Golang中的Reader如何在循环中自动迭代？

Question

I'm reading about how to use CSVs in Golang and came across this code:

csvFile, _ := os.Open("people.csv")
reader := csv.NewReader(bufio.NewReader(csvFile))
var people []Person
for {
    line, error := reader.Read()
    if error == io.EOF {
        break
    } else if error != nil {
        log.Fatal(error)
    }
    people = append(people, Person{
        Firstname: line[0],
        Lastname:  line[1],
    })
}

Located here: https://www.thepolyglotdeveloper.com/2017/03/parse-csv-data-go-programming-language/

What I find confusing here is with the infinite for-loop, each iteration grabs the next line but there's no lineNum++ type logic being passed into the Reader. How does the reader know which iteration its on? How can I change this? E.g. grab just the first line.

Answer 1

How does a Reader in Golang automatically iterate in a loop? How does the reader know which iteration its on?

The Read method returns the next record by consuming more data from the underlying io.Reader. The Read method returns io.EOF when there are no more records in the underlying reader.

The application is responsible for calling read in a loop as shown in the example.

The Reader does not need to know the line number to read the next record, but the Reader does maintain a line counter in its internal state for annotating errors.

If the application needs to know the line number, the application can declare a counter and increment the counter on each read.

How can I change this? E.g. grab just the first line.

Call Read once:

f, err := os.Open("people.csv")
if err != nil {
    // handle error
} 
defer f.Close()

r := csv.NewReader(f)
firstLine, err := r.Read()
if err != nil {
   // handle error
}