how to write file appendly

[xf wang]

   ioutil.WriteFile(filename string, data []byte, perm uint32)

when using ioutil.WriteFile(fileName,[]byte(err),0644),

0644 means overwritting,

anyone know how to append file instead of overwitting?

[Russ Cox]

WriteFile always overwrites.
To append you have to open the file yourself.
Copy the source to WriteFile and open it with
os.O_APPEND instead of os.O_TRUNC.

godoc -src io/ioutil WriteFile

Russ

[xf wang]

f_price,_:=os.Open("history.txt",os.O_APPEND|os.O_RDWR,0666)

io.WriteString(f_price,str )

it is still overwritten instead of being appended?

[peterGo]

It works.

package main

import ("fmt";"io";"io/ioutil";"os")

const file = "temp.txt"

func write(flag int, text string) {
f, err:=os.Open(file, flag, 0666)
if err != nil { fmt.Println(err); return }
n, err := io.WriteString(f, text)
if err != nil { fmt.Println(n, err); return }
f.Close()
data, err := ioutil.ReadFile(file)
if err != nil { fmt.Println(err); return }
fmt.Println(string(data))
}

func main() {
write(os.O_CREAT|os.O_TRUNC|os.O_RDWR, "new")
for i := 0; i < 2; i++ {
write(os.O_APPEND|os.O_RDWR, "|append")
}
}

Output:
new
new|append
new|append|append

Peter

[xf wang]

 i copy your code and run it,

and

output in temp.txt:

|append

environment: windows xp,

golang version:2010-09-06

[Rob 'Commander' Pike]

That sounds like a bug in the Windows version.

-rob

[brainman]

Thank you for the test case <g>!

http://code.google.com/p/go/issues/detail?id=1124

[brainman]

On Sep 20, 10:13 am, xf wang <wxf6...@gmail.com> wrote:
>  i copy your code and run it,

Looks like a bug:

http://code.google.com/p/go/issues/detail?id=1124

Alex

[Skip Tavakkolian]

i think a problem is in src/pkg/syscall/syscall_windows.go in function
Open (sorry, i can't build Go on windows yet):

func Open(path string, mode int, perm uint32) (fd int, errno int) {
if len(path) == 0 {
return -1, ERROR_FILE_NOT_FOUND
}
var access uint32
switch mode & (O_RDONLY | O_WRONLY | O_RDWR) {
case O_RDONLY:
access = GENERIC_READ
case O_WRONLY:
access = GENERIC_WRITE
case O_RDWR:
access = GENERIC_READ | GENERIC_WRITE
}
// should probably add the following
if mode&O_APPEND {
access |= FILE_APPEND_DATA
// and probably should also do:
// access &= ^GENERIC_WRITE
}

-Skip

[brainman]

On Sep 20, 2:59 pm, Skip Tavakkolian <skip.tavakkol...@gmail.com>
wrote:

> i think a problem is in src/pkg/syscall/syscall_windows.go in function
> Open (sorry, i can't build Go on windows yet):
>

Yes, it looks like O_APPEND have not been implemented yet.

> // should probably add the following
>         if mode&O_APPEND {
>                 access |= FILE_APPEND_DATA
>                 // and probably should also do:
>                 // access &= ^GENERIC_WRITE
>         }

I'm not sure if it is possible. But, if nothing else, WriteFile with
special offset of 0xFFFFFFFF (see lpOverlapped) parameter should do
that trick.

Thanks for your suggestion.

Alex