{"id":115701,"date":"2026-10-13T08:24:54","date_gmt":"2026-10-13T00:24:54","guid":{"rendered":"https:\/\/www.wsisp.com\/helps\/115701.html"},"modified":"2026-10-13T08:24:54","modified_gmt":"2026-10-13T00:24:54","slug":"c-%e6%96%87%e4%bb%b6%e8%af%bb%e5%86%99%e5%ae%9e%e6%88%98%ef%bc%9aofstream-%e9%bb%98%e8%ae%a4%e6%b8%85%e7%a9%ba%e6%96%87%e4%bb%b6%e3%80%81getline-%e4%b8%8e-%ef%bc%9e%ef%bc%9e-%e6%b7%b7%e7%94%a8","status":"publish","type":"post","link":"https:\/\/www.wsisp.com\/helps\/115701.html","title":{"rendered":"C++ \u6587\u4ef6\u8bfb\u5199\u5b9e\u6218\uff1aofstream \u9ed8\u8ba4\u6e05\u7a7a\u6587\u4ef6\u3001getline \u4e0e \uff1e\uff1e \u6df7\u7528\u7684\u5751"},"content":{"rendered":"

\u6587\u4ef6 I\/O \u662f\u90a3\u79cd\u300c\u8bed\u6cd5\u4e94\u5206\u949f\u3001\u8e29\u5751\u4e09\u5e74\u300d\u7684\u4e1c\u897f\u3002ofstream \u7684\u9ed8\u8ba4\u6a21\u5f0f\u91cc\u85cf\u7740 trunc，\u7b2c\u4e8c\u6b21\u6253\u5f00\u540c\u4e00\u4e2a\u8def\u5f84\u5c31\u628a\u4e0a\u6b21\u7684\u5185\u5bb9\u6e05\u7a7a\u4e86；in >> id \u4e4b\u540e\u63a5 std::getline \u53ea\u4f1a\u62ff\u5230\u4e00\u4e2a\u7a7a\u4e32，\u56e0\u4e3a\u6362\u884c\u7b26\u8fd8\u7559\u5728\u7f13\u51b2\u533a\u91cc；\u800c std::ofstream \u9ed8\u8ba4\u4e0d\u629b\u5f02\u5e38，\u78c1\u76d8\u6ee1\u3001\u76ee\u5f55\u4e0d\u5b58\u5728\u3001\u6743\u9650\u4e0d\u591f，\u5b83\u90fd\u53ea\u662f\u9ed8\u9ed8\u628a failbit \u7f6e\u4e0a，\u7a0b\u5e8f\u7ee7\u7eed\u8dd1\u5f97\u6b22\u3002\u8fd9\u7bc7\u628a\u6253\u5f00\u6a21\u5f0f\u3001\u72b6\u6001\u4f4d\u3001RAII \u548c\u56db\u7c7b\u5178\u578b\u8bfb\u53d6\u65b9\u5f0f\u4e00\u6b21\u8bb2\u900f，\u5e76\u4e14\u6bcf\u4e2a\u793a\u4f8b\u90fd\u7528\u4e34\u65f6\u6587\u4ef6\u3001\u8dd1\u5b8c\u5c31\u5220，\u4fdd\u8bc1\u53ef\u91cd\u590d\u8fd0\u884c\u3002<\/p>\n

1. \u5f15\u5b50：\u4e00\u4e2a\u300c\u5199\u6210\u529f\u300d\u4f46\u5176\u5b9e\u4ec0\u4e48\u90fd\u6ca1\u5199\u7684\u7a0b\u5e8f<\/h3>\n

\u5148\u770b\u8fd9\u4e2a\u5f88\u591a\u4eba\u7b2c\u4e00\u6b21\u5199\u6587\u4ef6\u65f6\u90fd\u5199\u8fc7\u7684\u7248\u672c：<\/p>\n

\/\/ \u53cd\u4f8b，\u4e0d\u8981\u8fd9\u4e48\u5199：\u65e2\u4e0d\u68c0\u67e5\u6253\u5f00\u662f\u5426\u6210\u529f，\u4e5f\u4e0d\u68c0\u67e5\u5199\u5165\u662f\u5426\u6210\u529f<\/span>
\n\/\/ std::ofstream out("\/root\/no_permission\/app.log");<\/span>
\n\/\/ out << "\u91cd\u8981\u65e5\u5fd7\\\\n";<\/span>
\n\/\/ out.close(); \/\/ \u6ca1\u6709\u4efb\u4f55\u8fd4\u56de\u503c\u53ef\u67e5，\u5931\u8d25\u4e86\u4e5f\u4e0d\u77e5\u9053<\/span><\/p>\n

\u8fd9\u6bb5\u4ee3\u7801\u7684\u95ee\u9898\u6709\u4e09\u4e2a，\u800c\u4e14\u90fd\u5728\u7f16\u8bd1\u671f\u5b8c\u5168\u770b\u4e0d\u51fa\u6765：\u76ee\u5f55\u4e0d\u5b58\u5728\u65f6 open \u5931\u8d25，out \u5904\u4e8e fail \u72b6\u6001，\u540e\u9762\u6bcf\u4e00\u53e5 << \u90fd\u4e0d\u8d77\u4f5c\u7528；close() \u7684\u5931\u8d25\u4e5f\u662f\u9759\u9ed8\u7684（\u5b83\u4e0d\u629b\u5f02\u5e38）；\u81f3\u4e8e\u624b\u5199 close()，\u5176\u5b9e\u5927\u591a\u6570\u65f6\u5019\u6839\u672c\u4e0d\u9700\u8981：\u6790\u6784\u4f1a\u5e2e\u4f60\u505a\u3002\u8981\u5f04\u6e05\u695a\u54ea\u4e9b\u4e8b\u8be5\u4ea4\u7ed9\u4eba\u3001\u54ea\u4e9b\u4ea4\u7ed9 RAII，\u5148\u628a\u4e09\u4e2a\u6d41\u7c7b\u548c\u5b83\u4eec\u7684\u6253\u5f00\u6a21\u5f0f\u6446\u5e73\u3002<\/p>\n

2. ifstream \/ ofstream \/ fstream \u4e0e\u6253\u5f00\u6a21\u5f0f<\/h3>\n

\u4e09\u4e2a\u7c7b\u90fd\u662f std::basic_ios \u7684\u5b59\u5b50\u8f88，\u533a\u522b\u53ea\u5728\u4e8e\u9ed8\u8ba4\u6253\u5f00\u6a21\u5f0f：<\/p>\n\n\u7c7b\u578b\u9ed8\u8ba4\u6a21\u5f0f\u7528\u9014<\/tr>\n\n\n\n\n
std::ifstream<\/td>\nstd::ios::in<\/td>\n\u53ea\u8bfb<\/td>\n<\/tr>\n
std::ofstream<\/td>\nstd::ios::out | std::ios::trunc<\/td>\n\u53ea\u5199，\u4f1a\u6e05\u7a7a\u5df2\u6709\u6587\u4ef6<\/td>\n<\/tr>\n
std::fstream<\/td>\nstd::ios::in | std::ios::out<\/td>\n\u53ef\u8bfb\u53ef\u5199，\u4e0d\u6e05\u7a7a（\u6587\u4ef6\u5fc5\u987b\u5df2\u5b58\u5728）<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

