{"id":2065,"date":"2025-01-27T19:56:18","date_gmt":"2025-01-27T19:56:18","guid":{"rendered":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/?page_id=2065"},"modified":"2025-01-27T21:21:17","modified_gmt":"2025-01-27T21:21:17","slug":"using-arguments-to-specify-policy","status":"publish","type":"page","link":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/topics\/c-details\/function-templates-2\/using-arguments-to-specify-policy\/","title":{"rendered":"Using Arguments to Specify Policy"},"content":{"rendered":"\n

Using Arguments to Specify Policy<\/h2>\n\n\n\n

Consider the earlier sort<\/strong> function template:<\/p>\n\n\n\n

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<\/path><\/path><\/svg><\/span>
\/\/<\/span><\/span>\n\/\/  templbubble.h<\/span><\/span>\n\/\/  Function Templates<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 10\/11\/24.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#ifndef<\/span> templbubble_h<\/span><\/span>\n#define<\/span> templbubble_h<\/span><\/span>\n<\/span>\n#include<\/span> <\/span><vector><\/span><\/span>\n<\/span>\ntemplate<\/span><<\/span>typename<\/span> <\/span>TYPE<\/span>><\/span><\/span>\nvoid<\/span> <\/span>sort<\/span>(<\/span>std<\/span>::<\/span>vector<\/span><<\/span>TYPE<\/span>> <\/span>&<\/span>v<\/span>)<\/span><\/span>\n{<\/span><\/span>\n  <\/span>size_t<\/span> n = <\/span>v<\/span>.<\/span>size<\/span>();<\/span><\/span>\n  <\/span>for<\/span> (<\/span>size_t<\/span> i = <\/span>0<\/span>; i < n - <\/span>1<\/span>; i++)<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>for<\/span> (<\/span>size_t<\/span> j = n - <\/span>1<\/span>; i < j; j--)<\/span><\/span>\n    {<\/span><\/span>\n      <\/span>if<\/span> (<\/span>v<\/span>[j] < <\/span>v<\/span>[j - <\/span>1<\/span>])<\/span><\/span>\n      {<\/span>  \/\/ swap v[j] and v[j-1]<\/span><\/span>\n        TYPE temp = <\/span>v<\/span>[j];<\/span><\/span>\n        <\/span>v<\/span>[j] = <\/span>v<\/span>[j-<\/span>1<\/span>];<\/span><\/span>\n        <\/span>v<\/span>[j - <\/span>1<\/span>] = temp;<\/span><\/span>\n      }<\/span><\/span>\n    }<\/span><\/span>\n  }<\/span><\/span>\n}<\/span><\/span>\n<\/span>\n#endif<\/span> \/* templbubble_h *\/<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n\n\n\n
<\/div>\n<\/div>\n\n\n\n
What if we wanted to sort strings based on some other kind of collating sequence?  For example, in a case-insensitive order, or in reverse order.<\/p>\n\n\n\n
The sort algorithm doesn’t change.  Only the comparison needs to change from:<\/p>\n\n\n\n
if (v[j] < v[j - 1])<\/strong><\/code><\/pre>\n\n\n\n
We simply need to generalize this to a compare<\/strong> operation, and then provide a mechanism to pass in the desired compare operation.<\/p>\n\n\n\n
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<\/path><\/path><\/svg><\/span>
\/\/<\/span><\/span>\n\/\/  PolicySort.h<\/span><\/span>\n\/\/  Function Overload Resolution<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 10\/13\/24.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#ifndef<\/span> PolicySort_h<\/span><\/span>\n#define<\/span> PolicySort_h<\/span><\/span>\n<\/span>\n#include<\/span> <\/span><vector><\/span><\/span>\n<\/span>\ntemplate<\/span><<\/span>typename<\/span> <\/span>TYPE<\/span>, <\/span>typename<\/span> <\/span>C<\/span>><\/span><\/span>\nvoid<\/span> <\/span>sort<\/span>(<\/span>std<\/span>::<\/span>vector<\/span><<\/span>TYPE<\/span>> <\/span>&<\/span>v<\/span>)<\/span><\/span>\n{<\/span><\/span>\n  <\/span>size_t<\/span> n = <\/span>v<\/span>.