Read file at byte location
I need to read a file at a specific location, given by a byte offset.
filePath := "test_file.txt"
byteOffset := 6
// Read file
How can I achieve this, if possible without reading the whole file in memory ?
go
asked Nov 24 '18 at 14:48
Graham SlickGraham Slick
2,84642855
add a comment |
I need to read a file at a specific location, given by a byte offset.
filePath := "test_file.txt"
byteOffset := 6
// Read file
How can I achieve this, if possible without reading the whole file in memory ?
go
asked Nov 24 '18 at 14:48
Graham SlickGraham Slick
2,84642855
2
File.Seek
– ThunderCat
Nov 24 '18 at 14:52
What have you tried? What problems do you have? You just need to open the file and useFile.Seek().
– icza
Nov 24 '18 at 14:52
add a comment |
I need to read a file at a specific location, given by a byte offset.
filePath := "test_file.txt"
byteOffset := 6
// Read file
How can I achieve this, if possible without reading the whole file in memory ?
go
asked Nov 24 '18 at 14:48
Graham SlickGraham Slick
2,84642855
I need to read a file at a specific location, given by a byte offset.
filePath := "test_file.txt"
byteOffset := 6
// Read file
How can I achieve this, if possible without reading the whole file in memory ?
go
go
asked Nov 24 '18 at 14:48
Graham SlickGraham Slick
2,84642855
asked Nov 24 '18 at 14:48
Graham SlickGraham Slick
2,84642855
asked Nov 24 '18 at 14:48
Graham SlickGraham Slick
2,84642855
asked Nov 24 '18 at 14:48
Graham SlickGraham Slick
2,84642855
asked Nov 24 '18 at 14:48
Graham SlickGraham Slick
2,84642855
2,84642855
2
File.Seek
– ThunderCat
Nov 24 '18 at 14:52
What have you tried? What problems do you have? You just need to open the file and useFile.Seek().
– icza
Nov 24 '18 at 14:52
add a comment |
2
File.Seek
– ThunderCat
Nov 24 '18 at 14:52
What have you tried? What problems do you have? You just need to open the file and useFile.Seek().
– icza
Nov 24 '18 at 14:52
2
2
File.Seek
– ThunderCat
Nov 24 '18 at 14:52
File.Seek
– ThunderCat
Nov 24 '18 at 14:52
What have you tried? What problems do you have? You just need to open the file and use
File.Seek().– icza
Nov 24 '18 at 14:52
What have you tried? What problems do you have? You just need to open the file and use
File.Seek().– icza
Nov 24 '18 at 14:52
add a comment |
1 Answer
1
active
oldest
votes
Package os
import "os"
func (*File) Seek
func (f *File) Seek(offset int64, whence int) (ret int64, err error)
Seek sets the offset for the next Read or Write on file to offset,
interpreted according to whence: 0 means relative to the origin of the
file, 1 means relative to the current offset, and 2 means relative to
the end. It returns the new offset and an error, if any. The behavior
of Seek on a file opened with O_APPEND is not specified.
Package io
import "io"
Seek whence values.
const (
SeekStart = 0 // seek relative to the origin of the file
SeekCurrent = 1 // seek relative to the current offset
SeekEnd = 2 // seek relative to the end
)
For example,
package main
import (
"fmt"
"io"
"os"
)
func main() {
filePath := "test.file"
byteOffset := 6
f, err := os.Open(filePath)
if err != nil {
panic(err)
}
defer f.Close()
_, err = f.Seek(int64(byteOffset), io.SeekStart)
if err != nil {
panic(err)
}
buf := make(byte, 16)
n, err := f.Read(buf[:cap(buf)])
buf = buf[:n]
if err != nil {
if err != io.EOF {
panic(err)
}
}
fmt.Printf("%sn", buf)
}
Output:
$ cat test.file
0123456789
$ go run seek.go
6789
$
answered Nov 24 '18 at 14:54
peterSOpeterSO
96.3k15160178
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
Package os
import "os"
func (*File) Seek
func (f *File) Seek(offset int64, whence int) (ret int64, err error)
Seek sets the offset for the next Read or Write on file to offset,
interpreted according to whence: 0 means relative to the origin of the
file, 1 means relative to the current offset, and 2 means relative to
the end. It returns the new offset and an error, if any. The behavior
of Seek on a file opened with O_APPEND is not specified.
