{"id":430687,"date":"2021-04-18T11:12:02","date_gmt":"2021-04-18T03:12:02","guid":{"rendered":"http:\/\/4563.org\/?p=430687"},"modified":"2021-04-18T11:12:02","modified_gmt":"2021-04-18T03:12:02","slug":"%e8%af%b7%e6%95%99%e4%b8%80%e4%b8%aa-stl-%e7%9a%84%e9%97%ae%e9%a2%98","status":"publish","type":"post","link":"http:\/\/4563.org\/?p=430687","title":{"rendered":"\u8bf7\u6559\u4e00\u4e2a STL \u7684\u95ee\u9898"},"content":{"rendered":"
\n
\n
\n

\u8bf7\u6559\u4e00\u4e2a STL \u7684\u95ee\u9898 <\/h1>\n

<\/p>\n

\n
\u8cc7\u6df1\u5927\u4f6c : pabupa <\/span> <\/i> 6<\/span> <\/div>\n
<\/div>\n<\/p><\/div>\n<\/p><\/div>\n<\/p><\/div>\n
<\/p>\n
map<int, int> m; m[12] = 45; \/\/ \u8fd9\u662f\u600e\u4e48\u5b9e\u73b0\u7684\uff1f <\/code><\/pre>\n
\u5b83\u53ea\u662f\u8fd4\u56de\u4e86\u4e00\u4e2aint&<\/code>\uff0c\u800c\u4e14\u8fd8\u4e0d\u5b58\u5728\u3002\u4e3a\u4ec0\u4e48\u80fd\u8d4b\u503c\u554a\uff1f<\/p>\n
\u6e90\u7801\u771f\u7684\u770b\u4e0d\u61c2\uff0c\u2026\u2026<\/p>\n<\/p><\/div>\n
 \u5927\u4f6c\u6709\u8a71\u8aaa<\/b> (20<\/span>)        <\/div>\n
 <\/div>\n<\/p><\/div>\n<\/p><\/div>\n
    \n
  • \n
    \n
    \n
     \u4e3b<\/span> \u8cc7\u6df1\u5927\u4f6c : pabupa <\/span>  <\/div>\n
     <\/i>            <\/span> <\/div>\n<\/p><\/div>\n
                                                                 (#`O\u2032)\u5582\uff1f\u6ca1\u4eba\u5417\uff1f                                                            <\/div>\n<\/p><\/div>\n<\/li>\n
  • \n
    \n
    \n
     \u8cc7\u6df1\u5927\u4f6c : keygen88 <\/span>  <\/div>\n
     <\/i>            <\/span> <\/div>\n<\/p><\/div>\n
                                                                 \u91cd\u8f7d\u4e86[]\u5427\uff0c                                                            <\/div>\n<\/p><\/div>\n<\/li>\n
  • \n
    \n
    \n
     \u8cc7\u6df1\u5927\u4f6c : jmc891205 <\/span>  <\/div>\n
     <\/i>            <\/span> <\/div>\n<\/p><\/div>\n
                                                                 \u5148\u63d2\u5165\u7136\u540e\u8d4b\u503c\u5427
    https:\/\/en.cppreference.com\/w\/cpp\/container\/map\/operator_at                                                            <\/div>\n<\/p><\/div>\n<\/li>\n
  • \n
    \n
    \n
     \u8cc7\u6df1\u5927\u4f6c : nightwitch <\/span>  <\/div>\n
     <\/i>            <\/span> <\/div>\n<\/p><\/div>\n
     \"\u8bf7\u6559\u4e00\u4e2a
    \u591a\u770b\u6807\u51c6\u554a\u3002\u6807\u51c6\u660e\u786e\u544a\u8bc9\u4e86\u5982\u679c key \u4e0d\u5b58\u5728\uff0c\u4f1a\u5148\u6267\u884c\u4e00\u6b21 insert \u3002<\/p>\n
    llvm \u771f\u6b63\u7684\u5b9e\u73b0\u5728\u8fd9\u91cc
    https:\/\/github.com\/llvm-mirror\/libcxx\/blob\/78d6a7767ed57b50122a161b91f59f19c9bd0d19\/include\/__tree#L2126<\/p>\n
    \u5b83\u4f1a\u5148\u5bfb\u627e\u5185\u90e8\u662f\u5426\u5b58\u5728\u8fd9\u4e2a\u503c\uff0c\u5982\u679c\u4e0d\u5b58\u5728\u5c31\u4f1a\u6784\u9020\u3002                                                            <\/p><\/div>\n<\/p><\/div>\n<\/li>\n