<\/span>size<\/span>();<\/span><\/span>\n  <\/span>for<\/span> (<\/span>size_t<\/span> i = <\/span>0<\/span>; i < n - <\/span>1<\/span>; i++)<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>for<\/span> (<\/span>size_t<\/span> j = n - <\/span>1<\/span>; i < j; j--)<\/span><\/span>\n    {<\/span><\/span>\n      <\/span>if<\/span> (<\/span>C<\/span>::<\/span>compare<\/span>(<\/span>v<\/span>[j], <\/span>v<\/span>[j - <\/span>1<\/span>]) < <\/span>0<\/span>)<\/span><\/span>\n      {<\/span>  \/\/ swap v[j] and v[j-1]<\/span><\/span>\n        TYPE temp = <\/span>v<\/span>[j];<\/span><\/span>\n        <\/span>v<\/span>[j] = <\/span>v<\/span>[j-<\/span>1<\/span>];<\/span><\/span>\n        <\/span>v<\/span>[j - <\/span>1<\/span>] = temp;<\/span><\/span>\n      }<\/span><\/span>\n    }<\/span><\/span>\n  }<\/span><\/span>\n}<\/span><\/span>\n<\/span>\n#endif<\/span> \/* PolicySort_h *\/<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n\n\n\n
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Here’s a class, Compare<\/strong>, with the necessary compare()<\/strong> class function:<\/p>\n\n\n\n
<\/path><\/path><\/svg><\/span>
\/\/<\/span><\/span>\n\/\/  PolicyCompare.h<\/span><\/span>\n\/\/  Function Overload Resolution<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 10\/13\/24.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#ifndef<\/span> PolicyCompare_h<\/span><\/span>\n#define<\/span> PolicyCompare_h<\/span><\/span>\n<\/span>\n\/\/ A 'policy' class<\/span><\/span>\nclass<\/span> <\/span>Compare<\/span><\/span>\n{<\/span><\/span>\npublic:<\/span><\/span>\n  <\/span>static<\/span> <\/span>int<\/span> <\/span>compare<\/span>(<\/span>const<\/span> <\/span>char<\/span> <\/span>*<\/span>s1<\/span>, <\/span>const<\/span> <\/span>char<\/span> <\/span>*<\/span>s2<\/span>)<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>return<\/span> <\/span>strcmp<\/span>(s1, s2);<\/span>  \/\/ compare in the normal way<\/span><\/span>\n  }<\/span><\/span>\n};<\/span><\/span>\n<\/span>\n#endif<\/span> \/* PolicyCompare_h *\/<\/span><\/span>\n<\/span><\/code><\/pre><\/div>\n<\/div>\n<\/div>\n\n\n\n
Finally, here’s a main program to exercise this:<\/p>\n\n\n\n
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<\/path><\/path><\/svg><\/span>
\/\/<\/span><\/span>\n\/\/  PolicySort.cpp<\/span><\/span>\n\/\/  Function Overload Resolution<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 10\/13\/24.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#include<\/span> <\/span><iostream><\/span><\/span>\n#include<\/span> <\/span>"PolicySort.h"<\/span><\/span>\n#include<\/span> <\/span>"PolicyCompare.h"<\/span><\/span>\n<\/span>\nvoid<\/span> <\/span>printVector<\/span>(<\/span>std<\/span>::<\/span>vector<\/span><<\/span>const<\/span> <\/span>char<\/span> *> <\/span>v<\/span>)<\/span><\/span>\n{<\/span><\/span>\n  <\/span>for<\/span>(<\/span>int<\/span> i = <\/span>0<\/span>; i < <\/span>v<\/span>.<\/span>size<\/span>(); i++)<\/span><\/span>\n    <\/span>std<\/span>::cout << <\/span>' '<\/span> << <\/span>v<\/span>[i] << <\/span>std<\/span>::endl;<\/span><\/span>\n}<\/span><\/span>\n<\/span>\nint<\/span> <\/span>main<\/span>()<\/span><\/span>\n{<\/span><\/span>\n  <\/span>std<\/span>::vector<<\/span>const<\/span> <\/span>char<\/span> *> <\/span>vstrs<\/span>(<\/span>10<\/span>);<\/span><\/span>\n  <\/span><\/span>\n  <\/span>vstrs<\/span>[<\/span>0<\/span>] = <\/span>"Vera"<\/span>;<\/span><\/span>\n  <\/span>vstrs<\/span>[<\/span>1<\/span>] = <\/span>"mary"<\/span>;<\/span><\/span>\n  <\/span>vstrs<\/span>[<\/span>2<\/span>] = <\/span>"fred"<\/span>;<\/span><\/span>\n  <\/span>vstrs<\/span>[<\/span>3<\/span>] = <\/span>"Zena"<\/span>;<\/span><\/span>\n  <\/span>vstrs<\/span>[<\/span>4<\/span>] = <\/span>"Algernon"<\/span>;<\/span><\/span>\n  <\/span>vstrs<\/span>[<\/span>5<\/span>] = <\/span>"carol"<\/span>;<\/span><\/span>\n  <\/span>vstrs<\/span>[<\/span>6<\/span>] = <\/span>"alan"<\/span>;<\/span><\/span>\n  <\/span>vstrs<\/span>[<\/span>7<\/span>] = <\/span>"Richard"<\/span>;<\/span><\/span>\n  <\/span>vstrs<\/span>[<\/span>8<\/span>] = <\/span>"Beatrice"<\/span>;<\/span><\/span>\n  <\/span>vstrs<\/span>[<\/span>9<\/span>] = <\/span>"xavier"<\/span>;<\/span><\/span>\n<\/span>\n  <\/span>std<\/span>::cout << <\/span>"Before sorting: "<\/span> << <\/span>std<\/span>::endl;<\/span><\/span>\n  <\/span>printVector<\/span>(vstrs);<\/span><\/span>\n<\/span>\n  <\/span>sort<\/span><<\/span>const<\/span> <\/span>char<\/span> *, <\/span>Compare<\/span>>(vstrs);<\/span><\/span>\n    <\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>"After sorting: "<\/span> << <\/span>std<\/span>::endl;<\/span><\/span>\n  <\/span>printVector<\/span>(vstrs);<\/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
