{"id":216,"date":"2019-09-02T00:56:36","date_gmt":"2019-09-01T16:56:36","guid":{"rendered":"http:\/\/www.eolstudy.com\/?p=216"},"modified":"2019-09-07T02:49:35","modified_gmt":"2019-09-06T18:49:35","slug":"c-%e9%bb%98%e8%ae%a4%e5%8f%82%e6%95%b0%e6%b3%a8%e6%84%8f%e4%ba%8b%e9%a1%b9%e6%80%bb%e7%bb%93","status":"publish","type":"post","link":"https:\/\/www.eolstudy.com\/index.php\/2019\/09\/study-notes\/cpp\/216\/","title":{"rendered":"C++ \u9ed8\u8ba4\u53c2\u6570\u6ce8\u610f\u4e8b\u9879\u603b\u7ed3"},"content":{"rendered":"\n<h2 class=\"wp-block-heading\">\u91cd\u590d\u58f0\u660e<\/h2>\n\n\n\n<p>\u4e0d\u542b\u9ed8\u8ba4\u53c2\u6570\u7684\u51fd\u6570\u53ef\u4ee5\u91cd\u590d\u591a\u6b21\u58f0\u660e\uff0c\u800c\u542b\u6709\u9ed8\u8ba4\u53c2\u6570\u7684\u51fd\u6570\u5728\u91cd\u590d\u58f0\u660e\u65f6\uff1a<\/p>\n\n\n\n<div class=\"wp-block-jetpack-markdown\"><ul>\n<li>\u9ed8\u8ba4\u53c2\u6570\u7684\u9ed8\u8ba4\u503c\u4e0d\u80fd\u91cd\u590d\u58f0\u660e\u3002<\/li>\n<li>\u9ed8\u8ba4\u53c2\u6570\u7684\u9ed8\u8ba4\u503c\u540c\u6837\u4e5f\u4e0d\u80fd\u4fee\u6539\u3002<\/li>\n<\/ul>\n<\/div>\n\n\n\n<h2 class=\"wp-block-heading\">\u8ffd\u52a0\u9ed8\u8ba4\u53c2\u6570<\/h2>\n\n\n\n<p>\u975e\u9ed8\u8ba4\u53c2\u6570\u5728\u540e\u7eed\u58f0\u660e\u65f6\u53ef\u8ffd\u52a0\u9ed8\u8ba4\u503c\uff0c\u4f46\u9700\u4fdd\u8bc1\u8ffd\u52a0\u7684 n \u4e2a\u65b0\u9ed8\u8ba4\u53c2\u6570\u540c\u6837\u662f\u539f\u975e\u9ed8\u8ba4\u53c2\u6570\u4e2d\u7684\u6700\u540e n \u4e2a\u3002\u8003\u8651\u5230 #\u91cd\u590d\u58f0\u660e \u4e2d\u63d0\u5230\u7684\u8981\u6c42\uff0c\u5df2\u5b58\u5728\u9ed8\u8ba4\u503c\u7684\u53c2\u6570\u4e0d\u80fd\u518d\u6b21\u58f0\u660e\u9ed8\u8ba4\u503c\u3002<\/p>\n\n\n\n<p>\u4f8b\u5982\uff0c\u6709\u4ee5\u4e0b\u51fd\u6570\u58f0\u660e\uff1a<\/p>\n\n\n\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"cpp\" data-enlighter-theme=\"\" data-enlighter-highlight=\"\" data-enlighter-linenumbers=\"false\" data-enlighter-lineoffset=\"\" data-enlighter-title=\"\" data-enlighter-group=\"\">void f(int a, int b, int c, int d = 0);<\/pre>\n\n\n\n<p>\u82e5\u8981\u4e3a\u5176\u4e2d\u7684\u53c2\u6570 <code>b<\/code>\u3001<code>c<\/code> \u8ffd\u52a0\u9ed8\u8ba4\u503c\u65f6\uff0c\u53ef\u4ee5\u4ee5\u5982\u4e0b\u5f62\u5f0f\uff1a<\/p>\n\n\n\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"cpp\" data-enlighter-theme=\"\" data-enlighter-highlight=\"\" data-enlighter-linenumbers=\"false\" data-enlighter-lineoffset=\"\" data-enlighter-title=\"\" data-enlighter-group=\"\">void