Scan vs. Scanln in Go: Understanding the Expected Newline Behavior

fmt.Scanln Expected Newline Error: Understanding the Behavior

The fmt.Scanln function in Go raises an error when encountering a missing newline after reading a line of input. This behavior, unlike the getline method in C , is intentional and driven by the specific implementation of fmt.Scanln.

Scan vs. Scanln

fmt.Scan reads input space-separated values and stores them in the specified arguments. Newlines are treated as space characters. In contrast, fmt.Scanln stops scanning at a newline, and there must be a newline after the last item scanned. This difference arises from their intended usage:

• fmt.Scan is used to scan multiple individual space-separated values on a single line.
• fmt.Scanln is designed to scan a complete line of input, including any whitespace characters and the newline.

The Error

When using fmt.Scanln without a newline after the input, an error is triggered because the function expects a newline to terminate the line. The error message, "Scan: expected newline," indicates this condition.

Comparison with getline in C

The getline method in C reads a line of input and stores it in a provided string variable. Unlike fmt.Scanln, getline does not require a newline at the end of the input. This difference is due to the fact that getline is typically used for reading entire lines, whereas fmt.Scanln is designed for scanning specific values within a line.

Alternative for Line Reading

If you need to read a complete line of input in Go, you can use the ReadString method of the bufio.Reader type:

<code class="go">line, err := buffer.ReadString('\n')</code>

This method reads input until a newline character is encountered and stores the line in the line variable.

By understanding the behavior of fmt.Scanln and its difference from C 's getline method, you can effectively use these functions to handle input parsing in your Go programs.

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