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… which produces the following:<\/p>\n\n\n\n
Before sorting: \n Vera\n mary\n fred\n Zena\n Algernon\n carol\n alan\n Richard\n Beatrice\n xavier\nAfter sorting: \n Algernon\n Beatrice\n Richard\n Vera\n Zena\n alan\n carol\n fred\n mary\n xavier\nProgram ended with exit code: 0<\/strong><\/code><\/pre>\n<\/div>\n<\/div>\n\n\n\n
If we change the Compare<\/strong> class as follows:<\/p>\n\n\n\n
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<\/path><\/path><\/svg><\/span>
\/\/<\/span><\/span>\n\/\/  PolicyCompare.h<\/span><\/span>\n\/\/  Function Overload Resolution<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 10\/13\/24.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#ifndef<\/span> PolicyCompare_h<\/span><\/span>\n#define<\/span> PolicyCompare_h<\/span><\/span>\n<\/span>\n\/\/ A 'policy' class<\/span><\/span>\nclass<\/span> <\/span>Compare<\/span><\/span>\n{<\/span><\/span>\npublic:<\/span><\/span>\n  <\/span>static<\/span> <\/span>int<\/span> <\/span>compare<\/span>(<\/span>const<\/span> <\/span>char<\/span> <\/span>*<\/span>s1<\/span>, <\/span>const<\/span> <\/span>char<\/span> <\/span>*<\/span>s2<\/span>)<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>return<\/span> -<\/span>strcmp<\/span>(s1, s2);<\/span>\t\/\/ reverse compare<\/span><\/span>\n  }<\/span><\/span>\n};<\/span><\/span>\n<\/span>\n#endif<\/span> \/* PolicyCompare_h *\/<\/span><\/span>\n<\/span><\/code><\/pre><\/div>\n<\/div>\n\n\n\n
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Now, the program outputs the reversed sort order:<\/p>\n\n\n\n
Before sorting: \n Vera\n mary\n fred\n Zena\n Algernon\n carol\n alan\n Richard\n Beatrice\n xavier\nAfter sorting: \n xavier\n mary\n fred\n carol\n alan\n Zena\n Vera\n Richard\n Beatrice\n Algernon\nProgram ended with exit code: 0<\/strong><\/code><\/pre>\n<\/div>\n<\/div>\n\n\n\n
Similarly, we could simply pass in a different class with a different compare implementation to control sorting order in any way we wish.<\/p>\n\n\n\n
<\/div>\n\n\n\n
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Next: Default Template Parameters<\/a><\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"
Using Arguments to Specify Policy Consider the earlier sort function template: What if we wanted to sort strings based on some other kind of collating sequence?  For example, in a case-insensitive order, or in reverse order. The sort algorithm doesn’t change.  Only the comparison needs to change from: We simply need to generalize this to […]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":2029,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-2065","page","type-page","status-publish","hentry"],"blocksy_meta":[],"_links":{"self":[{"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/pages\/2065","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=2065"}],"version-history":[{"count":3,"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/pages\/2065\/revisions"}],"predecessor-version":[{"id":2097,"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/pages\/2065\/revisions\/2097"}],"up":[{"embeddable":true,"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/pages\/2029"}],"wp:attachment":[{"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/media?parent=2065"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}