The documents are too simple to explain clearly on anything. Besides the eating/chomping behavior, does an item include the space/newline following it? Either answer will not satisfy the behavior of the following code, by either answer, there should one case reports an error.
https://go.dev/play/p/XQFwxxiz2NA package main import "fmt" import "strings" func main() { { var r = strings.NewReader("xxx yyy\n") var x, y string n, err := fmt.Fscanln(r, &x, &y) fmt.Println(n, err, x, y, len(y)) // 2 <nil> xxx yyy 3 } { var r = strings.NewReader("xxx yyy \n") var x, y string n, err := fmt.Fscanln(r, &x, &y) fmt.Println(n, err, x, y, len(y)) // 2 <nil> xxx yyy 3 } } On Friday, January 31, 2025 at 4:11:48 AM UTC+8 Brian Candler wrote: > I guess not, but since it uses a plain io.Reader which doesn't support > peek or pushback, I can't think of any other behavior which is possible. > > On Thursday, 30 January 2025 at 19:27:51 UTC tapi...@gmail.com wrote: > >> On Tuesday, January 28, 2025 at 7:07:15 PM UTC+8 Brian Candler wrote: >> >> > The documentation tells that Fscanln() is similar to Fscan(), my test >> shows that it isn't true for some cases. >> >> "similar" does not mean "the same as". >> >> Fscanln chomps the fields given, then chomps the next character. If the >> next character is newline, it's happy. If the next character is not a >> newline, then it's unhappy and returns an error. At this point, you know >> the input was bad. >> >> No guarantees are made about the state of the input after an error, and >> as you've found, the next character (which *should* have been a newline) >> has been chomped. >> >> >> It looks the eating/chomping behavior is not well documented. >> >> >> >> On Tuesday, 28 January 2025 at 10:07:28 UTC Ivan Burak wrote: >> >> Hi Howard >> >> Thank you for the answer. >> >> My data is easier, it contains only 2 lines: >> Go version go1.22.11 windows/amd64 >> Build simple, secure, scalable systems with Go >> >> I did some tests and to speedup coding decided to use Fscanln(). >> I don't use this function in real programming, it's too slow. >> There are many ways to parse texts in Golang that fast and stable. >> >> My test algorithm didn't work, and when I realized what the reason was, I >> was just surprised. >> The documentation tells that Fscanln() is similar to Fscan(), my test >> shows that it isn't true for some cases. >> In my opinion the documentation or the function should be corrected. >> That's it. :) >> >> >> fmt.Fscanln(in2,&one,&two,&three,&four) >> That works but you know in our profession, usually we don't know the >> exact amount of data being processed >> (number of tokens, records, data volumes etc.), so we have to code based >> on estimates n, n^2, n^3 ... and we don't know the real n. >> >> thanks >> ivan >> >> On Monday, January 27, 2025 at 11:29:32 PM UTC+3 Howard C. Shaw III wrote: >> >> In your example, you are repeatedly reading one 'item' from the line. >> This is the source of the confusion, as this is not how Fscanln works - >> when you do this, *each* item is the documented 'final item' after which >> there must be a newline. >> >> That is, your data would look more like this: >> space separated column headers >> first second third last >> some data with the >> same pattern of columns >> >> and your read would be pulling all of those items from one line: >> fmt.Fscanln(in2,&one,&two,&three,&four) >> >> It is expected/designed to read one line of data at a time, and for you >> to know in advance the number of items in the line, and to expect to >> receive an error if they don't match. It is also expected that each column >> will have a consistent datatype, and for that to match the types of your >> parameters, and to error if the data can't be parsed. >> >> For parsing arbitrary string data, you might be better off just using >> bufio.Scanner with bufio.ScanWords. >> >> -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion visit https://groups.google.com/d/msgid/golang-nuts/02535533-5308-4bf4-bb9a-7016b95bfcf6n%40googlegroups.com.