f(int a, int b = 2, int c = 1, int d);<\/pre>\n\n\n\n<p>\u8ffd\u52a0\u9ed8\u8ba4\u53c2\u6570\u7684\u7279\u6027\u9002\u5408\u7528\u4e8e\u4e0d\u540c\u6587\u4ef6\u4e2d\u76f8\u540c\u53c2\u6570\u51fa\u73b0\u4e0d\u540c\u9ad8\u9891\u521d\u59cb\u503c\u7684\u60c5\u51b5\u3002<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">\u9ed8\u8ba4\u503c\u65e0\u9700\u7f16\u8bd1\u65f6\u786e\u5b9a<\/h2>\n\n\n\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"cpp\" data-enlighter-theme=\"\" data-enlighter-highlight=\"\" data-enlighter-linenumbers=\"\" data-enlighter-lineoffset=\"\" data-enlighter-title=\"\" data-enlighter-group=\"\">int rand_gen()\n{\n    return rand() % 10;\n}\n\nvoid foo(int a = rand_gen());<\/pre>\n\n\n\n<p>\u4ee5\u4e0a\u9ed8\u8ba4\u53c2\u6570\u7684\u58f0\u660e\u662f\u5b8c\u5168\u6b63\u786e\u7684\u3002\u8c03\u7528 <code>foo()<\/code> \u65f6\uff0c\u7a0b\u5e8f\u4f1a\u5148\u6267\u884c rand_gen()\uff0c\u5e76\u4ee5\u8fd4\u56de\u503c\u521d\u59cb\u5316\u53c2\u6570 <code>a<\/code>\u3002<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">\u9ed8\u8ba4\u503c\u4e0d\u5f97\u4f9d\u8d56\u5f62\u53c2\u5217\u8868\u4e2d\u5176\u4ed6\u53c2\u6570<\/h2>\n\n\n\n<p>\u58f0\u660e\u9ed8\u8ba4\u53c2\u6570\u65f6\uff0c\u9ed8\u8ba4\u53c2\u6570\u7684\u503c\u867d\u7136\u65e0\u9700\u7f16\u8bd1\u65f6\u786e\u5b9a\uff0c\u4f46\u4ecd\u9700\u8981\u4fdd\u8bc1\u4e0d\u4f9d\u8d56\u5176\u4ed6\u9ed8\u8ba4\u53c2\u6570\u3002<\/p>\n\n\n\n<p>\u4f8b\u5982\uff0c\u4ee5\u4e0b\u4ee3\u7801<\/p>\n\n\n\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"cpp\" data-enlighter-theme=\"\" data-enlighter-highlight=\"\" data-enlighter-linenumbers=\"\" data-enlighter-lineoffset=\"\" data-enlighter-title=\"\" data-enlighter-group=\"\">int g(int);\nvoid foo(int a = b, int b = 0);\nvoid bar(int a = 0, int b = g(a));<\/pre>\n\n\n\n<p>\u4e0a\u8ff0\u793a\u4f8b\u4e2d\uff0cgcc(7.4.0) \u4e0e clang(6.0.0) \u5bf9 <code>foo<\/code> \u51fd\u6570\u4e0e <code>bar<\/code> \u51fd\u6570\u7684\u58f0\u660e\u5747\u62a5 <code>error<\/code>\u3002\u5176\u4e2d\u5bf9 <code>foo<\/code> \u58f0\u660e\u7684\u62a5\u9519\u4fe1\u606f\u5747\u662f\u6307\u51fa <code>a<\/code> \u58f0\u660e\u65f6 <code>b<\/code> \u5c1a\u672a\u58f0\u660e\uff0c\u800c\u5bf9 <code>bar<\/code> \u51fd\u6570\u58f0\u660e\u7684\u62a5\u9519\u5219\u4e0d\u76f8\u540c\uff08\u53ef\u81ea\u884c\u5b9e\u9a8c\uff09\u3002<\/p>\n\n\n\n<p>\u4e8b\u5b9e\u4e0a\uff0cC++ \u6807\u51c6\uff08\u622a\u81f3 C++ 