undefined: fmt

'fmt' is a standard library package in Go used for formatted I/O. If you see 'undefined: fmt', it means that the code is trying to use 'fmt' without importing it first.

This error occurs because the Go compiler cannot find the 'fmt' package in the current file. This typically happens when the import statement for 'fmt' is missing or incorrectly specified.

To fix this error, you need to add an import statement for the 'fmt' package at the beginning of your Go file. Ensure that the import statement is correctly formatted.