\u6bcf\u4e2a\u6a21\u5f0f\u4f4d\u7684\u542b\u4e49，\u4ee5\u53ca\u5e38\u89c1\u7ec4\u5408：<\/p>\n\n\u6a21\u5f0f\u4f4d\u542b\u4e49\u5173\u952e\u70b9<\/tr>\n\n\n\n\n\n\n\n
std::ios::in<\/td>\n\u5141\u8bb8\u8bfb<\/td>\nifstream \u7684\u9ed8\u8ba4\u503c<\/td>\n<\/tr>\n
std::ios::out<\/td>\n\u5141\u8bb8\u5199<\/td>\n\u5355\u72ec\u7ed9 ofstream \u65f6\u4f1a\u9690\u542b trunc<\/td>\n<\/tr>\n
std::ios::trunc<\/td>\n\u6253\u5f00\u65f6\u6e05\u7a7a\u6587\u4ef6<\/td>\n\u548c out \u4e00\u8d77\u7528\u662f\u300c\u8986\u76d6\u5199\u300d<\/td>\n<\/tr>\n
std::ios::app<\/td>\n\u6bcf\u6b21\u5199\u5165\u524d\u5b9a\u4f4d\u5230\u6587\u4ef6\u672b\u5c3e<\/td>\n\u8ffd\u52a0\u65e5\u5fd7\u7528\u8fd9\u4e2a，\u9690\u542b out<\/td>\n<\/tr>\n
std::ios::ate<\/td>\n\u6253\u5f00\u540e\u7acb\u5373\u5b9a\u4f4d\u5230\u672b\u5c3e，\u4e4b\u540e\u53ef\u4ee5\u4efb\u610f seek<\/td>\n\u5e38\u7528\u6765\u300c\u6253\u5f00\u5c31\u80fd\u95ee\u6587\u4ef6\u591a\u5927\u300d<\/td>\n<\/tr>\n
std::ios::binary<\/td>\n\u4e0d\u505a\u4efb\u4f55\u6362\u884c\u7ffb\u8bd1，\u6309\u5b57\u8282\u8bfb\u5199<\/td>\nWindows \u4e0a\u4e0d\u52a0\u5b83\u5c31\u4f1a\u88ab\u6539 \\\\r\\\\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

\u5e38\u89c1\u7684\u6309\u4f4d\u6216\u7ec4\u5408\u901f\u67e5：<\/p>\n\n\u60f3\u8981\u7684\u8bed\u4e49\u6a21\u5f0f<\/tr>\n\n\n\n\n\n\n\n
\u8bfb\u4e00\u4e2a\u5df2\u5b58\u5728\u7684\u6587\u4ef6<\/td>\nin<\/td>\n<\/tr>\n
\u8986\u76d6\u5199（\u6e05\u7a7a\u91cd\u6765）<\/td>\nout（\u7b49\u4ef7 out|trunc）<\/td>\n<\/tr>\n
\u8ffd\u52a0\u5199（\u4fdd\u7559\u65e7\u5185\u5bb9）<\/td>\nout|app<\/td>\n<\/tr>\n
\u539f\u5730\u6539\u5176\u4e2d\u4e00\u6bb5\u5b57\u8282<\/td>\nin|out \u6216 in|out|binary<\/td>\n<\/tr>\n
\u6253\u5f00\u5c31\u62ff\u5230\u6587\u4ef6\u5927\u5c0f<\/td>\nin|ate<\/td>\n<\/tr>\n
\u4e8c\u8fdb\u5236\u8bfb \/ \u5199<\/td>\nin|binary \/ out|binary<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

\u5b98\u65b9\u6587\u6863：std::basic_ifstream\u3001std::basic_filebuf::open \u7684\u6a21\u5f0f\u8868<\/p>\n

3. \u7b2c\u4e00\u4e2a\u5751：ofstream \u7684\u9ed8\u8ba4\u6a21\u5f0f\u4f1a\u6e05\u7a7a\u6587\u4ef6<\/h3>\n

std::ofstream out(path); \u8fd9\u4e00\u53e5\u91cc\u7684\u9ed8\u8ba4\u6a21\u5f0f\u662f out | trunc，\u6240\u4ee5\u53ea\u8981\u8def\u5f84\u5b58\u5728，\u5185\u5bb9\u7acb\u523b\u6ca1\u4e86\u3002\u6539\u6210\u8ffd\u52a0\u5fc5\u987b\u663e\u5f0f\u5199 app：<\/p>\n

\/\/ file_trunc.cpp \u2014 \u7f16\u8bd1: g++ -std=c++17 -Wall -O2 file_trunc.cpp -o demo<\/span>
\n#<\/span>include<\/span> <cstdio><\/span><\/span>
\n#<\/span>include<\/span> <fstream><\/span><\/span>
\n#<\/span>include<\/span> <iostream><\/span><\/span>
\n#<\/span>include<\/span> <string><\/span><\/span><\/p>\n

constexpr<\/span> const<\/span> char<\/span>*<\/span> kPath =<\/span> "miao_tmp_trunc.txt"<\/span>;<\/span><\/p>\n

std::<\/span>string slurp<\/span>(<\/span>const<\/span> char<\/span>*<\/span> p)<\/span> {<\/span>
\n std::<\/span>ifstream in<\/span>(<\/span>p)<\/span>;<\/span>
\n std::<\/span>string all;<\/span>
\n std::<\/span>string line;<\/span>
\n while<\/span> (<\/span>std::<\/span>getline<\/span>(<\/span>in,<\/span> line)<\/span>)<\/span> {<\/span> all +=<\/span> line;<\/span> all +=<\/span> '|'<\/span>;<\/span> }<\/span>
\n return<\/span> all;<\/span>
\n}<\/span><\/p>\n

int<\/span> main<\/span>(<\/span>)<\/span> {<\/span>
\n {<\/span>
\n std::<\/span>ofstream out<\/span>(<\/span>kPath)<\/span>;<\/span> \/\/ \u9ed8\u8ba4 out|trunc<\/span>
\n out <<<\/span> "first\\\\n"<\/span>;<\/span>
\n }<\/span>
\n std::<\/span>cout <<<\/span> "\u5199\u5165\u4e00\u6b21\u540e: "<\/span> <<<\/span> slurp<\/span>(<\/span>kPath)<\/span> <<<\/span> '\\\\n'<\/span>;<\/span><\/p>\n

{<\/span>
\n std::<\/span>ofstream out<\/span>(<\/span>kPath)<\/span>;<\/span> \/\/ \u53c8\u622a\u65ad\u4e00\u6b21，\u65e7\u5185\u5bb9\u6ca1\u4e86<\/span>
\n out <<<\/span> "second\\\\n"<\/span>;<\/span>
\n }<\/span>
\n std::<\/span>cout <<<\/span> "\u518d\u5199\u4e00\u6b21\u540e: "<\/span> <<<\/span> slurp<\/span>(<\/span>kPath)<\/span> <<<\/span> '\\\\n'<\/span>;<\/span><\/p>\n

{<\/span>
\n std::<\/span>ofstream out<\/span>(<\/span>kPath,<\/span> std::<\/span>ios::<\/span>out |<\/span> std::<\/span>ios::<\/span>app)<\/span>;<\/span> \/\/ \u8ffd\u52a0<\/span>
\n out <<<\/span> "third\\\\n"<\/span>;<\/span>
\n }<\/span>
\n std::<\/span>cout <<<\/span> "app \u8ffd\u52a0\u540e: "<\/span> <<<\/span> slurp<\/span>(<\/span>kPath)<\/span> <<<\/span> '\\\\n'<\/span>;<\/span><\/p>\n

std::<\/span>remove<\/span>(<\/span>kPath)<\/span>;<\/span>
\n}<\/span><\/p>\n

\u5199\u5165\u4e00\u6b21\u540e: first|
\n\u518d\u5199\u4e00\u6b21\u540e: second|
\napp \u8ffd\u52a0\u540e: second|third|<\/p>\n

\u6ce8\u610f\u6bcf\u6bb5\u5199\u6587\u4ef6\u90fd\u5305\u5728 {} \u91cc\u3002\u8fd9\u4e0d\u662f\u4e3a\u4e86\u597d\u770b：\u79bb\u5f00\u4f5c\u7528\u57df\u65f6 ofstream \u6790\u6784，\u7f13\u51b2\u533a\u4f1a\u88ab flush \u5e76\u5173\u95ed\u6587\u4ef6，\u6240\u4ee5\u4e0b\u4e00\u6bb5\u7684 ifstream \u4e00\u5b9a\u80fd\u8bfb\u5230\u5b8c\u6574\u5185\u5bb9\u3002\u8fd9\u5c31\u662f\u7b2c 5 \u8282\u8981\u8bb2\u7684 RAII\u3002<\/p>\n

4. \u7b2c\u4e8c\u4e2a\u5751：>> \u548c getline \u5bf9\u300c\u7a7a\u767d\u300d\u7684\u7406\u89e3\u4e0d\u540c<\/h3>\n

operator>> \u6309\u7a7a\u767d\u5b57\u7b26（\u7a7a\u683c\u3001\u5236\u8868\u3001\u6362\u884c\u90fd\u7b97）\u5207\u5206\u5e76\u8df3\u8fc7\u524d\u5bfc\u7a7a\u767d；std::getline \u8bfb\u5230\u6362\u884c\u7b26\u4e3a\u6b62\u5e76\u5403\u6389\u90a3\u4e2a\u6362\u884c\u3002\u4e24\u8005\u4e00\u8d77\u7528\u5c31\u51fa\u95ee\u9898：<\/p>\n