  • \n
    \n
    \n
     \u4e3b<\/span> \u8cc7\u6df1\u5927\u4f6c : pabupa <\/span>  <\/div>\n
     <\/i>            <\/span> <\/div>\n<\/p><\/div>\n
                                                                 @nightwitch #4 \u90a3\u5bf9\u4e8e\u53ea\u8bfb\u7684\u60c5\u51b5\u6765\u8bf4\uff0c\u4e0d\u5c31\u591a\u4f59\u4e86\u5417\uff1f\u800c\u4e14\u5982\u679c V \u4e0d\u80fd\u65e0\u53c2\u6784\u9020\u7684\u8bdd\uff0c\u4e0d\u4e45\u4e0d\u80fd\u7528\u4e86\u5417\uff1f                                                            <\/div>\n<\/p><\/div>\n<\/li>\n
  • \n
    \n
    \n
     \u8cc7\u6df1\u5927\u4f6c : hello2060 <\/span>  <\/div>\n
     <\/i>            <\/span> <\/div>\n<\/p><\/div>\n
                                                                 \u5df2\u7ecf\u5fd8\u4e86 c++\u4e86\uff0c\u8fd9\u4e2a\u4f60\u4e0d\u662f\u8bb0\u4f4f\u5c31\u884c\u4e86\u5417\uff1f<\/p>\n
    \u5b83\u53ea\u662f\u8fd4\u56de\u4e86\u4e00\u4e2a int&\uff0c\u800c\u4e14\u8fd8\u4e0d\u5b58\u5728 —— \u4e0d\u5b58\u5728\u4f60\u662f\u600e\u4e48\u77e5\u9053\u7684\uff0c\u4e5f\u8bb8\u8fd9\u4e2a\u8868\u8fbe\u5f0f\u5728\u5de6\u8fb9\u7684\u65f6\u5019\u4f1a\u81ea\u52a8\u521b\u5efa\u5462\uff1f\u4f60\u9884\u8bbe\u5b83\u4e0d\u5b58\u5728\uff0c\u6240\u4ee5\u65e0\u6cd5\u8d4b\u503c\uff0c\u4f46\u660e\u660e\u53ef\u4ee5\u8d4b\u503c\uff0c\u90a3\u4e0d\u5c31\u8bf4\u660e\u4f60\u4e0d\u5b58\u5728\u7684\u5047\u8bbe\u662f\u9519\u8bef\u7684\u5417                                                            <\/p><\/div>\n<\/p><\/div>\n<\/li>\n
  • \n
    \n
    \n
     \u8cc7\u6df1\u5927\u4f6c : hello2060 <\/span>  <\/div>\n
     <\/i>            <\/span> <\/div>\n<\/p><\/div>\n
                                                                 @pabupa \u53ea\u8bfb\u4e0d\u4f1a\u63d2\u5165\u5427\u3002\u3002                                                            <\/div>\n<\/p><\/div>\n<\/li>\n
  • \n
    \n
    \n
     \u4e3b<\/span> \u8cc7\u6df1\u5927\u4f6c : pabupa <\/span>  <\/div>\n
     <\/i>            <\/span> <\/div>\n<\/p><\/div>\n
                                                                 @hello2060 #7 \u5b83\u6ca1\u6709\u529e\u6cd5\u533a\u5206\u7684\u2026\u2026                                                            <\/div>\n<\/p><\/div>\n<\/li>\n
  • \n
    \n
    \n
     \u8cc7\u6df1\u5927\u4f6c : ipwx <\/span>  <\/div>\n
     <\/i>            <\/span> <\/div>\n<\/p><\/div>\n
                                                                 \u53ea\u8bfb\u8c03\u7528 const value_type& operator[](const key_type&) const
    \u53ef\u53d8\u8c03\u7528 value_type7 operator[](const key_type&)<\/p>\n
    \u51fd\u6570\u672b\u5c3e\u6709\u6ca1\u6709\u4fee\u9970\u7b26 const\uff0c\u5728 C++ \u91cc\u9762\u662f\u4e24\u4e2a\u4e0d\u540c\u7684\u6210\u5458\u51fd\u6570\u3002
    ====<\/p>\n