Package io
import "io"
Seek whence values.
const (
SeekStart = 0 // seek relative to the origin of the file
SeekCurrent = 1 // seek relative to the current offset
SeekEnd = 2 // seek relative to the end
)
For example,
package main
import (
"fmt"
"io"
"os"
)
func main() {
filePath := "test.file"
byteOffset := 6
f, err := os.Open(filePath)
if err != nil {
panic(err)
}
defer f.Close()
_, err = f.Seek(int64(byteOffset), io.SeekStart)
if err != nil {
panic(err)
}
buf := make(byte, 16)
n, err := f.Read(buf[:cap(buf)])
buf = buf[:n]
if err != nil {
if err != io.EOF {
panic(err)
}
}
fmt.Printf("%sn", buf)
}
Output:
$ cat test.file
0123456789
$ go run seek.go
6789
$
answered Nov 24 '18 at 14:54
peterSOpeterSO
96.3k15160178
add a comment |
Package os
import "os"
func (*File) Seek
func (f *File) Seek(offset int64, whence int) (ret int64, err error)
Seek sets the offset for the next Read or Write on file to offset,
interpreted according to whence: 0 means relative to the origin of the
file, 1 means relative to the current offset, and 2 means relative to
the end. It returns the new offset and an error, if any. The behavior
of Seek on a file opened with O_APPEND is not specified.
Package io
import "io"
Seek whence values.
const (
SeekStart = 0 // seek relative to the origin of the file
SeekCurrent = 1 // seek relative to the current offset
SeekEnd = 2 // seek relative to the end
)
For example,
package main
import (
"fmt"
"io"
"os"
)
func main() {
filePath := "test.file"
byteOffset := 6
f, err := os.Open(filePath)
if err != nil {
panic(err)
}
defer f.Close()
_, err = f.Seek(int64(byteOffset), io.SeekStart)
if err != nil {
panic(err)
}
buf := make(byte, 16)
n, err := f.Read(buf[:cap(buf)])
buf = buf[:n]
if err != nil {
if err != io.EOF {
panic(err)
}
}
fmt.Printf("%sn", buf)
}
Output:
$ cat test.file
0123456789
$ go run seek.go
6789
$
answered Nov 24 '18 at 14:54
peterSOpeterSO
96.3k15160178
add a comment |
Package os
import "os"
func (*File) Seek
func (f *File) Seek(offset int64, whence int) (ret int64, err error)
Seek sets the offset for the next Read or Write on file to offset,
interpreted according to whence: 0 means relative to the origin of the
file, 1 means relative to the current offset, and 2 means relative to
the end. It returns the new offset and an error, if any. The behavior
of Seek on a file opened with O_APPEND is not specified.
Package io
import "io"
Seek whence values.
const (
SeekStart = 0 // seek relative to the origin of the file
SeekCurrent = 1 // seek relative to the current offset
SeekEnd = 2 // seek relative to the end
)
For example,
package main
import (
"fmt"
"io"
"os"
)
func main() {
filePath := "test.file"
byteOffset := 6
f, err := os.Open(filePath)
if err != nil {
panic(err)
}
defer f.Close()
_, err = f.Seek(int64(byteOffset), io.SeekStart)
if err != nil {
panic(err)
}
buf := make(byte, 16)
n, err := f.Read(buf[:cap(buf)])
buf = buf[:n]
if err != nil {
if err != io.EOF {
panic(err)
}
}
fmt.Printf("%sn", buf)
}
Output:
$ cat test.file
0123456789
$ go run seek.go
6789
$
answered Nov 24 '18 at 14:54
peterSOpeterSO
96.3k15160178
Package os
import "os"
func (*File) Seek
func (f *File) Seek(offset int64, whence int) (ret int64, err error)
Seek sets the offset for the next Read or Write on file to offset,
interpreted according to whence: 0 means relative to the origin of the
file, 1 means relative to the current offset, and 2 means relative to
the end. It returns the new offset and an error, if any. The behavior
of Seek on a file opened with O_APPEND is not specified.
Package io
import "io"
Seek whence values.
const (
SeekStart = 0 // seek relative to the origin of the file
SeekCurrent = 1 // seek relative to the current offset
SeekEnd = 2 // seek relative to the end
)
For example,
package main
import (
"fmt"
"io"
"os"
)
func main() {
filePath := "test.file"
byteOffset := 6
f, err := os.Open(filePath)
if err != nil {
panic(err)
}
defer f.Close()
_, err = f.Seek(int64(byteOffset), io.SeekStart)
if err != nil {
panic(err)
}
buf := make(byte, 16)
n, err := f.Read(buf[:cap(buf)])
buf = buf[:n]
if err != nil {
if err != io.EOF {
panic(err)
}
}
fmt.Printf("%sn", buf)
}
Output:
$ cat test.file
0123456789
$ go run seek.go
6789
$
answered Nov 24 '18 at 14:54
peterSOpeterSO
96.3k15160178
edited Nov 24 '18 at 15:15
answered Nov 24 '18 at 14:54
peterSOpeterSO
96.3k15160178
answered Nov 24 '18 at 14:54
peterSOpeterSO
96.3k15160178
answered Nov 24 '18 at 14:54
peterSOpeterSO
96.3k15160178
96.3k15160178
add a comment |
add a comment |
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2
File.Seek
– ThunderCat
Nov 24 '18 at 14:52
What have you tried? What problems do you have? You just need to open the file and use
File.Seek().– icza
Nov 24 '18 at 14:52