\/\/ file_getline.cpp \u2014 \u7f16\u8bd1: g++ -std=c++17 -Wall -O2 file_getline.cpp -o demo<\/span>
\n#<\/span>include<\/span> <cstdio><\/span><\/span>
\n#<\/span>include<\/span> <fstream><\/span><\/span>
\n#<\/span>include<\/span> <iostream><\/span><\/span>
\n#<\/span>include<\/span> <limits><\/span><\/span>
\n#<\/span>include<\/span> <string><\/span><\/span><\/p>\n

constexpr<\/span> const<\/span> char<\/span>*<\/span> kNumPath =<\/span> "miao_tmp_num.txt"<\/span>;<\/span>
\nconstexpr<\/span> const<\/span> char<\/span>*<\/span> kWordPath =<\/span> "miao_tmp_word.txt"<\/span>;<\/span><\/p>\n

int<\/span> main<\/span>(<\/span>)<\/span> {<\/span>
\n {<\/span> std::<\/span>ofstream f<\/span>(<\/span>kNumPath)<\/span>;<\/span> f <<<\/span> "42\\\\nmiao\\\\n"<\/span>;<\/span> }<\/span>
\n {<\/span> std::<\/span>ofstream f<\/span>(<\/span>kWordPath)<\/span>;<\/span> f <<<\/span> "hello world\\\\n"<\/span>;<\/span> }<\/span><\/p>\n

{<\/span>
\n std::<\/span>ifstream in<\/span>(<\/span>kWordPath)<\/span>;<\/span>
\n std::<\/span>string a,<\/span> b;<\/span>
\n in >><\/span> a >><\/span> b;<\/span> \/\/ \u9047\u5230\u7a7a\u767d\u5c31\u65ad<\/span>
\n std::<\/span>cout <<<\/span> ">> \u5206\u8bcd : "<\/span> <<<\/span> a <<<\/span> " | "<\/span> <<<\/span> b <<<\/span> '\\\\n'<\/span>;<\/span>
\n }<\/span>
\n {<\/span>
\n std::<\/span>ifstream in<\/span>(<\/span>kNumPath)<\/span>;<\/span>
\n int<\/span> id =<\/span> 0<\/span>;<\/span>
\n in >><\/span> id;<\/span> \/\/ \u8bfb\u8d70 42，\u505c\u5728\u8be5\u884c\u7684\u6362\u884c\u7b26\u524d<\/span>
\n std::<\/span>string line;<\/span>
\n std::<\/span>getline<\/span>(<\/span>in,<\/span> line)<\/span>;<\/span> \/\/ \u53ea\u62ff\u5230\u4e00\u4e2a\u7a7a\u4e32<\/span>
\n std::<\/span>cout <<<\/span> "\u8e29\u5751 : id="<\/span> <<<\/span> id <<<\/span> " line=["<\/span> <<<\/span> line <<<\/span> "]\\\\n"<\/span>;<\/span>
\n }<\/span>
\n {<\/span>
\n std::<\/span>ifstream in<\/span>(<\/span>kNumPath)<\/span>;<\/span>
\n int<\/span> id =<\/span> 0<\/span>;<\/span>
\n in >><\/span> id;<\/span>
\n in.<\/span>ignore<\/span>(<\/span>std::<\/span>numeric_limits<\/span><<\/span>std::<\/span>streamsize><\/span>::<\/span>max<\/span>(<\/span>)<\/span>,<\/span> '\\\\n'<\/span>)<\/span>;<\/span> \/\/ \u5403\u6389\u884c\u5c3e<\/span>
\n std::<\/span>string line;<\/span>
\n std::<\/span>getline<\/span>(<\/span>in,<\/span> line)<\/span>;<\/span>
\n std::<\/span>cout <<<\/span> "\u6b63\u786e\u59ff\u52bf : id="<\/span> <<<\/span> id <<<\/span> " line=["<\/span> <<<\/span> line <<<\/span> "]\\\\n"<\/span>;<\/span>
\n }<\/span>
\n std::<\/span>remove<\/span>(<\/span>kNumPath)<\/span>;<\/span>
\n std::<\/span>remove<\/span>(<\/span>kWordPath)<\/span>;<\/span>
\n}<\/span><\/p>\n

>> \u5206\u8bcd : hello | world
\n\u8e29\u5751 : id=42 line=[]
\n\u6b63\u786e\u59ff\u52bf : id=42 line=[miao]<\/p>\n

\u4fee\u6cd5\u5c31\u662f\u5728 >> \u4e4b\u540e\u8865\u4e00\u6b21 ignore：\u628a\u5f53\u524d\u884c\u5269\u4e0b\u7684\u5b57\u7b26（\u76f4\u5230\u6362\u884c\u7b26）\u5168\u4e22\u6389\u3002\u53e6\u4e00\u79cd\u540c\u6837\u5e38\u89c1\u7684\u5199\u6cd5\u662f\u5168\u7a0b\u53ea\u7528 getline，\u62ff\u5230\u6574\u884c\u4e4b\u540e\u518d\u7528 std::istringstream \u53bb\u5207\u5206：\u8fd9\u4e5f\u662f\u300aC++ stringstream \u5b9e\u7528\u6307\u5357：\u5206\u8bcd\u89e3\u6790\u3001\u7c7b\u578b\u4e92\u8f6c\u4e0e clear\/str \u7684\u533a\u522b\u300b\u8981\u5c55\u5f00\u7684\u5957\u8def，\u597d\u5904\u662f\u300c\u884c\u300d\u548c\u300c\u5b57\u6bb5\u300d\u4e24\u4e2a\u5c42\u7ea7\u5206\u5f97\u6e05\u6e05\u695a\u695a，\u4e0d\u4f1a\u518d\u51fa\u73b0\u534a\u4e2a\u6362\u884c\u7b26\u5361\u5728\u7f13\u51b2\u533a\u91cc\u7684\u60c5\u51b5\u3002<\/p>\n\n\u9700\u6c42\u8be5\u7528\u7684\u5de5\u5177\u539f\u56e0<\/tr>\n\n\n\n\n\n\n
\u8bfb\u6574\u884c\u3001\u4fdd\u7559\u7a7a\u683c<\/td>\nstd::getline(in, line)<\/td>\n\u53ea\u4ee5\u6362\u884c\u7b26\u4e3a\u754c<\/td>\n<\/tr>\n
\u6309\u7a7a\u767d\u5207\u8bcd（\u4e14\u4e0d\u5728\u4e4e\u884c）<\/td>\nin >> word<\/td>\n\u81ea\u52a8\u8df3\u8fc7\u524d\u5bfc\u7a7a\u767d<\/td>\n<\/tr>\n
\u8bfb\u4e00\u4e2a\u6570\u5b57<\/td>\nin >> value<\/td>\n\u5931\u8d25\u53ea\u7f6e failbit，\u4e0d\u629b<\/td>\n<\/tr>\n
\u5148\u8bfb\u6570\u5b57\u518d\u8bfb\u6574\u884c<\/td>\n>> + ignore + getline<\/td>\n\u5fc5\u987b\u624b\u52a8\u5403\u6389\u6b8b\u7559\u6362\u884c<\/td>\n<\/tr>\n
\u884c\u5185\u518d\u5207\u5b57\u6bb5<\/td>\nstd::istringstream<\/td>\n\u4e24\u5c42\u89e3\u6790，\u4e92\u4e0d\u5e72\u6270<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

