通过类型断言获取error类型，获得更详细的信息
package main
import (
"fmt"
"os"
)
func main() {
f, err := os.Open("/test.txt")
if err, ok := err.(*os.PathError); ok {
fmt.Println("File at path", err.Path, "failed to open")
return
}
fmt.Println(f.Name(), "opened successfully")
}