Golang panic

在Go语言中，panic就像异常一样，它也是在运行时出现的。或者换句话说，恐慌是指在你的Go程序中出现了一个意外情况，由于这个原因，你的程序执行被终止了。如例1所示，有时恐慌是在运行时发生的，如越界数组访问等，有时是程序员故意抛出的，以处理Go程序中最坏的情况，如例2所示。

恐慌函数是一个内置的函数，定义在Go语言的内置包中。这个函数终止了控制流并开始恐慌。

语法

func panic(v interface{})

它可以接收任何类型的参数。当围棋程序发生慌乱时，程序会在运行时终止，并在输出屏幕上显示错误信息以及直到发生慌乱时的堆栈跟踪。一般来说，在Go语言中，当程序发生慌乱时，程序不会立即终止，而是在Go完成该程序的所有待定工作后终止。
例如，假设一个函数A调用了慌乱，那么函数A的执行就会停止，如果A中有任何延迟的函数，那么它们就会正常执行，然后函数A返回给它的调用者，对调用者来说，A的行为就像调用了慌乱。这个过程一直持续到当前goroutine中的所有函数被返回，之后程序崩溃，如例3所示。

例1 :

// Simple Go program which illustrates
// the concept of panic
package main
  
import "fmt"
  
// Main function
func main() {
  
    // Creating an array of string type
    // Using var keyword
    var myarr [3]string
  
    // Elements are assigned
    // using an index
    myarr[0] = "GFG"
    myarr[1] = "GeeksforGeeks"
    myarr[2] = "Geek"
  
    // Accessing the elements
    // of the array
    // Using index value
    fmt.Println("Elements of Array:")
    fmt.Println("Element 1: ", myarr[0])
  
    // Program panics because
    // the size of the array is
    // 3 and we try to access
    // index 5 which is not 
    // available in the current array,
    // So, it gives an runtime error
    fmt.Println("Element 2: ", myarr[5])
  
}

输出

./prog.go:32:34: invalid array index 5 (out of bounds for 3-element array)

例2 :

// Go program which illustrates 
// how to create your own panic
// Using panic function
package main
  
import "fmt"
  
// Function
func entry(lang *string, aname *string) {
  
    // When the value of lang 
    // is nil it will panic
    if lang == nil {
        panic("Error: Language cannot be nil")
    }
      
    // When the value of aname
    // is nil it will panic
    if aname == nil {
        panic("Error: Author name cannot be nil")
    }
  
    // When the values of the lang and aname 
    // are non-nil values it will print 
    // normal output
    fmt.Printf("Author Language: %s \n Author Name: %s\n", *lang, *aname)
}
  
// Main function
func main() {
  
    A_lang := "GO Language"
  
    // Here in entry function, we pass 
    // a non-nil and nil values
    // Due to nil value this method panics
    entry(&A_lang, nil)
}

输出

panic: Error: Author name cannot be nil

goroutine 1 [running]:
main.entry(0x41a788, 0x0)
    /tmp/sandbox108627012/prog.go:20 +0x140
main.main()
    /tmp/sandbox108627012/prog.go:37 +0x40

例3 :

// Go program which illustrates the
// concept of Defer while panicking
package main
  
import (
    "fmt"
)
  
// Function
func entry(lang *string, aname *string) {
  
    // Defer statement
    defer fmt.Println("Defer statement in the entry function")
  
    // When the value of lang
    // is nil it will panic
    if lang == nil {
        panic("Error: Language cannot be nil")
    }
      
    // When the value of aname
    // is nil it will panic
    if aname == nil {
        panic("Error: Author name cannot be nil")
    }
  
    // When the values of the lang and aname
    // are non-nil values it will 
    // print normal output
    fmt.Printf("Author Language: %s \n Author Name: %s\n", *lang, *aname)
}
  
// Main function
func main() {
  
    A_lang := "GO Language"
  
    // Defer statement
    defer fmt.Println("Defer statement in the Main function")
  
    // Here in entry function, we pass
    // one non-nil and one-nil value
    // Due to nil value this method panics
    entry(&A_lang, nil)
}

输出

Defer statement in the entry function
Defer statement in the Main function
panic: Error: Author name cannot be nil

goroutine 1 [running]:
main.entry(0x41a780, 0x0)
    /tmp/sandbox121565297/prog.go:24 +0x220
main.main()
    /tmp/sandbox121565297/prog.go:44 +0xa0