{"id":367,"date":"2020-11-03T12:17:34","date_gmt":"2020-11-03T16:17:34","guid":{"rendered":"http:\/\/www.prglab.com\/blog\/?page_id=367"},"modified":"2020-11-03T12:17:34","modified_gmt":"2020-11-03T16:17:34","slug":"namespaces","status":"publish","type":"page","link":"https:\/\/www.prglab.com\/blog\/cplusplus-tutorial\/advanced-concepts\/namespaces","title":{"rendered":"\u547d\u540d\u7a7a\u95f4"},"content":{"rendered":"\n<h2>5.2 \u547d\u540d\u7a7a\u95f4 (Namespaces)<\/h2>\n\n\n\n<p>\u901a\u8fc7\u4f7f\u7528\u547d\u540d\u7a7a\u95f4(Namespaces)\u6211\u4eec\u53ef\u4ee5\u5c06\u4e00\u7ec4\u5168\u5c40\u8303\u56f4\u6709\u6548\u7684\u7c7b\u3001\u5bf9\u8c61\u6216\u51fd\u6570\u7ec4\u7ec7\u5230\u4e00\u4e2a\u540d\u5b57\u4e0b\u9762\u3002\u6362\u79cd\u8bf4\u6cd5\uff0c\u5c31\u662f\u5b83\u5c06\u5168\u5c40\u8303\u56f4\u5206\u5272\u6210\u8bb8\u591a\u5b50\u57df\u8303\u56f4\uff0c\u6bcf\u4e2a\u5b50\u57df\u8303\u56f4\u53eb\u505a\u4e00\u4e2a\u547d\u540d\u7a7a\u95f4(namespaces).<\/p>\n\n\n\n<p>\u4f7f\u7528\u547d\u540d\u7a7a\u95f4\u7684\u683c\u5f0f\u662f\uff1a<\/p>\n\n\n\n<pre class=\"wp-block-preformatted\">\tnamespace identifier<br>\t{<br>\t    namespace-body<br>\t}<\/pre>\n\n\n\n<p>\u8fd9\u91ccidentifier \u662f\u4e00\u4e2a\u6709\u6548\u7684\u6807\u793a\u7b26\uff0cnamespace-body \u662f\u8be5\u547d\u540d\u7a7a\u95f4\u5305\u542b\u7684\u4e00\u7ec4\u7c7b\u3001\u5bf9\u8c61\u548c\u51fd\u6570\u3002\u4f8b\u5982\uff1a<\/p>\n\n\n\n<pre class=\"wp-block-preformatted\">\tnamespace general<br>\t{<br>\t    int a, b;<br>\t}<\/pre>\n\n\n\n<p>\u5728\u8fd9\u4e2a\u4f8b\u5b50\u4e2d\uff0ca \u548c b \u662f\u547d\u540d\u7a7a\u95f4general\u4e2d\u7684\u6574\u578b\u53d8\u91cf\u3002\u8981\u60f3\u5728\u8fd9\u4e2a\u540d\u7a7a\u95f4\u5916\u9762\u8bbf\u95ee\u8fd9\u4e24\u4e2a\u53d8\u91cf\uff0c\u6211\u4eec\u5fc5\u987b\u4f7f\u7528\u8303\u56f4\u64cd\u4f5c\u7b26::\u3002\u4f8b\u5982\uff0c\u8981\u60f3\u8bbf\u95ee\u524d\u9762\u7684\u4e24\u4e2a\u53d8\u91cf\uff0c\u6211\u4eec\u9700\u8981\u8fd9\u6837\u5199\uff1a<\/p>\n\n\n\n<p><code>general::a<br>general::b<\/code><\/p>\n\n\n\n<p>\u547d\u540d\u7a7a\u95f4(namespaces)\u7684\u4f5c\u7528\u5728\u4e8e\u5168\u5c40\u5bf9\u8c61\u6216\u51fd\u6570\u5f88\u6709\u53ef\u80fd\u91cd\u540d\u800c\u9020\u6210\u91cd\u590d\u5b9a\u4e49\u7684\u9519\u8bef\uff0c\u547d\u540d\u7a7a\u95f4\u7684\u4f7f\u7528\u53ef\u4ee5\u907f\u514d\u8fd9\u4e9b\u9519\u8bef\u7684\u53d1\u751f\u3002\u4f8b\u5982\uff1a<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table><tbody><tr><td>\/\/ namespaces #include &lt;iostream.h&gt; namespace first { int var = 5; } namespace second { double var = 3.1416; } int main () { cout &lt;&lt; first::var &lt;&lt; endl; cout &lt;&lt; second::var &lt;&lt; endl; return 0; }<\/td><td>5<br>3.1416<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p>\u5728\u8fd9\u4e2a\u4f8b\u5b50\u4e2d\uff0c\u4e24\u4e2a\u90fd\u53eb\u505avar\u5168\u5c40\u53d8\u91cf\u540c\u65f6\u5b58\u5728\uff0c\u4e00\u4e2a\u5728\u547d\u540d\u7a7a\u95f4first \u4e0b\u9762\u5b9a\u4e49\uff0c\u53e6\u4e00\u4e2a\u5728 second\u4e0b\u9762\u5b9a\u4e49\uff0c\u7531\u4e8e\u6211\u4eec\u4f7f\u7528\u4e86\u547d\u540d\u7a7a\u95f4\uff0c\u8fd9\u91cc\u4e0d\u4f1a\u4ea7\u751f\u91cd\u590d\u5b9a\u4e49\u7684\u9519\u8bef\u3002<\/p>\n\n\n\n<h3>\u547d\u540d\u7a7a\u95f4\u7684\u4f7f\u7528 (using namespace)<\/h3>\n\n\n\n<p>\u4f7f\u7528 using \u6307\u4ee4\u540e\u9762\u8ddfnamespace\u53ef\u4ee5\u5c06\u5f53\u524d\u7684\u5d4c\u5957\u5c42\u4e0e\u4e00\u4e2a\u6307\u5b9a\u7684\u547d\u540d\u7a7a\u95f4\u8fde\u5728\u4e00\u8d77\uff0c\u4ee5\u4fbf\u4f7f\u8be5\u547d\u540d\u7a7a\u95f4\u4e0b\u5b9a\u4e49\u7684\u5bf9\u8c61\u548c\u51fd\u6570\u53ef\u4ee5\u88ab\u8bbf\u95ee\uff0c\u5c31\u597d\u50cf\u5b83\u4eec\u662f\u5728\u5168\u5c40\u8303\u56f4\u5185\u88ab\u5b9a\u4e49\u7684\u4e00\u6837\u3002\u5b83\u7684\u4f7f\u7528\u9075\u5faa\u4ee5\u4e0b\u539f\u578b\u5b9a\u4e49\uff1a<code>using namespace identifier;<\/code><\/p>\n\n\n\n<p>\u4f8b\u5982\uff1a<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table><tbody><tr><td>\/\/ using namespace example #include &lt;iostream.h&gt; namespace first { int var = 5; } namespace second { double var = 3.1416; } int main () { using namespace second; cout &lt;&lt; var &lt;&lt; endl; cout &lt;&lt; (var*2) &lt;&lt; endl; return 0; }<\/td><td>3.1416<br>6.2832<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p>\u5728\u8fd9\u4e2a\u4f8b\u5b50\u4e2d\u7684main\u51fd\u6570\u4e2d\u53ef\u4ee5\u770b\u5230\uff0c\u6211\u4eec\u80fd\u591f\u76f4\u63a5\u4f7f\u7528\u53d8\u91cfvar \u800c\u4e0d\u7528\u5728\u524d\u9762\u52a0\u4efb\u4f55\u8303\u56f4\u64cd\u4f5c\u7b26\u3002<\/p>\n\n\n\n<p>\u8fd9\u91cc\u8981\u6ce8\u610f\uff0c\u8bed\u53e5using namespace \u53ea\u5728\u5176\u88ab\u58f0\u660e\u7684\u8bed\u53e5\u5757\u5185\u6709\u6548\uff08\u4e00\u4e2a\u8bed\u53e5\u5757\u6307\u5728\u4e00\u5bf9\u82b1\u62ec\u53f7{}\u5185\u7684\u4e00\u7ec4\u6307\u4ee4)\uff0c\u5982\u679cusing