Error Handling Go Language
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Mailing List Go on Google+ Go+ Community Go on Twitter Blog index The Go Blog Error handling and Go 12 July 2011 error handling in c language Introduction If you have written any Go code you have probably encountered
Go Lang Error Handling
the built-in error type. Go code uses error values to indicate an abnormal state. For example, the os.Open function go error handling verbose returns a non-nil error value when it fails to open a file. func Open(name string) (file *File, err error) The following code uses os.Open to open a file. If an go error handling patterns error occurs it calls log.Fatal to print the error message and stop. f, err := os.Open("filename.ext") if err != nil { log.Fatal(err) } // do something with the open *File f You can get a lot done in Go knowing just this about the error type, but in this article we'll take a closer look at error and discuss some good practices
Error Handling C Programming
for error handling in Go. The error type The error type is an interface type. An error variable represents any value that can describe itself as a string. Here is the interface's declaration: type error interface { Error() string } The error type, as with all built in types, is predeclared in the universe block. The most commonly-used error implementation is the errors package's unexported errorString type. // errorString is a trivial implementation of error. type errorString struct { s string } func (e *errorString) Error() string { return e.s } You can construct one of these values with the errors.New function. It takes a string that it converts to an errors.errorString and returns as an error value. // New returns an error that formats as the given text. func New(text string) error { return &errorString{text} } Here's how you might use errors.New: func Sqrt(f float64) (float64, error) { if f < 0 { return 0, errors.New("math: square root of negative number") } // implementation } A caller passing a negative argument to Sqrt receives a non-nil error value (whose concrete representati
in C. Go’s approach makes it easy to see which functions return errors and to handle them using the same language constructs employed for any other, non-error tasks. package main import "errors" import error handling visual basic "fmt" By convention, errors are the last return value and have type error, a error handling java built-in interface. func f1(arg int) (int, error) { if arg == 42 { errors.New constructs a basic error value with the
Error Handling Perl
given error message. return -1, errors.New("can't work with 42") } A nil value in the error position indicates that there was no error. return arg + 3, nil } It’s possible to use custom types https://blog.golang.org/error-handling-and-go as errors by implementing the Error() method on them. Here’s a variant on the example above that uses a custom type to explicitly represent an argument error. type argError struct { arg int prob string } func (e *argError) Error() string { return fmt.Sprintf("%d - %s", e.arg, e.prob) } func f2(arg int) (int, error) { if arg == 42 { In this case we use &argError syntax to build a new https://gobyexample.com/errors struct, supplying values for the two fields arg and prob. return -1, &argError{arg, "can't work with it"} } return arg + 3, nil } func main() { The two loops below test out each of our error-returning functions. Note that the use of an inline error check on the if line is a common idiom in Go code. for _, i := range []int{7, 42} { if r, e := f1(i); e != nil { fmt.Println("f1 failed:", e) } else { fmt.Println("f1 worked:", r) } } for _, i := range []int{7, 42} { if r, e := f2(i); e != nil { fmt.Println("f2 failed:", e) } else { fmt.Println("f2 worked:", r) } } If you want to programmatically use the data in a custom error, you’ll need to get the error as an instance of the custom error type via type assertion. _, e := f2(42) if ae, ok := e.(*argError); ok { fmt.Println(ae.arg) fmt.Println(ae.prob) } } $ go run errors.go f1 worked: 10 f1 failed: can't work with 42 f2 worked: 10 f2 failed: 42 - can't work with it 42 can't work with it See this great post on the Go blog for more on error handling. Next example: Goroutines. by @mmcgrana | feedback | source | license
ServerSitemap The Authorryannedolan.info Recent site activityHomeedited by Ryanne DolanIteratorsedited by Ryanne DolanMonitorsedited by Ryanne DolanOperatorsedited by Ryanne DolanGeneratorsedited by Ryanne DolanView All Error Handling Go functions often return os.Error objects, which include a String() method. This allows the caller to check for an error condition as follows:if err http://www.golangpatterns.info/error-handling := api.Func(); err != nil { // handle err fmt.Println("err: " + err.String())}By convention, the err pointer will be nil unless there is an error condition.Bad Usage of ErrorsYou should avoid writing code like this:err1 := api.Func1()if err1 != nil { fmt.Println("err: " + err.String()) return}err2 := api.Func2()if err2 != nil {... return}...... or like this:var err os.Errorif error handling good == false { err = os.NewError("things aren't good")}if bad == true { err = os.NewError("things are bad")}if err != nil { fmt.Println("something's wrong: " + err.String())}In the first case, the errors are reported (by printing them) with if-statements scattered throughout the code. With this pattern, it is hard to tell what is normal program logic and what go error handling is error checking/reporting. Also notice that most of the code is dedicated to error conditions at any point in the code.In the second case, it's hard to tell where errors are coming from and to control when to stop and report an error. It's possible to use chained and nested if-else blocks to stop function execution when an error occurs, but this is what the return statement is for, after all!Only Return ErrorsAs a general rule, never assign an error to a variable except within a compound if-statement:if err := api.Func1(); err != nil {...} // very acceptableDon't report errors when you encounter them; rather, return an appropriate os.Error object and defer handling to the caller:func foo (good, bad bool) os.Error { if good == false { return os.NewError("things aren't good") } if bad == true { return os.NewError("things are bad") } return nil}If you must check for errors and report them in the same function, you can wrap your error conditions in a closure:func httpRequestHandler(w http.ResponseWriter, req *http.Request)