How to get the stacktrace of a panic (and store as a variable)

Question

As we all know, panics produce a stacktrace to stdout (Playground link).:

panic: runtime error: index out of range goroutine 1 [running]: main.main()     /tmp/sandbox579134920/main.go:9 +0x20 

And it seems when you recover from a panic, recover() returns only an error which describes what caused the panic (Playground link).

runtime error: index out of range 

My question is, is it possible to store the stacktrace which is written to stdout? This provides much better debugging information than the string runtime error: index out of range because it shows the exact line in a file which caused the panic.

Answer 1

Like @Volker mentioned above, and what was posted as a comment, we can use the runtime/debug package.

package main  import (     "fmt"     "runtime/debug" )  func main() {     defer func() {         if r := recover(); r != nil {             fmt.Println("stacktrace from panic: \n" + string(debug.Stack()))         }     }()      var mySlice []int     j := mySlice[0]      fmt.Printf("Hello, playground %d", j) } 

prints

stacktrace from panic:  goroutine 1 [running]: runtime/debug.Stack(0x1042ff18, 0x98b2, 0xf0ba0, 0x17d048)     /usr/local/go/src/runtime/debug/stack.go:24 +0xc0 main.main.func1()     /tmp/sandbox973508195/main.go:11 +0x60 panic(0xf0ba0, 0x17d048)     /usr/local/go/src/runtime/panic.go:502 +0x2c0 main.main()     /tmp/sandbox973508195/main.go:16 +0x60 

Playground link.