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eBook/18.7.md

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+# 18.7 文件
+
+（1）如何打开一个文件并读取：
+ 
+```go    
+file, err := os.Open("input.dat")
+  if err != nil {
+    fmt.Printf("An error occurred on opening the inputfile\n" +
+      "Does the file exist?\n" +
+      "Have you got acces to it?\n")
+    return
+  }
+  defer file.Close()
+  iReader := bufio.NewReader(file)
+  for {
+    str, err := iReader.ReadString('\n')
+    if err != nil {
+      return // error or EOF
+    }
+    fmt.Printf("The input was: %s", str)
+  }
+```
+
+（2）如何通过切片读写文件：
+    
+```go
+func cat(f *file.File) {
+  const NBUF = 512
+  var buf [NBUF]byte
+  for {
+    switch nr, er := f.Read(buf[:]); true {
+    case nr < 0:
+      fmt.Fprintf(os.Stderr, "cat: error reading from %s: %s\n",
+        f.String(), er.String())
+      os.Exit(1)
+    case nr == 0: // EOF
+      return
+    case nr > 0:
+      if nw, ew := file.Stdout.Write(buf[0:nr]); nw != nr {
+        fmt.Fprintf(os.Stderr, "cat: error writing from %s: %s\n",
+          f.String(), ew.String())
+      }
+    }
+  }
+}
+```
+
+## 链接
+
+- [目录](directory.md)
+- 上一章：[运算符模板和接口](17.4.md)
+- 下一节：[字符串](18.1.md)