{"id":2070,"date":"2025-01-27T20:02:48","date_gmt":"2025-01-27T20:02:48","guid":{"rendered":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/?page_id=2070"},"modified":"2025-01-27T21:23:23","modified_gmt":"2025-01-27T21:23:23","slug":"default-template-parameters","status":"publish","type":"page","link":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/topics\/c-details\/function-templates-2\/default-template-parameters\/","title":{"rendered":"Default Template Parameters"},"content":{"rendered":"\n

Default Template Parameters<\/h2>\n\n\n\n

Rather than force you always to specify the Comp<\/strong> class explicitly, it would be nice to be able to default it to the most common case.<\/p>\n\n\n\n

You can do this by supplying two function templates:<\/p>\n\n\n\n

template<typename T, typename C>\n\tvoid sort(vector<T> &v);\ntemplate<typename T>\n\tvoid sort(vector<T> &v<\/strong>);<\/code><\/pre>\n\n\n\n
More conveniently, you can use default template parameters<\/em>:<\/p>\n\n\n\n
template<typename T, typename C = Comp>\nvoid sort(vector<T> &v);<\/strong><\/code><\/pre>\n\n\n\n
So, with some minor changes to a couple of files, and an additional file:<\/p>\n\n\n\n
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\/\/<\/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#include<\/span> <\/span>"PolicyCompare.h"<\/span><\/span>\n<\/span>\ntemplate<\/span><<\/span>typename<\/span> <\/span>TYPE<\/span>, <\/span>typename<\/span> <\/span>C<\/span> = Compare><\/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\n\n\n
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\/\/<\/span><\/span>\n\/\/  ReverseCompare.h<\/span><\/span>\n\/\/  Function Overload Resolution<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 10\/14\/24.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#ifndef<\/span> ReverseCompare_h<\/span><\/span>\n#define<\/span> ReverseCompare_h<\/span><\/span>\n<\/span>\nclass<\/span> <\/span>ReverseCompare<\/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>  \/\/ reverse compare<\/span><\/span>\n  }<\/span><\/span>\n};<\/span><\/span>\n<\/span>\n#endif<\/span> \/* ReverseCompare_h *\/<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n\n\n\n
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\/\/<\/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>"ReverseCompare.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> *>(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><\/span>\n  <\/span>sort<\/span><<\/span>const<\/span> <\/span>char<\/span> *, <\/span>ReverseCompare<\/span>>(vstrs);<\/span><\/span>\n    <\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>"After reverse 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<\/div>\n\n\n\n
Which produces the following output:<\/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\nAfter reverse 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\n\n\n
<\/div>\n\n\n\n
\n
Next: Template Value Parameter Usage<\/a><\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"
Default Template Parameters Rather than force you always to specify the Comp class explicitly, it would be nice to be able to default it to the most common case. You can do this by supplying two function templates: More conveniently, you can use default template parameters: So, with some minor changes to a couple of […]<\/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-2070","page","type-page","status-publish","hentry"],"blocksy_meta":[],"_links":{"self":[{"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/pages\/2070","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=2070"}],"version-history":[{"count":4,"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/pages\/2070\/revisions"}],"predecessor-version":[{"id":2099,"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/pages\/2070\/revisions\/2099"}],"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=2070"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}