5. RAII：\u6790\u6784\u81ea\u52a8 flush + close，\u4f46\u300c\u5199\u6210\u529f\u300d\u8981\u81ea\u5df1\u67e5<\/h3>\n

\u6587\u4ef6\u6d41\u662f\u6807\u51c6\u5e93\u91cc\u7684 RAII \u5178\u8303：std::basic_filebuf \u7684\u6790\u6784\u51fd\u6570\u4f1a\u5173\u95ed\u6587\u4ef6，\u800c std::ofstream \u7684\u6790\u6784\u4f1a\u5148 flush \u8f93\u51fa\u7f13\u51b2\u533a\u3002\u6240\u4ee5\u4e0d\u9700\u8981\u624b\u5199 close()，\u800c\u4e14\u5728\u5f02\u5e38\u8def\u5f84\u4e0a\u4e5f\u5b89\u5168：<\/p>\n

ofstream \u7684\u751f\u547d\u5468\u671f（\u5bf9\u8c61\u5373\u8d44\u6e90）<\/p>\n

std::ofstream out{path}; <- \u6784\u9020：\u6253\u5f00\u6587\u4ef6，\u5931\u8d25\u5219\u7f6e failbit（\u4e0d\u629b）
\n |
\n | out << "…" << 42; <- \u5199\u5165：\u5148\u6512\u5728\u5185\u5b58\u7f13\u51b2\u533a\u91cc
\n | out << "…" << 43;
\n |
\n +— \u4f5c\u7528\u57df\u7ed3\u675f \/ \u5f02\u5e38\u629b\u51fa —+
\n |
\n v
\n \u6790\u6784：flush \u7f13\u51b2\u533a -> \u5173\u95ed\u6587\u4ef6\u63cf\u8ff0\u7b26
\n \u987a\u5e8f\u4fdd\u8bc1：\u6808\u5c55\u5f00\u65f6\u4e5f\u4f1a\u6267\u884c（\u8fd9\u5c31\u662f RAII \u7684\u4ef7\u503c）<\/p>\n

\u624b\u5199 close() \u7684\u552f\u4e00\u6536\u76ca\u662f\u300c\u80fd\u63d0\u524d\u77e5\u9053\u5173\u95ed\u6709\u6ca1\u6709\u5931\u8d25\u300d，
\n \u5de5\u7a0b\u91cc\u66f4\u5e38\u89c1\u7684\u505a\u6cd5\u662f\u5199\u5b8c\u7acb\u523b\u68c0\u67e5\u6d41\u72b6\u6001，\u800c\u4e0d\u662f\u4f9d\u8d56 close()\u3002<\/p>\n

\u5751\u5728\u4e8e**\u300c\u6790\u6784\u4e00\u5b9a\u4f1a\u6267\u884c\u300d\u4e0d\u7b49\u4e8e\u300c\u4e00\u5b9a\u5199\u6210\u529f\u300d**\u3002\u6790\u6784\u4e0d\u505a\u4efb\u4f55\u62a5\u9519，\u78c1\u76d8\u6ee1\u3001\u7ba1\u9053\u5173\u95ed\u3001\u914d\u989d\u8d85\u9650\u90fd\u5728\u8fd9\u91cc\u88ab\u65e0\u58f0\u541e\u6389\u3002\u6240\u4ee5\u6b63\u786e\u59ff\u52bf\u662f\u300c\u5199\u5b8c\u5c31\u67e5\u300d：<\/p>\n

\/\/ \u7247\u6bb5：\u5199\u5b8c\u7acb\u523b\u67e5\u4e00\u6b21，\u628a\u9519\u8bef\u6321\u5728\u8fd8\u80fd\u5904\u7406\u7684\u65f6\u523b<\/span>
\nstd::<\/span>ofstream out<\/span>(<\/span>path,<\/span> std::<\/span>ios::<\/span>out |<\/span> std::<\/span>ios::<\/span>trunc)<\/span>;<\/span>
\nif<\/span> (<\/span>!<\/span>out)<\/span> {<\/span> throw<\/span> std::<\/span>runtime_error<\/span>(<\/span>"\u6253\u5f00\u6587\u4ef6\u5931\u8d25"<\/span>)<\/span>;<\/span> }<\/span>
\nout <<<\/span> "width="<\/span> <<<\/span> width <<<\/span> '\\\\n'<\/span>;<\/span>
\nout.<\/span>flush<\/span>(<\/span>)<\/span>;<\/span> \/\/ \u4e3b\u52a8\u63a8\u8fdb\u5e95\u5c42，\u8ba9\u9519\u8bef\u73b0\u5728\u5c31\u66b4\u9732<\/span>
\nif<\/span> (<\/span>!<\/span>out)<\/span> {<\/span> throw<\/span> std::<\/span>runtime_error<\/span>(<\/span>"\u5199\u5165\u6587\u4ef6\u5931\u8d25"<\/span>)<\/span>;<\/span> }<\/span>
\n\/\/ \u4e4b\u540e\u4ea4\u7ed9\u6790\u6784\u5173\u95ed，\u4e0d\u9700\u8981\u624b\u52a8 close()<\/span><\/p>\n

if (!out) \u7528\u7684\u662f std::basic_ios::operator bool，\u7b49\u4ef7\u4e8e !out.fail()\u3002\u8fd9\u4e00\u70b9\u5728\u4e0b\u4e00\u8282\u4f1a\u770b\u5230\u5b83\u7684\u5b8c\u6574\u542b\u4e49\u3002<\/p>\n

6. \u72b6\u6001\u4f4d\u7684\u8bed\u4e49：good \/ eof \/ fail \/ bad<\/h3>\n

\u56db\u4e2a\u72b6\u6001\u4f4d\u90fd\u5728 std::ios_base \u91cc，\u4efb\u4f55\u4e00\u4e2a\u6d41\u5bf9\u8c61\u90fd\u80fd\u67e5：<\/p>\n

\u56db\u4e2a\u72b6\u6001\u4f4d（iostate）\u4e0e\u5b83\u4eec\u7684\u5173\u7cfb<\/p>\n

\u4e00\u5207\u6b63\u5e38 \u683c\u5f0f\u5316\u64cd\u4f5c\u5931\u8d25
\n +———–+ \u64cd\u4f5c\u5931\u8d25 +—————————+
\n | goodbit | ————–> | failbit |
\n | good()=T | <————– | fail()=true |
\n +———–+ clear() | (\u7c7b\u578b\u4e0d\u5339\u914d \/ \u6253\u5f00\u5931\u8d25) |
\n | +—————————+
\n | \u8bfb\u5230\u6587\u4ef6\u672b\u5c3e ^
\n v | \u5e95\u5c42\u8bbe\u5907\u51fa\u9519
\n +———–+ clear() +—————————+
\n | eofbit | | badbit |
\n | eof()=T | | bad()=true |
\n +———–+ | (\u6d41\u5df2\u4e0d\u53ef\u7528，\u522b\u518d\u7528\u5b83) |
\n +—————————+<\/p>\n

\u4e09\u53e5\u5224\u636e：
\n good() <=> state == 0 \u6700\u4e25\u683c，\u4e00\u70b9\u95ee\u9898\u90fd\u4e0d\u80fd\u6709
\n fail() <=> failbit | badbit \u300c\u8fd9\u6b21\u64cd\u4f5c\u6ca1\u6210\u529f\u300d，\u8fd9\u624d\u662f\u4e3b\u5224\u636e
\n !stream <=> fail() \u6240\u4ee5 while (in >> x) \u80fd\u540c\u65f6\u6321\u4f4f
\n \u6587\u4ef6\u8bfb\u5b8c（eofbit+failbit）\u548c\u683c\u5f0f\u9519\u8bef<\/p>\n

\u6709\u4e00\u4e2a\u6d41\u4f20\u5f88\u5e7f\u7684\u9519\u8bef\u5199\u6cd5\u662f while (!in.eof()) { getline(in, line); … }：\u5b83\u603b\u4f1a\u591a\u5904\u7406\u4e00\u6b21\u6700\u540e\u4e00\u884c，\u56e0\u4e3a eof() \u53ea\u6709\u5728\u300c\u5df2\u7ecf\u5c1d\u8bd5\u8bfb\u8fc7\u5e76\u649e\u4e0a\u672b\u5c3e\u300d\u4e4b\u540e\u624d\u4e3a\u771f\u3002\u6b63\u786e\u7684\u5faa\u73af\u6761\u4ef6\u662f\u76f4\u63a5\u7528 getline \u7684\u8fd4\u56de\u503c（\u8fd9\u7bc7\u6240\u6709\u793a\u4f8b\u90fd\u662f\u8fd9\u4e48\u5199\u7684）\u3002\u4e0b\u9762\u8fd9\u4e2a\u7a0b\u5e8f\u628a\u72b6\u6001\u4f4d\u7684\u5b9e\u9645\u53d6\u503c\u8dd1\u51fa\u6765：<\/p>\n

