defer, panic, recover使用总结

1. defer ： 延迟调用。多个defer，依次入栈，在函数即将退出时，依次出栈调用

 package main
 import "fmt"
 func main() {
     defer func() {
         fmt.Println("defer one")　　
     }()
     defer func() {
         fmt.Println("defer two")　　　
     }()
     defer func() {
         fmt.Println("defer three")　　
     }()
 }

2. panic和defer结合使用：panic触发错误，defer依次出栈调用，没有recover捕获的情况下，最后才打印错误

 package main
 import "fmt"
 func main() {
     defer func() {
         fmt.Println("defer one")
     }()
     defer func() {
         fmt.Println("defer two")
     }()
     defer func() {
         fmt.Println("defer three")
     }()
     panic("panic here")
 }

3. defer,panic, recover 结合使用，panic触发错误，defer依次出栈调用，直到被recover捕获，打印捕获的信息，之后继续defer出栈

例一:

 package main
 import "fmt"
 func main() {
     defer func() {
         fmt.Println("defer one")
     }()
     defer func() {
         fmt.Println("defer two")
     }()
     defer func() {
         if info := recover(); info != nil {
             fmt.Println("catch: ", info)
         }
         fmt.Println("defer three")
     }()
     panic("panic here")
 }

例二：

package main
import "fmt"
func main() {
    defer func() {
        fmt.Println("defer one")
    }()
    defer func() {
        if info := recover(); info != nil {
            fmt.Println("catch: ", info)
        }
        fmt.Println("defer two")
    }()
    defer func() {
        fmt.Println("defer three")
    }()
    panic("panic here")
}

例三：

package main
import "fmt"
func main() {
    defer func() {
        if info := recover(); info != nil {
            fmt.Println("catch: ", info)
        }
        fmt.Println("defer one")
    }()
    defer func() {
        fmt.Println("defer two")
    }()
    defer func() {
        fmt.Println("defer three")
    }()
    panic("panic here")
}

4. recover 必须在defer中调用，才有效，否则返回nil

package main
import "fmt"
func main() {
    if info := recover(); info != nil {
        fmt.Println("catch: ", info)
    } else {
        fmt.Println("recover return nil")
    }
    defer func() {
        fmt.Println("defer one")
    }()
    defer func() {
        fmt.Println("defer two")
    }()
    defer func() {
        fmt.Println("defer three")
    }()
    panic("panic here")
}

5. panic 其后的代码不会执行

例一：

package main
import "fmt"
func main() {
    defer func() {
        fmt.Println("defer one")
    }()
    defer func() {
        fmt.Println("defer two")
    }()
    defer func() {
        fmt.Println("defer three")
    }()
    panic("panic here")
    if info := recover(); info != nil {
        fmt.Println("catch: ", info)
    } else {
        fmt.Println("recover return nil")
    }
}

例二：

package main
import "fmt"
func main() {
    defer func() {
        fmt.Println("defer one")
    }()
    defer func() {
        if v := recover(); v != nil {
            fmt.Println("catch panic error: ", v)
        }
        fmt.Println("defer two")
    }()
    defer func() {
        fmt.Println("defer three")
    }()
    panic("panic here")
    fmt.Println("after panic")
}