How to Customize Go\'s Print Output for Structs with Pointers?

Customizing the Print Output of Structs with Pointers

When printing structs with pointers in Go, using the default %v format specifier may not provide the desired result. This is because it prints the pointer address instead of the content of the referenced struct.

To address this, there are two primary approaches: define a custom String method for the struct type or manually format the output.

Defining a Custom String Method

The preferred method is to implement the Stringer interface for the involved struct types. This can be done by adding a String() string method to the struct. The format string passed to the printf function will call this method instead.

For example:

package main

import "fmt"

type A struct {
    a int32
    B *B
}

type B struct{ b int32 }

func (aa *A) String() string {
    return fmt.Sprintf("A{a:%d, B:%v}",aa.a,aa.B)
}

func (bb *B) String() string {
    return fmt.Sprintf("B{b:%d}",bb.b)
}

func main() {
    a := &A{a: 1, B: &B{b: 2}}
    fmt.Printf("v ==== %v \n", a) // Prints "v ==== A{a:1, B:B{b:2}}"
}

Manual Formatting

In the absence of a String method, you can format the output manually using the format specifiers of the individual struct members.

package main

import "fmt"

type A struct {
    a int32
    B *B
}

type B struct{ b int32 }

func main() {
    a := &A{a: 1, B: &B{b: 2}}
    fmt.Printf("v ==== A{a:%d, B:B{b:%d}}\n", a.a, a.B.b)
}

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