\/\/ file_state.cpp \u2014 \u7f16\u8bd1: g++ -std=c++17 -Wall -O2 file_state.cpp -o demo<\/span>
\n#<\/span>include<\/span> <fstream><\/span><\/span>
\n#<\/span>include<\/span> <iostream><\/span><\/span>
\n#<\/span>include<\/span> <string><\/span><\/span><\/p>\n

constexpr<\/span> const<\/span> char<\/span>*<\/span> kMissing =<\/span> "miao_tmp_no_such_file.txt"<\/span>;<\/span><\/p>\n

int<\/span> main<\/span>(<\/span>)<\/span> {<\/span>
\n std::<\/span>cout <<<\/span> std::<\/span>boolalpha;<\/span><\/p>\n

std::<\/span>ifstream lenient<\/span>(<\/span>kMissing)<\/span>;<\/span> \/\/ \u6587\u4ef6\u4e0d\u5b58\u5728<\/span>
\n std::<\/span>cout <<<\/span> "\u9ed8\u8ba4: is_open="<\/span> <<<\/span> lenient.<\/span>is_open<\/span>(<\/span>)<\/span> <<<\/span> " fail="<\/span> <<<\/span> lenient.<\/span>fail<\/span>(<\/span>)<\/span>
\n <<<\/span> " bad="<\/span> <<<\/span> lenient.<\/span>bad<\/span>(<\/span>)<\/span> <<<\/span> " eof="<\/span> <<<\/span> lenient.<\/span>eof<\/span>(<\/span>)<\/span>
\n <<<\/span> " good="<\/span> <<<\/span> lenient.<\/span>good<\/span>(<\/span>)<\/span> <<<\/span> '\\\\n'<\/span>;<\/span>
\n std::<\/span>string line;<\/span>
\n const<\/span> bool<\/span> got =<\/span> static_cast<\/span><<\/span>bool<\/span>><\/span><\/span><\/span>(<\/span>std::<\/span>getline<\/span>(<\/span>lenient,<\/span> line)<\/span>)<\/span>;<\/span>
\n std::<\/span>cout <<<\/span> "getline \u8fd4\u56de "<\/span> <<<\/span> got <<<\/span> "，line=["<\/span> <<<\/span> line <<<\/span> "]\\\\n"<\/span>;<\/span>
\n std::<\/span>cout <<<\/span> "\u4e4b\u540e\u518d\u67e5: eof="<\/span> <<<\/span> lenient.<\/span>eof<\/span>(<\/span>)<\/span> <<<\/span> " fail="<\/span> <<<\/span> lenient.<\/span>fail<\/span>(<\/span>)<\/span> <<<\/span> '\\\\n'<\/span>;<\/span><\/p>\n

try<\/span> {<\/span>
\n std::<\/span>ifstream strict;<\/span>
\n strict.<\/span>exceptions<\/span>(<\/span>std::<\/span>ios::<\/span>failbit |<\/span> std::<\/span>ios::<\/span>badbit)<\/span>;<\/span> \/\/ \u6253\u5f00\u5931\u8d25\u8981\u629b<\/span>
\n strict.<\/span>open<\/span>(<\/span>kMissing)<\/span>;<\/span>
\n }<\/span> catch<\/span> (<\/span>const<\/span> std::<\/span>ios_base::<\/span>failure&<\/span> e)<\/span> {<\/span>
\n std::<\/span>cout <<<\/span> "\u6355\u83b7\u5f02\u5e38: "<\/span> <<<\/span> e.<\/span>what<\/span>(<\/span>)<\/span> <<<\/span> '\\\\n'<\/span>;<\/span>
\n }<\/span>
\n std::<\/span>remove<\/span>(<\/span>kMissing)<\/span>;<\/span>
\n}<\/span><\/p>\n

\u9ed8\u8ba4: is_open=false fail=true bad=false eof=false good=false
\ngetline \u8fd4\u56de false，line=[]
\n\u4e4b\u540e\u518d\u67e5: eof=false fail=true
\n\u6355\u83b7\u5f02\u5e38: basic_ios::clear: iostream error<\/p>\n

\u8f93\u51fa\u628a\u4e24\u4ef6\u4e8b\u9489\u6b7b\u4e86：\u6587\u4ef6\u6253\u4e0d\u5f00\u65f6\u662f failbit \u800c\u4e0d\u662f eofbit（eof=false），\u5e76\u4e14 getline \u8fd4\u56de false \u65f6\u4e0d\u4f1a\u53bb\u52a8 line（\u4fdd\u6301\u7a7a\u4e32）\u3002\u6240\u4ee5\u300c\u8bfb\u5931\u8d25\u4f46\u7528\u4e86\u810f\u6570\u636e\u300d\u8fd9\u79cd bug，\u53ea\u8981\u68c0\u67e5\u8fd4\u56de\u503c\u5c31\u80fd\u62e6\u4f4f\u3002\u7b2c\u4e8c\u6bb5\u6f14\u793a exceptions()：\u6253\u5f00\u5b83\u4f1a\u628a\u8fd9\u4e9b\u72b6\u6001\u4f4d\u53d8\u6210\u5f02\u5e38，\u5931\u8d25\u5f53\u573a\u629b，\u4e0d\u7528\u7b49\u5230\u4e0b\u4e00\u6b21\u68c0\u67e5\u3002<\/p>\n

\u90a3\u5230\u5e95\u8be5\u7528\u54ea\u79cd？\u770b\u573a\u666f：<\/p>\n\n\u505a\u6cd5\u5931\u8d25\u65f6\u7684\u8868\u73b0\u9002\u5408<\/tr>\n\n\n\n\n
\u9ed8\u8ba4（\u4e0d\u629b）<\/td>\n\u9759\u9ed8\u7f6e\u4f4d，\u5fc5\u987b\u624b\u52a8 if (!in)<\/td>\n\u9010\u884c\u8bfb\u65e5\u5fd7\u3001\u80fd\u5bb9\u5fcd\u90e8\u5206\u5931\u8d25<\/td>\n<\/tr>\n
exceptions(failbit|badbit)<\/td>\n\u5f53\u573a\u629b std::ios_base::failure<\/td>\n\u914d\u7f6e\/\u6570\u636e\u6587\u4ef6\u5fc5\u987b\u5b8c\u6574\u8bfb\u5230，\u5b81\u53ef\u5feb\u5931\u8d25<\/td>\n<\/tr>\n
\u53ea\u5f00 badbit<\/td>\n\u53ea\u6709\u5e95\u5c42\u8bbe\u5907\u51fa\u9519\u624d\u629b<\/td>\n\u60f3\u4fdd\u7559\u300c\u8bfb\u5230 EOF \u662f\u6b63\u5e38\u7684\u300d\u8bed\u4e49<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

\u5b98\u65b9\u6587\u6863：std::basic_ios::rdstate \u4e0e\u72b6\u6001\u4f4d\u3001std::basic_ios::exceptions<\/p>\n

7. \u4e8c\u8fdb\u5236\u8bfb\u5199：write \/ read \u4e0e reinterpret_cast<\/h3>\n

\u6587\u672c\u6a21\u5f0f\u9002\u5408\u4eba\u770b，\u4e8c\u8fdb\u5236\u6a21\u5f0f\u9002\u5408\u628a\u5185\u5b58\u91cc\u7684\u6570\u636e\u6574\u5757\u642c\u8d70\u3002write \/ read \u7684\u7b7e\u540d\u90fd\u53ea\u8ba4 char \u6307\u9488，\u6240\u4ee5\u5fc5\u987b\u6362\u4e00\u6b21\u300c\u89c6\u89d2\u300d：<\/p>\n

std::vector<int> data{1, 2, 3, 2147483647} \u7684 16 \u4e2a\u5b57\u8282（\u5c0f\u7aef\u673a）<\/p>\n

01 00 00 00 | 02 00 00 00 | 03 00 00 00 | FF FF FF 7F
\n |– int 1 –|– int 2 –|– int 3 –|– int 2147483647 -|
\n ^
\n data.data() \u5c31\u662f\u8fd9\u6bb5\u8fde\u7eed\u5185\u5b58\u7684\u9996\u5b57\u8282\u5730\u5740<\/p>\n

