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fmt: unexpected newline error #10853

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syst3mw0rm opened this issue May 14, 2015 · 4 comments
Closed

fmt: unexpected newline error #10853

syst3mw0rm opened this issue May 14, 2015 · 4 comments
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@syst3mw0rm
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@syst3mw0rm syst3mw0rm commented May 14, 2015

The following program crashes with panic:

package main

import (
    "fmt"
    "bytes"
)

func main() {
    var a, b int
    r := bytes.NewReader([]byte{'1', '\n', '2'})

    _, err := fmt.Fscanf(r, "%d", &a)
    if err != nil {
        panic(err)
    }

    _, err = fmt.Fscanf(r, "%d", &b)
    if err != nil {
        panic(err)
    }
}
panic: unexpected newline

goroutine 1 [running]:
main.main()
    /tmp/f.go:19 +0x33d
exit status 2

on commit b83b011

@c9s
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@c9s c9s commented May 29, 2015

I think this behavior is correct. if you run the program with go1.4.2, the result is the same: unexpected newline

/usr/local/go/bin/go version
go version go1.4.2 darwin/amd64

/usr/local/go/bin/go run test.go
panic: unexpected newline

goroutine 1 [running]:
main.main()
    /Users/c9s/go/test.go:19 +0x3e0

goroutine 2 [runnable]:
runtime.forcegchelper()
    /usr/local/go/src/runtime/proc.go:90
runtime.goexit()
    /usr/local/go/src/runtime/asm_amd64.s:2232 +0x1

goroutine 3 [runnable]:
runtime.bgsweep()
    /usr/local/go/src/runtime/mgc0.go:82
runtime.goexit()
    /usr/local/go/src/runtime/asm_amd64.s:2232 +0x1

goroutine 4 [runnable]:
runtime.runfinq()
    /usr/local/go/src/runtime/malloc.go:712
runtime.goexit()
    /usr/local/go/src/runtime/asm_amd64.s:2232 +0x1
exit status 2
@robpike
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@robpike robpike commented Jun 5, 2015

Working as intended. The first call to Fscanf reads the '1'. The second call expects another integer but instead encounters a newline. It's not well explained in the documentation (and that will be addressed, so I'm leaving this bug open for now), but if there is no newline in the pattern, scanning stops at a newline.

@robpike
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@robpike robpike commented Jun 5, 2015

Duplicate of #9459

@robpike robpike closed this Jun 5, 2015
@syst3mw0rm
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@syst3mw0rm syst3mw0rm commented Jun 9, 2015

It's not exactly duplicate of #9459

Explicitly mentioning about behaviour being different than corresponding C routines well explains it in documentation - CL10779.

@golang golang locked and limited conversation to collaborators Jun 25, 2016
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