17\uff09\u5e76\u672a\u89c4\u5b9a\u51fd\u6570\u53c2\u6570\u7684\u521d\u59cb\u5316\u987a\u5e8f\uff0c\u56e0\u6b64\uff0c<code>foo<\/code> \u6216 <code>bar<\/code> \u4e2d\u7684\u4e24\u4e2a\u53c2\u6570\u4f55\u8005\u5148\u521d\u59cb\u5316\u4f9d\u8d56\u7f16\u8bd1\u5668\u5b9e\u73b0\uff0c\u81ea\u7136\u4e0d\u80fd\u591f\u5141\u8bb8\u5176\u95f4\u51fa\u73b0\u4f9d\u8d56\u5173\u7cfb\u3002<s class=\"has-cyan-bluish-gray-color\" style=\"font-size: small\">\u660e\u660e\u53ea\u8981\u89c4\u5b9a\u4e00\u4e0b\u5c31\u5b8c\u5168\u6ca1\u6709\u95ee\u9898\u7684 _(\u2022\u0300\u03c9\u2022\u0301 \u300d\u2220)_<\/s><\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\"><p>Default arguments are evaluated each time the function is called. The order of evaluation of function arguments is unspecified. Consequently, parameters of a function shall not be used in default argument expressions, even if they are not evaluated.<\/p><cite>\u00a78.3.6\/9, ISO\/IEC 14882:2003<\/cite><\/blockquote>\n\n\n\n<p><strong>\u7279\u522b\u5730<\/strong>\uff0c\u5f53\u542b\u6709\u9ed8\u8ba4\u53c2\u6570\u7684\u51fd\u6570\u4e3a\u6210\u5458\u51fd\u6570\u65f6\uff0c\u6781\u6613\u72af\u7c7b\u4f3c\u95ee\u9898\uff1a<\/p>\n\n\n\n<p class=\"has-text-color has-small-font-size has-cyan-bluish-gray-color\"><s>\uff08\u6211\u4e0d\u4f1a\u8bf4\u8fd9\u662f\u56e0\u4e3a\u6211\u9519\u8fc7\u4e24\u6b21\uff09<\/s><\/p>\n\n\n\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"cpp\" data-enlighter-theme=\"\" data-enlighter-highlight=\"\" data-enlighter-linenumbers=\"\" data-enlighter-lineoffset=\"\" data-enlighter-title=\"\" data-enlighter-group=\"\">struct X\n{\n    X():mem(42){}\n    void f(int param = mem) \/\/ERROR\n    {\n        \/\/do something\n    }\nprivate: \n    int mem;\n};<\/pre>\n\n\n\n<p>\u6210\u5458\u51fd\u6570\u5b9e\u9645\u7684\u53c2\u6570\u6bd4\u58f0\u660e\u4e2d\u591a\u4e00\u4e2a <code>this<\/code> \u6307\u9488\u3002\u56e0\u6b64\uff0c\u770b\u4f3c\u53ea\u6709\u4e00\u4e2a\u53c2\u6570\u7684 <code>X::f<\/code> \u4e8b\u5b9e\u4e0a\u7684\u539f\u578b\u4e3a<\/p>\n\n\n\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"cpp\" data-enlighter-theme=\"\" data-enlighter-highlight=\"\" data-enlighter-linenumbers=\"false\" data-enlighter-lineoffset=\"\" data-enlighter-title=\"\" data-enlighter-group=\"\">void f(X* this, int param = this->mem);<\/pre>\n\n\n\n<p>\u56e0\u6b64 <code>param<\/code> \u53c2\u6570\u548c\u7b2c\u4e00\u4e2a\u53c2\u6570 <code>this<\/code> \u4fbf\u51fa\u73b0\u4e86\u4f9d\u8d56\u5173\u7cfb\u3002<\/p>\n\n\n\n<p>\u53c2\u8003\u94fe\u63a5\uff1a<a