\u4e3a\u4ec0\u4e48\u8981 reinterpret_cast<const char*>：
\n write() \u7684\u5f62\u53c2\u7c7b\u578b\u662f const char*，\u800c\u4f60\u624b\u4e0a\u662f int*
\n \u6807\u51c6\u89c4\u5b9a char \/ unsigned char \/ std::byte \u53ef\u4ee5\u300c\u522b\u540d\u300d\u4efb\u4f55\u5bf9\u8c61，
\n \u6240\u4ee5\u7528 char* \u53bb\u8bfb\u8fd9\u6bb5\u5b57\u8282\u662f\u5408\u6cd5\u7684；reinterpret_cast \u8868\u8fbe\u7684\u6b63\u662f
\n \u300c\u4e0d\u6539\u53d8\u4f4d\u6a21\u5f0f，\u53ea\u6362\u4e2a\u7c7b\u578b\u53bb\u770b\u5b83\u300d\u2014\u2014 \u5b83\u4e0d\u505a\u4efb\u4f55\u6570\u503c\u8f6c\u6362
\n \u8fd9\u662f reinterpret_cast \u5c11\u6709\u7684\u6b63\u5f53\u573a\u666f\u4e4b\u4e00（\u4e0d\u662f\u7c7b\u578b\u8f6c\u6362，\u662f\u91cd\u65b0\u89e3\u91ca）<\/p>\n

\/\/ file_binary.cpp \u2014 \u7f16\u8bd1: g++ -std=c++17 -Wall -O2 file_binary.cpp -o demo<\/span>
\n#<\/span>include<\/span> <cstdio><\/span><\/span>
\n#<\/span>include<\/span> <fstream><\/span><\/span>
\n#<\/span>include<\/span> <iostream><\/span><\/span>
\n#<\/span>include<\/span> <vector><\/span><\/span><\/p>\n

constexpr<\/span> const<\/span> char<\/span>*<\/span> kBinPath =<\/span> "miao_tmp_bin.dat"<\/span>;<\/span><\/p>\n

int<\/span> main<\/span>(<\/span>)<\/span> {<\/span>
\n const<\/span> std::<\/span>vector<<\/span>int<\/span>><\/span> data{<\/span>1<\/span>,<\/span> 2<\/span>,<\/span> 3<\/span>,<\/span> 2147483647<\/span>}<\/span>;<\/span>
\n {<\/span>
\n std::<\/span>ofstream out<\/span>(<\/span>kBinPath,<\/span> std::<\/span>ios::<\/span>out |<\/span> std::<\/span>ios::<\/span>binary |<\/span> std::<\/span>ios::<\/span>trunc)<\/span>;<\/span>
\n out.<\/span>write<\/span>(<\/span>reinterpret_cast<\/span><<\/span>const<\/span> char<\/span>*<\/span>><\/span><\/span><\/span>(<\/span>data.<\/span>data<\/span>(<\/span>)<\/span>)<\/span>,<\/span>
\n static_cast<\/span><<\/span>std::<\/span>streamsize><\/span><\/span><\/span>(<\/span>data.<\/span>size<\/span>(<\/span>)<\/span> *<\/span> sizeof<\/span>(<\/span>int<\/span>)<\/span>)<\/span>)<\/span>;<\/span>
\n }<\/span>
\n std::<\/span>ifstream probe<\/span>(<\/span>kBinPath,<\/span> std::<\/span>ios::<\/span>in |<\/span> std::<\/span>ios::<\/span>binary |<\/span> std::<\/span>ios::<\/span>ate)<\/span>;<\/span>
\n std::<\/span>cout <<<\/span> "\u6587\u4ef6\u5b57\u8282\u6570: "<\/span> <<<\/span> probe.<\/span>tellg<\/span>(<\/span>)<\/span> <<<\/span> '\\\\n'<\/span>;<\/span><\/p>\n

std::<\/span>ifstream in<\/span>(<\/span>kBinPath,<\/span> std::<\/span>ios::<\/span>in |<\/span> std::<\/span>ios::<\/span>binary)<\/span>;<\/span>
\n std::<\/span>vector<<\/span>int<\/span>><\/span> back<\/span>(<\/span>data.<\/span>size<\/span>(<\/span>)<\/span>,<\/span> 0<\/span>)<\/span>;<\/span>
\n in.<\/span>read<\/span>(<\/span>reinterpret_cast<\/span><<\/span>char<\/span>*<\/span>><\/span><\/span><\/span>(<\/span>back.<\/span>data<\/span>(<\/span>)<\/span>)<\/span>,<\/span>
\n static_cast<\/span><<\/span>std::<\/span>streamsize><\/span><\/span><\/span>(<\/span>back.<\/span>size<\/span>(<\/span>)<\/span> *<\/span> sizeof<\/span>(<\/span>int<\/span>)<\/span>)<\/span>)<\/span>;<\/span>
\n std::<\/span>cout <<<\/span> "\u8bfb\u5165\u5b57\u8282\u6570: "<\/span> <<<\/span> in.<\/span>gcount<\/span>(<\/span>)<\/span> <<<\/span> '\\\\n'<\/span>;<\/span>
\n std::<\/span>cout <<<\/span> "\u8bfb\u5230\u5185\u5bb9 : "<\/span>;<\/span>
\n for<\/span> (<\/span>const<\/span> int<\/span> v :<\/span> back)<\/span> {<\/span> std::<\/span>cout <<<\/span> v <<<\/span> ' '<\/span>;<\/span> }<\/span>
\n std::<\/span>cout <<<\/span> '\\\\n'<\/span>;<\/span>
\n std::<\/span>remove<\/span>(<\/span>kBinPath)<\/span>;<\/span>
\n}<\/span><\/p>\n

\u6587\u4ef6\u5b57\u8282\u6570: 16
\n\u8bfb\u5165\u5b57\u8282\u6570: 16
\n\u8bfb\u5230\u5185\u5bb9 : 1 2 3 2147483647 <\/p>\n

\u4e09\u4e2a\u7ec6\u8282：std::ios::ate \u8ba9\u6587\u4ef6\u4e00\u6253\u5f00\u5c31\u5b9a\u4f4d\u5230\u672b\u5c3e，\u6240\u4ee5 tellg() \u76f4\u63a5\u5c31\u662f\u6587\u4ef6\u5927\u5c0f，\u4e0d\u7528 seek \u4e24\u6b21；read \u4e4b\u540e\u7528 gcount() \u770b\u5b9e\u9645\u8bfb\u5230\u4e86\u591a\u5c11\u5b57\u8282，\u77ed\u8bfb（\u6587\u4ef6\u88ab\u622a\u65ad）\u65f6\u5b83\u5c0f\u4e8e\u8bf7\u6c42\u503c，\u8fd9\u662f\u5224\u65ad\u300c\u8bfb\u5168\u4e86\u6ca1\u300d\u7684\u6807\u51c6\u624b\u6bb5；\u6700\u540e，\u4e8c\u8fdb\u5236\u8de8\u5e73\u53f0\u53ea\u4fdd\u8bc1\u540c\u4e00\u5e73\u53f0\u540c\u4e00\u6b21\u7f16\u8bd1\u4e4b\u95f4\u53ef\u8bfb，\u5b57\u8282\u5e8f\u548c sizeof(int) \u4e00\u53d8\u5c31\u5e9f，\u771f\u8981\u957f\u671f\u5b58\u50a8\u5f97\u7528\u56fa\u5b9a\u5bbd\u5ea6\u7c7b\u578b（std::int32_t）\u5e76\u7ea6\u5b9a\u5b57\u8282\u5e8f\u3002<\/p>\n

\u5b98\u65b9\u6587\u6863：std::basic_ostream::write\u3001std::basic_istream::read<\/p>\n

8. \u7528 <filesystem> \u505a\u8def\u5f84\u4e0e\u6587\u4ef6\u5224\u65ad（C++17）<\/h3>\n

\u5728\u6253\u5f00\u6587\u4ef6\u4e4b\u524d\u5148\u95ee\u4e00\u53e5\u300c\u5b83\u5728\u4e0d\u5728\u3001\u662f\u4e0d\u662f\u666e\u901a\u6587\u4ef6\u300d，\u6bd4\u6253\u5f00\u5931\u8d25\u518d\u731c\u8981\u76f4\u767d\u5f97\u591a\u3002<filesystem> \u4ece C++17 \u8d77\u8fdb\u6807\u51c6\u5e93，gcc 9 \u4e4b\u540e\u4e0d\u9700\u8981\u989d\u5916\u94fe\u63a5 -lstdc++fs：<\/p>\n