namespace\u662f\u5728\u5168\u5c40\u8303\u56f4\u5185\u88ab\u58f0\u660e\u7684\uff0c\u5219\u5728\u6240\u6709\u4ee3\u7801\u4e2d\u90fd\u6709\u6548\u3002\u4f8b\u5982\uff0c\u5982\u679c\u6211\u4eec\u60f3\u5728\u4e00\u6bb5\u7a0b\u5e8f\u4e2d\u4f7f\u7528\u4e00\u4e2a\u547d\u540d\u7a7a\u95f4\uff0c\u800c\u5728\u53e6\u4e00\u6bb5\u7a0b\u5e8f\u4e2d\u4f7f\u7528\u53e6\u4e00\u4e2a\u547d\u540d\u7a7a\u95f4\uff0c\u5219\u53ef\u4ee5\u50cf\u4ee5\u4e0b\u4ee3\u7801\u4e2d\u90a3\u6837\u505a\uff1a<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table><tbody><tr><td>\/\/ using namespace example #include &lt;iostream.h&gt; namespace first { int var = 5; } namespace second { double var = 3.1416; } int main () { {<br>using namespace first; cout &lt;&lt; var &lt;&lt; endl; }<br>{<br>using namespace second; cout &lt;&lt; var &lt;&lt; endl; } return 0; }<\/td><td>5<br>3.1416<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<h3>\u522b\u540d\u5b9a\u4e49(alias definition)<\/h3>\n\n\n\n<p>\u6211\u4eec\u4ee5\u53ef\u4ee5\u4e3a\u5df2\u7ecf\u5b58\u5728\u7684\u547d\u540d\u7a7a\u95f4\u5b9a\u4e49\u522b\u540d\uff0c\u683c\u5f0f\u4e3a\uff1a<code>namespace new_name = current_name ;<\/code><\/p>\n\n\n\n<h3>\u6807\u51c6\u547d\u540d\u7a7a\u95f4(Namespace std)<\/h3>\n\n\n\n<p>\u6211\u4eec\u80fd\u591f\u627e\u5230\u7684\u5173\u4e8e\u547d\u540d\u7a7a\u95f4\u7684\u6700\u597d\u7684\u4f8b\u5b50\u5c31\u662f\u6807\u51c6C++ \u51fd\u6570\u5e93\u672c\u8eab\u3002\u5982ANSI C++ \u6807\u51c6\u5b9a\u4e49\uff0c\u6807\u51c6C++\u5e93\u4e2d\u7684\u6240\u6709\u7c7b\u3001\u5bf9\u8c61\u548c\u51fd\u6570\u90fd\u662f\u5b9a\u4e49\u5728\u547d\u540d\u7a7a\u95f4std\u4e0b\u9762\u7684\u3002<\/p>\n\n\n\n<p>\u4f60\u53ef\u80fd\u5df2\u7ecf\u6ce8\u610f\u5230\uff0c\u6211\u4eec\u5728\u8fd9\u4e2a\u6559\u7a0b\u4e2d\u5168\u90e8\u5ffd\u7565\u4e86\u8fd9\u4e00\u70b9\u3002\u4f5c\u8005\u51b3\u5b9a\u8fd9\u4e48\u505a\u662f\u56e0\u4e3a\u8fd9\u6761\u89c4\u5219\u51e0\u4e4e\u548cANSI \u6807\u51c6\u672c\u8eab\u4e00\u6837\u5e74\u8f7b (1997) \uff0c\u8bb8\u591a\u8001\u4e00\u70b9\u7684\u7f16\u8bd1\u5668\u5e76\u4e0d\u517c\u5bb9\u8fd9\u6761\u89c4\u5219\u3002<\/p>\n\n\n\n<p>\u51e0\u4e4e\u6240\u6709\u7684\u7f16\u8bd1\u5668\uff0c\u5373\u4f7f\u662f\u90a3\u4e9b\u4e0eANSI \u6807\u51c6\u517c\u5bb9\u7684\u7f16\u8bd1\u5668\uff0c\u90fd\u5141\u8bb8\u4f7f\u7528\u4f20\u7edf\u7684\u5934\u6587\u4ef6 (\u5982iostream.h, stdlib.h, \u7b49\u7b49)\uff0c\u5c31\u50cf\u6211\u4eec\u5728\u8fd9\u4e2a\u6559\u7a0b\u4e2d\u6240\u4f7f\u7528\u7684\u4e00\u6837\u3002\u7136\u800c\uff0cANSI\u6807\u51c6\u5b8c\u5168\u91cd\u65b0\u8bbe\u8ba1\u4e86\u8fd9\u4e9b\u51fd\u6570\u5e93\uff0c\u5229\u7528\u4e86\u6a21\u677f\u529f\u80fd\uff0c\u800c\u4e14\u9075\u5faa\u4e86\u8fd9\u6761\u89c4\u5219\u5c06\u6240\u6709\u7684\u51fd\u6570\u548c\u53d8\u91cf\u5b9a\u4e49\u5728\u4e86\u547d\u540d\u7a7a\u95f4std\u4e0b\u3002<\/p>\n\n\n\n<p>\u8be5\u6807\u51c6\u4e3a\u8fd9\u4e9b\u5934\u6587\u4ef6\u5b9a\u4e49\u4e86\u65b0\u7684\u540d\u5b57\uff0c\u5bf9\u9488\u5bf9C++\u7684\u6587\u4ef6\u57fa\u672c\u4e0a\u662f\u4f7f\u7528\u540c\u6837\u7684\u540d\u5b57\uff0c\u4f46\u6ca1\u6709.h\u7684\u6269\u5c55\u540d\uff0c\u4f8b\u5982, iostream.h \u53d8\u6210\u4e86iostream\u3002<\/p>\n\n\n\n<p>\u5982\u679c\u6211\u4eec\u4f7f\u7528ANSI-C++ \u517c\u5bb9\u7684\u5305\u542b\u6587\u4ef6\uff0c\u6211\u4eec\u5fc5\u987b\u8bb0\u4f4f\u6240\u6709\u7684\u51fd\u6570\u3001\u7c7b\u548c\u5bf9\u8c61\u662f\u5b9a\u4e49\u5728\u547d\u540d\u7a7a\u95f4 std \u4e0b\u9762\u7684\uff0c\u4f8b\u5982\uff1a<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table><tbody><tr><td>\/\/ ANSI-C++ compliant hello world #include &lt;iostream&gt; int main () { std::cout &lt;&lt; &#8220;Hello world in ANSI-C++\\n&#8221;;<br>return 0;<br>}<br><\/td><td>Hello world in ANSI-C++<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p>\u66f4\u5e38\u7528\u7684\u65b9\u6cd5\u662f\u4f7f\u7528using namespace \uff0c\u8fd9\u6837\u6211\u4eec\u5c31\u4e0d\u5fc5\u5728\u6240\u6709\u6807\u51c6\u7a7a\u95f4\u4e2d\u5b9a\u4e49\u7684\u51fd\u6570\u6216\u5bf9\u8c61\u524d\u9762\u603b\u662f\u4f7f\u7528\u8303\u56f4\u64cd\u4f5c\u7b26::\u4e86 \uff1a<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table><tbody><tr><td>\/\/ ANSI-C++ compliant hello world (II) #include &lt;iostream&gt; using namespace std; int main () { cout &lt;&lt; &#8220;Hello world in ANSI-C++\\n&#8221;; return 0; }<\/td><td>Hello world in ANSI-C++<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p>\u5bf9\u4e8eSTL \u7528\u6237\uff0c\u5f3a\u70c8\u5efa\u8bae\u4f7f\u7528ANSI-compliant \u65b9\u5f0f\u6765\u5305\u542b\u6807\u51c6\u51fd\u6570\u5e93\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>5.2 \u547d\u540d\u7a7a\u95f4 (Namespaces) \u901a\u8fc7\u4f7f\u7528\u547d\u540d\u7a7a\u95f4(Namespaces)\u6211\u4eec\u53ef\u4ee5\u5c06\u4e00\u7ec4\u5168\u5c40\u8303\u56f4\u6709\u6548\u7684\u7c7b\u3001\u5bf9\u8c61\u6216\u51fd\u6570\u7ec4\u7ec7\u5230\u4e00\u4e2a\u540d\u5b57\u4e0b\u9762\u3002\u6362\u79cd\u8bf4\u6cd5\uff0c\u5c31\u662f\u5b83\u5c06\u5168\u5c40\u8303\u56f4\u5206\u5272\u6210\u8bb8\u591a\u5b50\u57df\u8303\u56f4\uff0c\u6bcf\u4e2a\u5b50\u57df\u8303\u56f4\u53eb\u505a\u4e00\u4e2a\u547d\u540d\u7a7a\u95f4(namespaces). \u4f7f\u7528\u547d\u540d\u7a7a\u95f4\u7684\u683c\u5f0f\u662f\uff1a