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What is the golang Errorf function?

Faraz Karim

Grokking Modern System Design Interview for Engineers & Managers

Ace your System Design Interview and take your career to the next level. Learn to handle the design of applications like Netflix, Quora, Facebook, Uber, and many more in a 45-min interview. Learn the RESHADED framework for architecting web-scale applications by determining requirements, constraints, and assumptions before diving into a step-by-step design process.

The Go programming language uses the Errorf function to generate a customized error message. It supports custom format specifiers and uses a format string to format the output string.

To use this function, you must import the fmt package in your file and access the Errorf function within, using the . notation: fmt.Errorf.

Here, Errorf is the actual function, while fmt is the Go package that stores the definition of this function.

Function definition

The definition of the Errorf function inside the fmt package is as follows:

Parameters

The fmt.Errorf function takes two parameters, described below:

  • format: This argument is of type string and represents the string containing custom specifiers that the Errorf uses to format the final output error.

  • a ...interface{}: This is the list of all arguments that replace specifier values in the format string to generate the final error message. There can be any number of input arguments and of any type.

Common specifiers

The following is a table of the most commonly used format specifiers in Go and their descriptions.

Specifiers Description
%s To print a string
%d To print an integer
%v To print values of all elements in a structure
%+v To print the names and values of all elements in a structure

Return values

The fmt.Errorf function returns the final error message, generated using the format string and the list of arguments. This output is of type error.

Examples

The following example is a simple program. We first initialize a variable with a string and use it with a format string to generate an error message that we then print out using the println function.

package main
import (
"fmt"
)
func main() {
quantity := 500
unit := "meters"
err := fmt.Errorf("The workshop is less that %d %s",quantity, unit)
fmt.Println(err)
}

Since the error message that is generated by the Errorf function is of type error, you can also use the Error method to access it. This is shown in the following example:

package main
import (
"fmt"
)
func main() {
organization := "Educative"
my_err := fmt.Errorf("Hello and welcome to %s", organization)
fmt.Println(my_err.Error())
}

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golang

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Faraz Karim
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Grokking Modern System Design Interview for Engineers & Managers

Ace your System Design Interview and take your career to the next level. Learn to handle the design of applications like Netflix, Quora, Facebook, Uber, and many more in a 45-min interview. Learn the RESHADED framework for architecting web-scale applications by determining requirements, constraints, and assumptions before diving into a step-by-step design process.

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