The solution to golang bad file descriptor problem

Found the problem

In golang, the above error occurred while writing to a file. First of all, reproduce the problem.

package main

import (
 "os"
 "fmt"
)

func main() {
 file, err := os.Open("a.txt")
 if err != nil {
  fmt.Println(err)
 }
 defer file.Close()

 content:=[]byte("Go is an open source programing language that makes it easy to build simple,reliable,and efficient software")
 _, err = file.Write(content)
 if err != nil {
  fmt.Println(err)
 }
}

This will cause an error to run write a.txt: bad file descriptor . What is the reason? In fact this and os.Open() Functions are concerned, so let's look at the Open() function.

func Open(name string) (*File,error) {
 return OpenFile(name, O_RDONLY, 0)
}

As you can see, the default mode for the Open function to open a file is read-only, so you are not allowed to write to an open file. The value of the second parameter passed into the OpenFile function can be:

Parameter name meaning
O_RDONLY opens the read-only file
O_WRONLY opens write only files
O_RDWR opens to read and write files
O_APPEND appends data to the end of the file when it writes to it
O_CREATE Creates a new file if one does not exist
The O_EXCL file must not exist, and then a new file is created
O_SYNC turns on synchronization I/0
The O_TRUNC file can be truncated when opened

The solution

Now that we know why, the solution is simply to change the way the file is read. The following cases:

package main

import (
 "os"
 "fmt"
)

func main() {
 file, err := os.OpenFile("a.txt", os.O_APPEND|os.O_WRONLY, os.ModeAppend)
 if err != nil {
  fmt.Println(err)
 }
 defer file.Close()

 content:=[]byte("Go is an open source programing language that makes it easy to build simple,reliable,and efficient software")
 _, err = file.Write(content)
 if err != nil {
  fmt.Println(err)
 }
}

conclusion