Why Does Go\'s fmt.Scanln Give an \'Expected Newline\' Error?

fmt.Scanln Error: Expected Newline

When utilizing the fmt.Scanln function in Go, you may encounter an "expected newline" error. This occurs when input contains a newline character before the expected delimiter (usually a space). To address this, let's delve into the behavior of fmt.Scan and fmt.Scanln.

fmt.Scan reads space-separated values from standard input, treating newlines as spaces. It assigns these values to the corresponding arguments, returning the count of successfully scanned items.

fmt.Scanln behaves similarly but stops scanning at a newline. Critically, the input must end with a newline or an EOF to complete successfully.

To illustrate this, consider the following input:

123
123.456
everybody loves ice cream

When using fmt.Scan, the output will be:

read 1 integer:  123
read 1 float64:  123.456
read 1 string:  everybody
Error:  Scan: expected newline

fmt.Scan interprets "everybody loves ice cream" as two strings, resulting in the error.

However, if you use fmt.Scanln for the same input, the output will be:

read 1 integer:  123
read 1 float64:  123.456
read 1 string:  everybody loves ice cream

fmt.Scanln recognizes the newline as the delimiter and correctly parses the entire line as a single string argument.

To read a line that ends with a newline character in Go, you can use bufio.Reader and its ReadString method:

line, err := buffer.ReadString('\n')

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