    \u4f46\u662f\u8fd9\u91cc\u6709\u4e2a\u5751\u3002\u5982\u679c\u4f60\u64cd\u4f5c\u7684\u662f\u53ef\u53d8\u5bf9\u8c61\uff0c\u4f60\u7684 value_type \u6709\u9ed8\u8ba4\u6784\u9020\u51fd\u6570\uff0c\u5982\u679c\u4f60\u4f7f\u7528 <\/p>\n
    std::cout << m[key] << std::endl;<\/p>\n
    \u90a3\u4e48\u5982\u679c key \u4e0d\u5b58\u5728\uff0c\u5728\u67d0\u4e9b\u7248\u672c\u7684 STL \u771f\u7684\u4f1a\u521b\u5efa\u51fa\u8fd9\u4e2a\u5bf9\u8c61\u3002\u6211\u5c31\u88ab\u5751\u8fc7\u3002                                                            <\/p><\/div>\n<\/p><\/div>\n<\/li>\n
  • \n
    \n
    \n
     \u8cc7\u6df1\u5927\u4f6c : across <\/span>  <\/div>\n
     <\/i>            <\/span> <\/div>\n<\/p><\/div>\n
                                                                 mapped_type& operator[] (key_type&& k);<\/p>\n
    C++11 \u91cc\u9762\u52a0\u4e86\u4e2a\u53f3\u503c\u5f15\u7528                                                            <\/p><\/div>\n<\/p><\/div>\n<\/li>\n
  • \n
    \n
    \n
     \u8cc7\u6df1\u5927\u4f6c : across <\/span>  <\/div>\n
     <\/i>            <\/span> <\/div>\n<\/p><\/div>\n
                                                                 @across \u54e6\uff0c\u7b54\u6b6a\u4e86\u3002 \u8fd9\u4e2a\u53d6\u503c\u4e0d\u662f const \u7684\uff0c\u8fd4\u56de\u65f6\u5185\u90e8\u5df2\u7ecf\u521b\u5efa\u8fc7\u53d8\u91cf\u4e86\u3002\u627e\u6807\u51c6\u89e3\u91ca\u90fd\u6709\u8bf4\u7684\u3002
    http:\/\/www.cplusplus.com\/reference\/map\/map\/operator[]\/                                                            <\/div>\n<\/p><\/div>\n<\/li>\n
  • \n
    \n
    \n
     \u8cc7\u6df1\u5927\u4f6c : nightwitch <\/span>  <\/div>\n
     <\/i>            <\/span> <\/div>\n<\/p><\/div>\n
                                                                 @pabupa https:\/\/en.cppreference.com\/w\/cpp\/container\/map\/operator_at
    \u4ed4\u7ec6\u770b\u6807\u51c6\u5427\u3002
    1. \u53ea\u8bfb\u7684\u65f6\u5019 map \u63d0\u4f9b\u4e86 at \u51fd\u6570\uff0c\u5bf9\u4e8e\u4e0d\u5b58\u5728\u7684 key \u4f1a\u629b\u5f02\u5e38
    2. operaotr[]\u5f3a\u5236\u8981\u6c42\u652f\u6301\u65e0\u53c2\u6784\u9020, \u5426\u5219\u7f16\u8bd1\u7684\u65f6\u5019\u4f1a\u8fc7\u4e0d\u4e86\u7f16\u8bd1\u3002                                                            <\/div>\n<\/p><\/div>\n<\/li>\n
  • \n
    \n
    \n
     \u4e3b<\/span> \u8cc7\u6df1\u5927\u4f6c : pabupa <\/span>  <\/div>\n
     <\/i>            <\/span> <\/div>\n<\/p><\/div>\n
                                                                 @ipwx #9 \u8c22\u8c22\uff0c\u61c2\u4e86\u2026\u2026
    @nightwitch #12 \u6211\u548c\u4f60\u6709\u4ec7\u5417\uff1f\u2026\u2026\u4e0d\u8fc7\u8fd8\u662f\u8c22\u8c22                                                            <\/div>\n<\/p><\/div>\n<\/li>\n
  • \n
    \n
    \n
     \u8cc7\u6df1\u5927\u4f6c : mogg <\/span>  <\/div>\n
     <\/i>            <\/span> <\/div>\n<\/p><\/div>\n
