[Solved] Golang error “invalid memory address or nil pointer dereference”, Why this happens? [duplicate]

Question

This occurs, as the error message says, when you try to dereference (use) nil. Without knowing which line the error was reported on, I would have to guess it’s here:

    cd, _ := r.Cookie("hello")

    if cd.Value == "username" {  // <-- This line
           // do ...
    }

Because you’re discarding the error from r.Cookie() instead of checking the error, so you don’t know that the cookie hello doesn’t exist, meaning cd is nil. So when you try to use cd.Value, you’re dereferencing a nil pointer, causing the panic you’re seeing.

Accepted Answer

This occurs, as the error message says, when you try to dereference (use) nil. Without knowing which line the error was reported on, I would have to guess it’s here:

    cd, _ := r.Cookie("hello")

    if cd.Value == "username" {  // <-- This line
           // do ...
    }

Because you’re discarding the error from r.Cookie() instead of checking the error, so you don’t know that the cookie hello doesn’t exist, meaning cd is nil. So when you try to use cd.Value, you’re dereferencing a nil pointer, causing the panic you’re seeing.