href=\"https:\/\/stackoverflow.com\/questions\/4539406\/nonstatic-member-as-a-default-argument-of-a-nonstatic-member-function\">https:\/\/stackoverflow.com\/questions\/4539406\/nonstatic-member-as-a-default-argument-of-a-nonstatic-member-function<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u91cd\u590d\u58f0\u660e \u4e0d\u542b\u9ed8\u8ba4\u53c2\u6570\u7684\u51fd\u6570\u53ef\u4ee5\u91cd\u590d\u591a\u6b21\u58f0\u660e\uff0c\u800c\u542b\u6709\u9ed8\u8ba4\u53c2\u6570\u7684\u51fd\u6570\u5728\u91cd\u590d\u58f0\u660e\u65f6\uff1a \u8ffd\u52a0\u9ed8\u8ba4\u53c2\u6570 \u975e\u9ed8\u8ba4\u53c2\u6570\u5728\u540e\u7eed\u58f0\u660e\u65f6\u53ef\u8ffd\u52a0\u9ed8\u8ba4\u503c\uff0c\u4f46\u9700\u4fdd\u8bc1\u8ffd\u52a0\u7684 n \u4e2a\u65b0\u9ed8\u8ba4\u53c2\u6570\u540c\u6837\u662f\u539f\u975e\u9ed8\u8ba4\u53c2\u6570\u4e2d\u7684\u6700\u540e n \u4e2a\u3002\u8003\u8651\u5230 #\u91cd\u590d\u58f0\u660e \u4e2d\u63d0\u5230\u7684\u8981\u6c42\uff0c\u5df2\u5b58\u5728\u9ed8\u8ba4\u503c\u7684\u53c2\u6570\u4e0d\u80fd\u518d\u6b21\u58f0\u660e\u9ed8\u8ba4\u503c\u3002 \u4f8b\u5982\uff0c\u6709\u4ee5\u4e0b\u51fd\u6570\u58f0\u660e\uff1a \u82e5\u8981\u4e3a\u5176\u4e2d\u7684\u53c2\u6570 b\u3001c \u8ffd\u52a0\u9ed8\u8ba4\u503c\u65f6\uff0c\u53ef\u4ee5\u4ee5\u5982\u4e0b\u5f62\u5f0f\uff1a \u8ffd\u52a0\u9ed8\u8ba4\u53c2\u6570\u7684\u7279\u6027\u9002\u5408\u7528\u4e8e\u4e0d\u540c\u6587\u4ef6\u4e2d\u76f8\u540c\u53c2\u6570\u51fa\u73b0\u4e0d\u540c\u9ad8\u9891\u521d\u59cb\u503c\u7684\u60c5\u51b5\u3002 \u9ed8\u8ba4\u503c\u65e0\u9700\u7f16\u8bd1\u65f6\u786e\u5b9a \u4ee5\u4e0a\u9ed8\u8ba4\u53c2\u6570\u7684\u58f0\u660e\u662f\u5b8c\u5168\u6b63\u786e\u7684\u3002\u8c03\u7528 foo() \u65f6\uff0c\u7a0b\u5e8f\u4f1a\u5148\u6267\u884c rand_gen()\uff0c\u5e76\u4ee5\u8fd4\u56de\u503c\u521d\u59cb\u5316\u53c2\u6570 a\u3002 \u9ed8\u8ba4\u503c\u4e0d\u5f97\u4f9d\u8d56\u5f62\u53c2\u5217\u8868\u4e2d\u5176\u4ed6\u53c2\u6570 \u58f0\u660e\u9ed8\u8ba4\u53c2\u6570\u65f6\uff0c\u9ed8\u8ba4\u53c2\u6570\u7684\u503c\u867d\u7136\u65e0\u9700\u7f16\u8bd1\u65f6\u786e\u5b9a\uff0c\u4f46\u4ecd\u9700\u8981\u4fdd\u8bc1\u4e0d\u4f9d\u8d56\u5176\u4ed6\u9ed8\u8ba4\u53c2\u6570\u3002 \u4f8b\u5982\uff0c\u4ee5\u4e0b\u4ee3\u7801 \u4e0a\u8ff0\u793a\u4f8b\u4e2d\uff0cgcc(7.4.0) \u4e0e clang(6.0.0) \u5bf9 foo \u51fd\u6570\u4e0e bar \u51fd\u6570\u7684\u58f0\u660e\u5747\u62a5 error\u3002\u5176\u4e2d\u5bf9 foo \u58f0\u660e\u7684\u62a5\u9519\u4fe1\u606f\u5747\u662f\u6307\u51fa