{"id":25255,"date":"2022-12-09T01:10:20","date_gmt":"2022-12-08T19:40:20","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-why-can-not-use-return-lhs-size-rhs-size-in-stdsort-compare-function\/"},"modified":"2022-12-09T01:10:20","modified_gmt":"2022-12-08T19:40:20","slug":"solved-why-can-not-use-return-lhs-size-rhs-size-in-stdsort-compare-function","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-why-can-not-use-return-lhs-size-rhs-size-in-stdsort-compare-function\/","title":{"rendered":"[Solved] Why can not use “return lhs.size() == rhs.size()” in std::sort() compare function?"},"content":{"rendered":"

[ad_1]
\n<\/p>\n

\n
\n
<\/div>\n
\n
\n

Because comp1(a,b)<\/code> and comp1(b,a)<\/code> can both return true<\/code>, which isn’t allowed. std::sort<\/code><\/a> states that:<\/p>\n

\n

comp – comparison function object (i.e. an object that satisfies the requirements of Compare<\/a>) which returns \u200btrue if the first argument is less than (i.e. is ordered before) the second. <\/p>\n<\/blockquote>\n

And following the link to Compare<\/a> we also see:<\/p>\n

\n

Establishes strict weak ordering<\/a> relation with the following properties
\n * For all a, comp(a,a)==false
\n * If comp(a,b)==true then comp(b,a)==false
\n * if comp(a,b)==true and comp(b,c)==true then comp(a,c)==true<\/p>\n<\/blockquote>\n

Your first function, comp<\/code>, satisfies those requirements: no two objects could return true<\/code>. If comp(a,b)<\/code> returns true,<\/code> then comp(b,a)<\/code> returns false<\/code>; however, this is not the case in your second function, comp1<\/code>. comp1(a,b)<\/code> can return true<\/code>, as can comp(b,a)<\/code>, so sort<\/code> will never finish and therefore it won’t compile.<\/p>\n

You state that<\/p>\n

\n

i want to put those same size strings together<\/p>\n<\/blockquote>\n

But just using operator<<\/code> will achieve those results: any string the same size will be grouped together.<\/p>\n<\/p><\/div>\n

<\/div>\n<\/div>\n

1<\/span> <\/p><\/div>\n<\/div>\n

[ad_2]<\/p>\n

solved Why can not use “return lhs.size() == rhs.size()” in std::sort() compare function? <\/p>\n","protected":false},"excerpt":{"rendered":"

[ad_1] Because comp1(a,b) and comp1(b,a) can both return true, which isn’t allowed. std::sort states that: comp – comparison function object (i.e. an object that satisfies the requirements of Compare) which returns \u200btrue if the first argument is less than (i.e. is ordered before) the second. And following the link to Compare we also see: Establishes … Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[320],"tags":[324],"class_list":["post-25255","post","type-post","status-publish","format-standard","hentry","category-solved","tag-c"],"yoast_head":"\n[Solved] Why can not use "return lhs.size() == rhs.size()" in std::sort() compare function? - JassWeb<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/jassweb.com\/solved\/solved-why-can-not-use-return-lhs-size-rhs-size-in-stdsort-compare-function\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"[Solved] Why can not use "return lhs.size() == rhs.size()" in std::sort() compare function? - JassWeb\" \/>\n<meta property=\"og:description\" content=\"[ad_1] Because comp1(a,b) and comp1(b,a) can both return true, which isn’t allowed. std::sort states that: comp – comparison function object (i.e. an object that satisfies the requirements of Compare) which returns \u200btrue if the first argument is less than (i.e. is ordered before) the second. And following the link to Compare we also see: Establishes ... 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