\/\/ file_fs.cpp \u2014 \u7f16\u8bd1: g++ -std=c++17 -Wall -O2 file_fs.cpp -o demo<\/span>
\n#<\/span>include<\/span> <filesystem><\/span><\/span>
\n#<\/span>include<\/span> <fstream><\/span><\/span>
\n#<\/span>include<\/span> <iostream><\/span><\/span><\/p>\n

namespace<\/span> fs =<\/span> std::<\/span>filesystem;<\/span><\/p>\n

int<\/span> main<\/span>(<\/span>)<\/span> {<\/span>
\n const<\/span> fs::<\/span>path p =<\/span> "miao_tmp_fs_probe.txt"<\/span>;<\/span>
\n {<\/span>
\n std::<\/span>ofstream f<\/span>(<\/span>p)<\/span>;<\/span>
\n f <<<\/span> "xy\\\\n"<\/span>;<\/span>
\n }<\/span>
\n std::<\/span>cout <<<\/span> std::<\/span>boolalpha;<\/span>
\n std::<\/span>cout <<<\/span> "exists : "<\/span> <<<\/span> fs::<\/span>exists<\/span>(<\/span>p)<\/span> <<<\/span> '\\\\n'<\/span>;<\/span>
\n std::<\/span>cout <<<\/span> "regular : "<\/span> <<<\/span> fs::<\/span>is_regular_file<\/span>(<\/span>p)<\/span> <<<\/span> '\\\\n'<\/span>;<\/span>
\n std::<\/span>cout <<<\/span> "extension : "<\/span> <<<\/span> p.<\/span>extension<\/span>(<\/span>)<\/span>.<\/span>string<\/span>(<\/span>)<\/span> <<<\/span> '\\\\n'<\/span>;<\/span>
\n std::<\/span>cout <<<\/span> "stem : "<\/span> <<<\/span> p.<\/span>stem<\/span>(<\/span>)<\/span>.<\/span>string<\/span>(<\/span>)<\/span> <<<\/span> '\\\\n'<\/span>;<\/span>
\n std::<\/span>cout <<<\/span> "file_size : "<\/span> <<<\/span> fs::<\/span>file_size<\/span>(<\/span>p)<\/span> <<<\/span> '\\\\n'<\/span>;<\/span>
\n std::<\/span>cout <<<\/span> "remove \u8fd4\u56de : "<\/span> <<<\/span> fs::<\/span>remove<\/span>(<\/span>p)<\/span> <<<\/span> '\\\\n'<\/span>;<\/span>
\n std::<\/span>cout <<<\/span> "\u5220\u540e exists : "<\/span> <<<\/span> fs::<\/span>exists<\/span>(<\/span>p)<\/span> <<<\/span> '\\\\n'<\/span>;<\/span>
\n}<\/span><\/p>\n

exists : true
\nregular : true
\nextension : .txt
\nstem : miao_tmp_fs_probe
\nfile_size : 3
\nremove \u8fd4\u56de : true
\n\u5220\u540e exists : false<\/p>\n

\u8981\u6ce8\u610f fs::exists(p) \u8fd9\u7c7b\u67e5\u8be2\u9ed8\u8ba4\u4e0d\u629b\u5f02\u5e38，\u8fd4\u56de false \u5c31\u4ee3\u8868\u300c\u4e0d\u5b58\u5728\u6216\u8005\u67e5\u4e0d\u4e86\u300d；\u60f3\u8ba9\u5b83\u629b，\u5f97\u4f20 std::error_code \u7684\u91cd\u8f7d\u6216\u8005\u7528 fs::directory_entry\u3002\u53e6\u5916 fs::remove \u8fd4\u56de bool（\u662f\u5426\u771f\u7684\u5220\u6389\u4e86），\u5220\u4e0d\u5b58\u5728\u7684\u6587\u4ef6\u662f false \u800c\u4e0d\u662f\u9519\u8bef\u3002<\/p>\n

\u5b98\u65b9\u6587\u6863：std::filesystem<\/p>\n

9. \u5b8c\u6574\u793a\u4f8b：\u5199\u914d\u7f6e \u2192 \u8bfb\u56de\u6765 \u2192 \u6821\u9a8c<\/h3>\n

\u628a\u8fd9\u7bc7\u6240\u6709\u8981\u70b9\u4e32\u6210\u4e00\u4e2a\u80fd\u6574\u4f53\u8dd1\u7684\u7a0b\u5e8f：ofstream \u8986\u76d6\u5199\u3001\u5199\u5b8c\u68c0\u67e5\u72b6\u6001\u3001ifstream \u9010\u884c getline\u3001\u952e\u503c\u5bf9\u89e3\u6790\u3001\u5931\u8d25\u65f6\u7528 std::optional \u8868\u8fbe\u300c\u6ca1\u6709\u503c\u300d\u800c\u4e0d\u662f\u9760\u54e8\u5175\u503c\u3002<\/p>\n

\/\/ file_config.cpp \u2014 \u7f16\u8bd1: g++ -std=c++17 -Wall -O2 file_config.cpp -o demo<\/span>
\n#<\/span>include<\/span> <cstdio><\/span><\/span>
\n#<\/span>include<\/span> <fstream><\/span><\/span>
\n#<\/span>include<\/span> <iostream><\/span><\/span>
\n#<\/span>include<\/span> <optional><\/span><\/span>
\n#<\/span>include<\/span> <string><\/span><\/span><\/p>\n

constexpr<\/span> const<\/span> char<\/span>*<\/span> kConfigPath =<\/span> "miao_tmp_app.conf"<\/span>;<\/span><\/p>\n

struct<\/span> Config<\/span> {<\/span>
\n int<\/span> width =<\/span> 0<\/span>;<\/span>
\n int<\/span> height =<\/span> 0<\/span>;<\/span>
\n std::<\/span>string name;<\/span>
\n}<\/span>;<\/span><\/p>\n

bool<\/span> save<\/span>(<\/span>const<\/span> Config&<\/span> c,<\/span> const<\/span> char<\/span>*<\/span> path)<\/span> {<\/span>
\n std::<\/span>ofstream out<\/span>(<\/span>path,<\/span> std::<\/span>ios::<\/span>out |<\/span> std::<\/span>ios::<\/span>trunc)<\/span>;<\/span>
\n if<\/span> (<\/span>!<\/span>out)<\/span> {<\/span> return<\/span> false<\/span>;<\/span> }<\/span>
\n out <<<\/span> "width="<\/span> <<<\/span> c.<\/span>width <<<\/span> '\\\\n'<\/span>
\n <<<\/span> "height="<\/span> <<<\/span> c.<\/span>height <<<\/span> '\\\\n'<\/span>
\n <<<\/span> "name="<\/span> <<<\/span> c.<\/span>name <<<\/span> '\\\\n'<\/span>;<\/span>
\n out.<\/span>flush<\/span>(<\/span>)<\/span>;<\/span>
\n return<\/span> static_cast<\/span><<\/span>bool<\/span>><\/span><\/span><\/span>(<\/span>out)<\/span>;<\/span> \/\/ \u5199\u5b8c\u7acb\u523b\u67e5，\u4e0d\u9760\u6790\u6784<\/span>
\n}<\/span><\/p>\n

std::<\/span>optional<<\/span>Config><\/span> load<\/span>(<\/span>const<\/span> char<\/span>*<\/span> path)<\/span> {<\/span>
\n std::<\/span>ifstream in<\/span>(<\/span>path)<\/span>;<\/span>
\n if<\/span> (<\/span>!<\/span>in)<\/span> {<\/span> return<\/span> std::<\/span>nullopt;<\/span> }<\/span> \/\/ \u6587\u4ef6\u6253\u4e0d\u5f00：\u660e\u786e\u8868\u8fbe\u300c\u6ca1\u6709\u503c\u300d<\/span>
\n Config c;<\/span>
\n std::<\/span>string line;<\/span>
\n while<\/span> (<\/span>std::<\/span>getline<\/span>(<\/span>in,<\/span> line)<\/span>)<\/span> {<\/span>
\n const<\/span> std::<\/span>size_t pos =<\/span> line.<\/span>find<\/span>(<\/span>'='<\/span>)<\/span>;<\/span>
\n if<\/span> (<\/span>pos ==<\/span> std::<\/span>string::<\/span>npos)<\/span> {<\/span> continue<\/span>;<\/span> }<\/span> \/\/ \u7a7a\u884c\u3001\u6ce8\u91ca\u884c\u76f4\u63a5\u8df3\u8fc7<\/span>
\n const<\/span> std::<\/span>string key =<\/span> line.<\/span>substr<\/span>(<\/span>0<\/span>,<\/span> pos)<\/span>;<\/span>
\n const<\/span> std::<\/span>string val =<\/span> line.<\/span>substr<\/span>(<\/span>pos +<\/span> 1<\/span>)<\/span>;<\/span>
\n if<\/span> (<\/span>key ==<\/span> "width"<\/span>)<\/span> {<\/span> c.<\/span>width =<\/span> std::<\/span>stoi<\/span>(<\/span>val)<\/span>;<\/span> }<\/span>
\n if<\/span> (<\/span>key ==<\/span> "height"<\/span>)<\/span> {<\/span> c.<\/span>height =<\/span> std::<\/span>stoi<\/span>(<\/span>val)<\/span>;<\/span> }<\/span>
\n if<\/span> (<\/span>key ==<\/span> "name"<\/span>)<\/span> {<\/span> c.<\/span>name =<\/span> val;<\/span> }<\/span>
\n }<\/span>
\n return<\/span> c;<\/span>
\n}<\/span><\/p>\n

