defer, panic, recover使用总结

Posted 2021-12-07 bluepegasus

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

 1 package main
 2 import "fmt"
 3 func main() {
 4     defer func() {
 5         fmt.Println("defer one")　　 
 6     }()
 7     defer func() {
 8         fmt.Println("defer two")　　　
 9     }()
10     defer func() {
11         fmt.Println("defer three")　　
12     }()
13 }

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

 1 package main
 2 import "fmt"
 3 func main() {
 4     defer func() {
 5         fmt.Println("defer one")
 6     }()
 7     defer func() {
 8         fmt.Println("defer two")
 9     }()
10     defer func() {
11         fmt.Println("defer three")
12     }()
13     panic("panic here")
14 }

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:

 1 package main
 2 import "fmt"
 3 func main() {
 4     defer func() {
 5         fmt.Println("defer one")
 6     }()
 7     defer func() {
 8         fmt.Println("defer two")
 9     }()
10     defer func() {
11         if info := recover(); info != nil {
12             fmt.Println("catch: ", info)
13         }
14         fmt.Println("defer three")
15     }()
16     panic("panic here")
17 }

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")
}