><\/span>\n    <\/span>delete<\/span> qiPtr;<\/span>  \/\/ Deallocate the QueueItem<\/span><\/span>\n    <\/span>return<\/span> theValue;<\/span><\/span>\n  }<\/span><\/span>\n<\/span>\n  <\/span>bool<\/span> <\/span>IsEmpty<\/span>() <\/span>const<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>return<\/span> m_front == <\/span>0<\/span>;<\/span><\/span>\n  }<\/span><\/span>\n  <\/span><\/span>\n  <\/span>void<\/span> <\/span>ForEachItem<\/span>(<\/span>func_t<\/span> <\/span>*<\/span>func<\/span>)<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>for<\/span> (QueueItem *qi = m_front;<\/span> \/\/ Note removal of <TYPE><\/span><\/span>\n        qi != <\/span>0<\/span>; qi = <\/span>qi<\/span>-><\/span>getNext<\/span>())<\/span><\/span>\n    {<\/span><\/span>\n      <\/span>func<\/span>(<\/span>qi<\/span>-><\/span>getValue<\/span>());<\/span><\/span>\n    }<\/span><\/span>\n  }<\/span><\/span>\n<\/span>\nprivate:<\/span><\/span>\n  \/\/ A Queue item, now private<\/span><\/span>\n  <\/span>class<\/span> <\/span>QueueItem<\/span> <\/span>\/\/ Note removal of <TYPE><\/span><\/span>\n  {<\/span><\/span>\n  <\/span>public:<\/span><\/span>\n    <\/span>QueueItem<\/span>(<\/span>const<\/span> <\/span>TYPE<\/span> <\/span>&<\/span>item<\/span>)<\/span><\/span>\n      : <\/span>m_item<\/span>(item), <\/span>m_next<\/span>(<\/span>0<\/span>)<\/span><\/span>\n    {}<\/span><\/span>\n<\/span>\n    <\/span>const<\/span> <\/span>TYPE<\/span> <\/span>getValue<\/span>() <\/span>const<\/span><\/span>\n    { <\/span>return<\/span> m_item; }<\/span><\/span>\n    <\/span>QueueItem<\/span>*<\/span> <\/span>getNext<\/span>()<\/span><\/span>\n    { <\/span>return<\/span> m_next; }<\/span><\/span>\n    <\/span>void<\/span> <\/span>setNext<\/span>(<\/span>QueueItem<\/span>*<\/span> <\/span>next<\/span>)<\/span><\/span>\n    { m_next = next; }<\/span><\/span>\n    <\/span><\/span>\n  <\/span>private:<\/span><\/span>\n    <\/span>const<\/span> TYPE  m_item;<\/span><\/span>\n    QueueItem  *m_next;<\/span><\/span>\n  };<\/span><\/span>\n<\/span>\n  QueueItem *m_front;<\/span> \/\/ Note removal of <TYPE><\/span><\/span>\n  QueueItem *m_back;<\/span>  \/\/ Note removal of <TYPE><\/span><\/span>\n};<\/span><\/span>\n<\/span>\n#endif<\/span> \/* Queue_h *\/<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n\n\n\n
    \n
    We had to change the main program:<\/p>\n\n\n\n
    <\/path><\/path><\/svg><\/span>
    \/\/<\/span><\/span>\n\/\/  main.cpp<\/span><\/span>\n\/\/  Queue Template Class with Nesting<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 10\/17\/24.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#include<\/span> <\/span><iostream><\/span><\/span>\n#include<\/span> <\/span>"Queue.h"<\/span><\/span>\n<\/span>\nvoid<\/span> <\/span>displayItem<\/span>( <\/span>int<\/span> <\/span>value<\/span> )<\/span><\/span>\n{<\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>' '<\/span> << value;<\/span><\/span>\n}<\/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  Queue<<\/span>int<\/span>> queue;<\/span><\/span>\n<\/span>\n  <\/span>for<\/span> (<\/span>int<\/span> i = <\/span>0<\/span>; i < <\/span>5<\/span>; i++)<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>queue<\/span>.<\/span>AddToBack<\/span>(i*i);<\/span><\/span>\n            \/\/ The square of i<\/span><\/span>\n  }<\/span><\/span>\n  <\/span><\/span>\n  <\/span>queue<\/span>.<\/span>ForEachItem<\/span>(displayItem);<\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>std<\/span>::endl;<\/span><\/span>\n  <\/span><\/span>\n  <\/span>for<\/span> (<\/span>int<\/span> i = <\/span>0<\/span>; i < <\/span>5<\/span>; i++)<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>const<\/span> <\/span>int<\/span> value<\/span><\/span>\n          = <\/span>queue<\/span>.<\/span>RemoveFromFront<\/span>();<\/span><\/span>\n    <\/span>std<\/span>::cout << <\/span>"["<\/span> << i << <\/span>"] : "<\/span><\/span>\n              << value << <\/span>std<\/span>::endl;<\/span><\/span>\n  }<\/span><\/span>\n  <\/span><\/span>\n  <\/span>return<\/span> <\/span>0<\/span>;<\/span><\/span>\n}<\/span><\/span>\n<\/span><\/code><\/pre><\/div>\n\n\n\n
    which outputs:<\/p>\n\n\n\n
     0 1 4 9 16\n[0] : 0\n[1] : 1\n[2] : 4\n[3] : 9\n[4] : 16\nProgram ended with exit code: 0<\/strong><\/code><\/pre>\n<\/div>\n<\/div>\n\n\n\n
    <\/div>\n\n\n\n
    \n
    Next: operator<< for Class Templates<\/a><\/div>\n<\/div>\n\n\n\n
    <\/p>\n","protected":false},"excerpt":{"rendered":"
    friend Declarations in Class Templates You can have three kinds of friend declarations within a class template: A non-template friend class or friend function In this example, class Mumble, function bumble(), and member function rumble() in class Fumble are friends to all instantiations of the class template QueueItem. A bound friend class template or friend […]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":2103,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-2118","page","type-page","status-publish","hentry"],"blocksy_meta":[],"_links":{"self":[{"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/pages\/2118","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/comments?post=2118"}],"version-history":[{"count":3,"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/pages\/2118\/revisions"}],"predecessor-version":[{"id":2146,"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/pages\/2118\/revisions\/2146"}],"up":[{"embeddable":true,"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/pages\/2103"}],"wp:attachment":[{"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/media?parent=2118"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}