namespace identifier { namespace-body } \u8fd9\u91ccidentifier \u662f\u4e00\u4e2a\u6709\u6548\u7684\u6807\u793a\u7b26\uff0cnamespace-body \u662f\u8be5\u547d\u540d\u7a7a\u95f4\u5305\u542b\u7684\u4e00\u7ec4\u7c7b\u3001\u5bf9\u8c61\u548c\u51fd\u6570\u3002\u4f8b\u5982\uff1a namespace general { int a, b; } \u5728\u8fd9\u4e2a\u4f8b\u5b50\u4e2d\uff0ca \u548c b \u662f\u547d\u540d\u7a7a\u95f4general\u4e2d\u7684\u6574\u578b\u53d8\u91cf\u3002\u8981\u60f3\u5728\u8fd9\u4e2a\u540d\u7a7a\u95f4\u5916\u9762\u8bbf\u95ee\u8fd9\u4e24\u4e2a\u53d8\u91cf\uff0c\u6211\u4eec\u5fc5\u987b\u4f7f\u7528\u8303\u56f4\u64cd\u4f5c\u7b26::\u3002\u4f8b\u5982\uff0c\u8981\u60f3\u8bbf\u95ee\u524d\u9762\u7684\u4e24\u4e2a\u53d8\u91cf\uff0c\u6211\u4eec\u9700\u8981\u8fd9\u6837\u5199\uff1a general::ageneral::b \u547d\u540d\u7a7a\u95f4(namespaces)\u7684\u4f5c\u7528\u5728\u4e8e\u5168\u5c40\u5bf9\u8c61\u6216\u51fd\u6570\u5f88\u6709\u53ef\u80fd\u91cd\u540d\u800c\u9020\u6210\u91cd\u590d\u5b9a\u4e49\u7684\u9519\u8bef\uff0c\u547d\u540d\u7a7a\u95f4\u7684\u4f7f\u7528\u53ef\u4ee5\u907f\u514d\u8fd9\u4e9b\u9519\u8bef\u7684\u53d1\u751f\u3002\u4f8b\u5982\uff1a \/\/ namespaces #include &lt;iostream.h&gt; namespace first { int var = 5; } namespace second { double var = 3.1416; } int main () { cout &lt;&lt; first::var &lt;&lt; endl; [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":361,"menu_order":1,"comment_status":"closed","ping_status":"closed","template":"","meta":[],"_links":{"self":[{"href":"https:\/\/www.prglab.com\/blog\/wp-json\/wp\/v2\/pages\/367"}],"collection":[{"href":"https:\/\/www.prglab.com\/blog\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/www.prglab.com\/blog\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/www.prglab.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.prglab.com\/blog\/wp-json\/wp\/v2\/comments?post=367"}],"version-history":[{"count":1,"href":"https:\/\/www.prglab.com\/blog\/wp-json\/wp\/v2\/pages\/367\/revisions"}],"predecessor-version":[{"id":368,"href":"https:\/\/www.prglab.com\/blog\/wp-json\/wp\/v2\/pages\/367\/revisions\/368"}],"up":[{"embeddable":true,"href":"https:\/\/www.prglab.com\/blog\/wp-json\/wp\/v2\/pages\/361"}],"wp:attachment":[{"href":"https:\/\/www.prglab.com\/blog\/wp-json\/wp\/v2\/media?parent=367"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}