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Invalid memory address or nil pointer dereference
source link: https://yourbasic.org/golang/gotcha-nil-pointer-dereference/
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Invalid memory address or nil pointer dereference
yourbasic.org/golang
Why does this program panic?
type Point struct {
X, Y float64
}
func (p *Point) Abs() float64 {
return math.Sqrt(p.X*p.X + p.Y*p.Y)
}
func main() {
var p *Point
fmt.Println(p.Abs())
}panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0xffffffff addr=0x0 pc=0xd2c5a]
goroutine 1 [running]:
main.(*Point).Abs(...)
../main.go:6
main.main()
../main.go:11 +0x1aAnswer
The uninitialized pointer p in the main function is nil,
and you can’t follow the nil pointer.
If
xis nil, an attempt to evaluate*xwill cause a run-time panic. The Go Programming Language Specification: Address operators
You need to create a Point:
func main() {
var p *Point = new(Point)
fmt.Println(p.Abs())
}Since methods with pointer receivers take either a value or a pointer, you could also skip the pointer altogether:
func main() {
var p Point // has zero value Point{X:0, Y:0}
fmt.Println(p.Abs())
}See Pointers for more about pointers in Go.
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