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fmt: x format verb for []byte fails in a recursive call to Fscanf from a scanln call in go1.5rc1 #12090

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ghost opened this issue Aug 10, 2015 · 2 comments
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fmt: x format verb for []byte fails in a recursive call to Fscanf from a scanln call in go1.5rc1 #12090

ghost opened this issue Aug 10, 2015 · 2 comments
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Go1.5

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@ghost
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ghost commented Aug 10, 2015

Consider the following code:

package main

import "fmt"

type arr [2]byte

func (x *arr) Scan(ss fmt.ScanState, verb rune) error {
    var b []byte
    _, err := fmt.Fscanf(ss, "%4x", &b)
    copy((*x)[:], b)
    return err
}

func main() {
    var x arr
    n, err := fmt.Sscanln("0123\n", &x)
    fmt.Println(n, err, x)
}

In go1.4.2 this prints 1 <nil> [1 35], but go1.5rc1 linux/amd64 gives me 1 expected newline [1 35], which doesn't seem right. Changing the format verb to 's' makes the error go away.
@ghost ghost changed the title fmt: Scanner fmt: x format verb for strings fails in a recursive call to Fscanf from a scanln call Aug 10, 2015
@ghost ghost changed the title fmt: x format verb for strings fails in a recursive call to Fscanf from a scanln call fmt: x format verb for strings fails in a recursive call to Fscanf from a scanln call in go1.5rc1 Aug 10, 2015
@davecheney
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@hubslave can you please provide a code sample that demonstrates the issue.

@ghost ghost changed the title fmt: x format verb for strings fails in a recursive call to Fscanf from a scanln call in go1.5rc1 fmt: x format verb for []byte fails in a recursive call to Fscanf from a scanln call in go1.5rc1 Aug 10, 2015
@robpike
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robpike commented Aug 10, 2015

Nice bug, easy fix coming.

@adg adg mentioned this issue Aug 10, 2015
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@mikioh mikioh added this to the Go1.5 milestone Aug 10, 2015
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