                                                                 \u53ea\u8bfb\u7528 find \u5224\u65ad\u8fed\u4ee3\u5668\uff0c\u6216\u8005\u5148 count \u518d\u53d6\u503c
    \u8bfb\u53d6\u4e00\u6b21\u4e8b\u5b9e\u4e0a\u8981\u8fd4\u56de\u4e24\u4e2a\u503c\uff0c\u662f\u5426\u5b58\u5728\u548c\u503c\u7684\u5185\u5bb9\u3002stl \u7684\u5e74\u4ee3\u8fd8\u6ca1\u6709 std::optional \uff08 c++17 \uff09\uff0c\u6ca1\u6709\u529e\u6cd5\u8868\u793a\u8fd4\u56de\u591a\u4e2a\u503c\uff0c\u603b\u4e0d\u80fd map[x] = y \u7ed9\u4f60\u62a5\u4e2a error \u51fa\u6765\u5427                                                            <\/div>\n<\/p><\/div>\n<\/li>\n
  • \n
    \n
    \n
     \u8cc7\u6df1\u5927\u4f6c : nightl2018 <\/span>  <\/div>\n
     <\/i>            <\/span> <\/div>\n<\/p><\/div>\n
                                                                 \u53ea\u8bfb\u7528 find \u5148\u627e\u4e00\u4e0b\u5b58\u4e0d\u5b58\u5728\u3002
    “`
    auto it = m.find(x);
    if (it != m.end() ) cerr<<*it<<endl;
    else cerr<<“Not exist.”<<endl;
    “`                                                            <\/div>\n<\/p><\/div>\n<\/li>\n
  • \n
    \n
    \n
     \u8cc7\u6df1\u5927\u4f6c : nightl2018 <\/span>  <\/div>\n
     <\/i>            <\/span> <\/div>\n<\/p><\/div>\n
                                                                 \u521d\u770b\u89c9\u5f97\u5f88\u602a\uff0c\u4f46\u662f\u7ed3\u5408\u5176\u4ed6 STL \u6807\u51c6\uff0c\u5c31\u76f8\u5f53\u4f18\u7f8e\u3002\u6bd4\u5982 set:
    “`
    set<int> s;
    if(s.insert(x).second == true) cerr<<“Insert success”<<endl;
    else cerr<<“Already exsit”<<endl;
    “`                                                            <\/div>\n<\/p><\/div>\n<\/li>\n
  • \n
    \n
    \n
     \u8cc7\u6df1\u5927\u4f6c : Akiyu <\/span>  <\/div>\n
     <\/i>            <\/span> <\/div>\n<\/p><\/div>\n
                                                                 \u597d\u50cf\u5f88\u591a\u4eba\u90fd\u5df2\u7ecf\u56de\u7b54\u4e86, \u4e0d\u8fc7\u6211\u8fd8\u662f\u8bf4\u4e00\u4e0b\u5427.<\/p>\n
    “\u5b83\u53ea\u662f\u8fd4\u56de\u4e86\u4e00\u4e2a int&\uff0c\u800c\u4e14\u8fd8\u4e0d\u5b58\u5728\u3002\u4e3a\u4ec0\u4e48\u80fd\u8d4b\u503c\u554a\uff1f”<\/p>\n
    “\u5b83\u53ea\u662f\u8fd4\u56de\u4e86\u4e00\u4e2a int&”
    \u662f\u7684, \u5b83\u53ea\u662f\u8fd4\u56de\u4e86\u4e00\u4e2a int&. \u4f46\u8fd9\u5df2\u7ecf\u591f\u4e86. int \u662f\u4f60 map value \u7684\u7c7b\u578b, \u800c & \u4fdd\u8bc1\u4f60\u7684\u4fee\u6539\u751f\u6548\u4e8e map \u5185\u90e8\u6570\u636e.<\/p>\n
    “\u800c\u4e14\u8fd8\u4e0d\u5b58\u5728”
    \u5b58\u5728\u7684, \u5bf9\u4e8e map \u7684 [] \u91cd\u8f7d\u800c\u8a00, \u5f53\u4f60\u8bbf\u95ee\u7684\u5143\u7d20\u4e0d\u5b58\u5728\u65f6, \u4f1a\u521b\u5efa\u4e00\u4e2a(\u7c7b\u578b\u7684\u96f6\u503c). \u800c\u5b58\u5728\u65f6, \u4f1a\u8fd4\u56de valueType&. \u6240\u4ee5\u65e0\u8bba\u5982\u4f55, \u90fd\u4f1a\u6709\u5143\u7d20\u5b58\u5728.