int<\/span> main<\/span>(<\/span>)<\/span> {<\/span>
\n const<\/span> Config written{<\/span>1920<\/span>,<\/span> 1080<\/span>,<\/span> "miao"<\/span>}<\/span>;<\/span>
\n if<\/span> (<\/span>!<\/span>save<\/span>(<\/span>written,<\/span> kConfigPath)<\/span>)<\/span> {<\/span>
\n std::<\/span>cerr <<<\/span> "\u5199\u914d\u7f6e\u5931\u8d25\\\\n"<\/span>;<\/span>
\n return<\/span> 1<\/span>;<\/span>
\n }<\/span><\/p>\n

std::<\/span>ifstream show<\/span>(<\/span>kConfigPath)<\/span>;<\/span>
\n std::<\/span>string line;<\/span>
\n while<\/span> (<\/span>std::<\/span>getline<\/span>(<\/span>show,<\/span> line)<\/span>)<\/span> {<\/span> std::<\/span>cout <<<\/span> "\u6587\u4ef6\u5185\u5bb9| "<\/span> <<<\/span> line <<<\/span> '\\\\n'<\/span>;<\/span> }<\/span><\/p>\n

const<\/span> std::<\/span>optional<<\/span>Config><\/span> back =<\/span> load<\/span>(<\/span>kConfigPath)<\/span>;<\/span>
\n if<\/span> (<\/span>!<\/span>back)<\/span> {<\/span>
\n std::<\/span>cerr <<<\/span> "\u8bfb\u914d\u7f6e\u5931\u8d25\\\\n"<\/span>;<\/span>
\n return<\/span> 1<\/span>;<\/span>
\n }<\/span>
\n const<\/span> bool<\/span> same =<\/span> back-><\/span>width ==<\/span> written.<\/span>width
\n &&<\/span> back-><\/span>height ==<\/span> written.<\/span>height
\n &&<\/span> back-><\/span>name ==<\/span> written.<\/span>name;<\/span>
\n std::<\/span>cout <<<\/span> "\u8bfb\u56de width="<\/span> <<<\/span> back-><\/span>width
\n <<<\/span> " height="<\/span> <<<\/span> back-><\/span>height
\n <<<\/span> " name="<\/span> <<<\/span> back-><\/span>name <<<\/span> '\\\\n'<\/span>;<\/span>
\n std::<\/span>cout <<<\/span> "\u4e0e\u5199\u5165\u4e00\u81f4: "<\/span> <<<\/span> (<\/span>same ?<\/span> "true"<\/span> :<\/span> "false"<\/span>)<\/span> <<<\/span> '\\\\n'<\/span>;<\/span>
\n std::<\/span>remove<\/span>(<\/span>kConfigPath)<\/span>;<\/span>
\n}<\/span><\/p>\n

\u6587\u4ef6\u5185\u5bb9| width=1920
\n\u6587\u4ef6\u5185\u5bb9| height=1080
\n\u6587\u4ef6\u5185\u5bb9| name=miao
\n\u8bfb\u56de width=1920 height=1080 name=miao
\n\u4e0e\u5199\u5165\u4e00\u81f4: true<\/p>\n

\u8fd9\u4e2a\u7a0b\u5e8f\u5728\u4efb\u4f55\u76ee\u5f55\u3001\u8dd1\u591a\u5c11\u6b21\u7ed3\u679c\u90fd\u4e00\u6837：\u6587\u4ef6\u540d\u56fa\u5b9a\u4f46\u6bcf\u6b21\u90fd\u4ece trunc \u5f00\u59cb，\u7ed3\u675f\u65f6\u81ea\u5df1 remove \u6389，\u4e0d\u4f9d\u8d56\u4e0a\u4e00\u6b21\u8fd0\u884c\u7684\u6b8b\u7559\u3002<\/p>\n

10. \u5ef6\u4f38\u9605\u8bfb<\/h3>\n
    \n
  • std::basic_filebuf::open \u7684\u6a21\u5f0f\u8868 \u2014\u2014 \u6253\u5f00\u6a21\u5f0f\u7684\u6743\u5a01\u5b9a\u4e49，app \u9690\u542b out \u4e4b\u7c7b\u7684\u7ec6\u8282\u90fd\u5199\u5728\u8fd9\u91cc\u3002<\/li>\n
  • std::basic_ifstream \u2014\u2014 \u6784\u9020\u51fd\u6570\u4e0e open \u7684\u9ed8\u8ba4\u6a21\u5f0f\u3002<\/li>\n
  • std::basic_ios::rdstate \u2014\u2014 \u72b6\u6001\u4f4d\u4e0e good\/fail\/eof\/bad \u7684\u5bf9\u5e94\u5173\u7cfb\u3002<\/li>\n
  • std::basic_istream::getline \u2014\u2014 \u4e3a\u4ec0\u4e48\u5b83\u548c >> \u5bf9\u7a7a\u767d\u7684\u5904\u7406\u4e0d\u540c\u3002<\/li>\n
  • std::filesystem \u2014\u2014 \u8def\u5f84\u62fc\u63a5\u3001\u6587\u4ef6\u5224\u65ad\u3001\u76ee\u5f55\u904d\u5386\u90fd\u5728\u8fd9\u513f\u3002<\/li>\n<\/ul>\n

    \u672c\u77e5\u8bc6\u5e93\u5185\u7684\u76f8\u5173\u7bc7\u76ee：<\/p>\n

      \n
    • \u300aC++ stringstream \u5b9e\u7528\u6307\u5357：\u5206\u8bcd\u89e3\u6790\u3001\u7c7b\u578b\u4e92\u8f6c\u4e0e clear\/str \u7684\u533a\u522b\u300b \u2014\u2014 stringstream \u662f\u6807\u51c6\u5e93\u91cc\u7684\u300c\u5185\u5b58 IO\u300d\u4e09\u4ef6\u5957<\/li>\n
    • \u300aC++ iostream \u683c\u5f0f\u5316\u8f93\u51fa：setw \u4e00\u6b21\u6027\u3001fixed \u6301\u4e45，\u4e24\u4e2a\u5751\u4e00\u6b21\u5206\u6e05\u300b \u2014\u2014 iomanip \u7684\u64cd\u7eb5\u7b26\u771f\u6b63\u96be\u7684\u4e0d\u662f\u8bb0\u540d\u5b57，\u800c\u662f\u5206\u6e05\u8c01\u53ea\u5f71\u54cd\u4e0b\u4e00\u4e2a\u8f93\u51fa\u9879\u3001\u8c01\u4f1a\u4e00\u76f4\u7559\u5728\u6d41\u7684\u72b6\u6001\u91cc\u3002<\/li>\n
    • \u300aprintf \u4e0e cout \u7684\u6027\u80fd\u5dee\u5f02\u4e0e\u6df7\u7528\u9677\u9631：sync_with_stdio \u5230\u5e95\u662f\u4ec0\u4e48\u300b \u2014\u2014 printf \u4e0e cout \u7684\u6027\u80fd\u5dee\u5f02\u4e0e\u6df7\u7528\u9677\u9631，\u540c\u4f53\u7cfb\u91cc\u6700\u8be5\u4e00\u8d77\u770b\u7684\u53e6\u4e00\u7bc7\u3002<\/li>\n<\/ul>\n

      11. \u4e00\u53e5\u8bdd\u603b\u7ed3<\/h3>\n

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