the go blog defer panic recover code example

Example 1: the go blog defer panic recover

package main

import "fmt"

func main() {
    f()
    fmt.Println("Returned normally from f.")
}

func f() {
    defer func() {
        if r := recover(); r != nil {
            fmt.Println("Recovered in f", r)
        }
    }()
    fmt.Println("Calling g.")
    g(0)
    fmt.Println("Returned normally from g.")
}

func g(i int) {
    if i > 3 {
        fmt.Println("Panicking!")
        panic(fmt.Sprintf("%v", i))
    }
    defer fmt.Println("Defer in g", i)
    fmt.Println("Printing in g", i)
    g(i + 1)
}

Example 2: the go blog defer panic recover

func a() {
    i := 0
    defer fmt.Println(i)
    i++
    return
}

Example 3: the go blog defer panic recover

printHeader()
defer printFooter()

Example 4: the go blog defer panic recover

mu.Lock()
defer mu.Unlock()

Example 5: the go blog defer panic recover

func CopyFile(dstName, srcName string) (written int64, err error) {
    src, err := os.Open(srcName)
    if err != nil {
        return
    }

    dst, err := os.Create(dstName)
    if err != nil {
        return
    }

    written, err = io.Copy(dst, src)
    dst.Close()
    src.Close()
    return
}

Example 6: the go blog defer panic recover

Calling g.
Printing in g 0
Printing in g 1
Printing in g 2
Printing in g 3
Panicking!
Defer in g 3
Defer in g 2
Defer in g 1
Defer in g 0
panic: 4

panic PC=0x2a9cd8
[stack trace omitted]

Example 7: the go blog defer panic recover

Calling g.
Printing in g 0
Printing in g 1
Printing in g 2
Printing in g 3
Panicking!
Defer in g 3
Defer in g 2
Defer in g 1
Defer in g 0
Recovered in f 4
Returned normally from f.

Example 8: the go blog defer panic recover

func c() (i int) {
    defer func() { i++ }()
    return 1
}

Example 9: the go blog defer panic recover

func CopyFile(dstName, srcName string) (written int64, err error) {
    src, err := os.Open(srcName)
    if err != nil {
        return
    }
    defer src.Close()

    dst, err := os.Create(dstName)
    if err != nil {
        return
    }
    defer dst.Close()

    return io.Copy(dst, src)
}

Example 10: the go blog defer panic recover

func b() {
    for i := 0; i < 4; i++ {
        defer fmt.Print(i)
    }
}