    (PS: \u8fd9\u91cc\u6709\u4e2a\u70b9\u9700\u8981\u6ce8\u610f, \u5f53\u4f60\u60f3\u77e5\u9053 map \u4e2d\u662f\u5426\u5b58\u5728\u4e00\u4e2a\u5143\u7d20\u65f6, \u4f60\u4e0d\u80fd\u7528 []. \u56e0\u4e3a\u8fd9\u4e00\u5b9a\u4f1a\u5b58\u5728, \u4f60\u6216\u8bb8\u53ef\u4ee5\u7528\u8fd9\u4e2a\u7c7b\u578b\u7684\u96f6\u503c\u6765\u5224\u65ad\u662f\u5426\u662f\u65b0\u521b\u5efa\u7684, \u4f46\u8fd9\u5e76\u4e0d\u597d, \u66f4\u597d\u7684\u65b9\u5f0f\u662f: mapName.find(key) == maoName.end(); )                                                            <\/div>\n<\/p><\/div>\n<\/li>\n
  • \n
    \n
    \n
     \u8cc7\u6df1\u5927\u4f6c : FrankHB <\/span>  <\/div>\n
     <\/i>            <\/span> <\/div>\n<\/p><\/div>\n
                                                                 @ipwx \u9ebb\u70e6\u5148\u8bb0\u6e05\u695a map::operator[] \u8981\u6c42 non-const \u518d\u6765\u79d1\u666e\uff0c\u8c22\u8c22\u3002<\/p>\n
    \u600e\u4e48\u8fd9\u4e48\u4e45\u90fd\u6ca1\u4e2a\u63d0\u51fa\u6765 map::operator[] \u65e9\u5c31\u6539\u7528 try_emplace \u5b9a\u4e49\u7684\uff1f<\/p>\n
    WG21 N4860
    22.4.4.3 Element access
    [map.access]
    mapped_type& operator[](const key_type& x);
    1 Effects:
    Equivalent to:
    return try_emplace(x).first->second;
    mapped_type& operator[](key_type&& x);
    2 Effects:
    Equivalent to:
    return try_emplace(move(x)).first->second;<\/p>\n
    \u771f\u6298\u817e\u6e90\u7801\u4e5f\u884c\uff0c\u7ed9\u4f60\u4e2a\u73b0\u6210\u6ca1\u5230\u5904 __ \u7684\u5b9e\u73b0\u597d\u4e86\uff0cC++11 \u4e0b\u5b9e\u73b0 C++17+ API\uff0c\u9644\u52a0\u4fdd\u8bc1 incomplete value_type \u80fd\u7528\uff1a<\/p>\n
    https:\/\/github.com\/FrankHB\/YSLib\/blob\/master\/YBase\/include\/ystdex\/map.hpp#L313
    https:\/\/github.com\/FrankHB\/YSLib\/blob\/master\/YBase\/include\/ystdex\/tree.h#L1885<\/p>\n
    \u4e0d\u8fc7\u53ef\u80fd\u4e0d\u5982\u7406\u89e3\u4e2a\u5916\u6302\u5f0f try_emplace \u7684\u903b\u8f91\u9876\u7528\u70b9\uff1a<\/p>\n
    https:\/\/github.com\/FrankHB\/YSLib\/blob\/master\/YBase\/include\/ystdex\/container.hpp#L1039                                                            <\/p><\/div>\n<\/p><\/div>\n<\/li>\n
  • \n
    \n
    \n
     \u8cc7\u6df1\u5927\u4f6c : opentrade <\/span>  <\/div>\n
     <\/i>            <\/span> <\/div>\n<\/p><\/div>\n
                                                                 \u60f3\u5230\u8bfb\u7814\u7684\u65f6\u5019\u6709\u4e00\u6b21\u4e00\u4e2a\u5e08\u5f1f\u95ee\u6211\u4e3a\u4ec0\u4e48 Cpp \u91cc\u51fd\u6570\u91cc\u7684\u5c40\u90e8\u53d8\u91cf\u5916\u8fb9\u4e0d\u80fd\u8bbf\u95ee\u3002                                                            <\/div>\n<\/p><\/div>\n<\/li>\n
  • \n
    \n
    \n
     \u8cc7\u6df1\u5927\u4f6c : unlighted <\/span>  <\/div>\n
     <\/i>            <\/span> <\/div>\n<\/p><\/div>\n
                                                                 cppreference.com                                                            <\/div>\n<\/p><\/div>\n<\/li>\n
  • \n","protected":false},"excerpt":{"rendered":"
    \u8bf7\u6559\u4e00\u4e2a STL \u7684\u95ee\u9898 \u8cc7\u6df1\u5927\u4f6c…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[],"tags":[],"_links":{"self":[{"href":"http:\/\/4563.org\/index.php?rest_route=\/wp\/v2\/posts\/430687"}],"collection":[{"href":"http:\/\/4563.org\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/4563.org\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/4563.org\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/4563.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=430687"}],"version-history":[{"count":0,"href":"http:\/\/4563.org\/index.php?rest_route=\/wp\/v2\/posts\/430687\/revisions"}],"wp:attachment":[{"href":"http:\/\/4563.org\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=430687"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/4563.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=430687"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/4563.org\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=430687"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}