a \u58f0\u660e\u65f6 b \u5c1a\u672a\u58f0\u660e\uff0c\u800c\u5bf9 bar \u51fd\u6570\u58f0\u660e\u7684\u62a5\u9519\u5219\u4e0d\u76f8\u540c\uff08\u53ef\u81ea\u884c\u5b9e\u9a8c\uff09\u3002 \u4e8b\u5b9e\u4e0a\uff0cC++ \u6807\u51c6\uff08\u622a\u81f3 C++ 17\uff09\u5e76\u672a\u89c4\u5b9a\u51fd\u6570\u53c2\u6570\u7684\u521d\u59cb\u5316\u987a\u5e8f\uff0c\u56e0\u6b64\uff0cfoo \u6216 bar \u4e2d\u7684\u4e24\u4e2a\u53c2\u6570\u4f55\u8005\u5148\u521d\u59cb\u5316\u4f9d\u8d56\u7f16\u8bd1\u5668\u5b9e\u73b0\uff0c\u81ea\u7136\u4e0d\u80fd\u591f\u5141\u8bb8\u5176\u95f4\u51fa\u73b0\u4f9d\u8d56\u5173\u7cfb\u3002\u660e\u660e\u53ea\u8981\u89c4\u5b9a\u4e00\u4e0b\u5c31\u5b8c\u5168\u6ca1\u6709\u95ee\u9898\u7684 _(\u2022\u0300\u03c9\u2022\u0301 \u300d\u2220)_ Default arguments are evaluated each [&hellip;]<\/p>\n","protected":false},"author":2,"featured_media":259,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","enabled":false},"version":2}},"categories":[14,17],"tags":[15,16],"class_list":["post-216","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-cpp","category-recommendation","tag-c","tag-16"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"https:\/\/www.eolstudy.com\/wp-content\/uploads\/2019\/09\/sumita-arora-c-plus-plus-pdf-download.jpg","jetpack_sharing_enabled":true,"jetpack_likes_enabled":true,"_links":{"self":[{"href":"https:\/\/www.eolstudy.com\/index.php\/wp-json\/wp\/v2\/posts\/216"}],"collection":[{"href":"https:\/\/www.eolstudy.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.eolstudy.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.eolstudy.com\/index.php\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.eolstudy.com\/index.php\/wp-json\/wp\/v2\/comments?post=216"}],"version-history":[{"count":6,"href":"https:\/\/www.eolstudy.com\/index.php\/wp-json\/wp\/v2\/posts\/216\/revisions"}],"predecessor-version":[{"id":260,"href":"https:\/\/www.eolstudy.com\/index.php\/wp-json\/wp\/v2\/posts\/216\/revisions\/260"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.eolstudy.com\/index.php\/wp-json\/wp\/v2\/media\/259"}],"wp:attachment":[{"href":"https:\/\/www.eolstudy.com\/index.php\/wp-json\/wp\/v2\/media?parent=216"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.eolstudy.com\/index.php\/wp-json\/wp\/v2\/categories?post=216"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.eolstudy.com\/index.php\/wp-json\/wp\/v2\/tags?post=216"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}