Stdlib.Marshal(3o) OCaml library Stdlib.Marshal(3o)
NAME
Stdlib.Marshal - no description
Module
Module Stdlib.Marshal
Documentation
Module Marshal
: (module Stdlib__Marshal)
type extern_flags =
| No_sharing (* Don't preserve sharing
*)
| Closures (* Send function closures
*)
| Compat_32 (* Ensure 32-bit compatibility
*)
The flags to the Marshal.to_* functions below.
val to_channel : out_channel -> 'a -> extern_flags list -> unit
Marshal.to_channel chan v flags writes the representation of v on chan-
nel chan . The flags argument is a possibly empty list of flags that
governs the marshaling behavior with respect to sharing, functional
values, and compatibility between 32- and 64-bit platforms.
If flags does not contain Marshal.No_sharing , circularities and shar-
ing inside the value v are detected and preserved in the sequence of
bytes produced. In particular, this guarantees that marshaling always
terminates. Sharing between values marshaled by successive calls to
Marshal.to_channel is neither detected nor preserved, though. If flags
contains Marshal.No_sharing , sharing is ignored. This results in
faster marshaling if v contains no shared substructures, but may cause
slower marshaling and larger byte representations if v actually con-
tains sharing, or even non-termination if v contains cycles.
If flags does not contain Marshal.Closures , marshaling fails when it
encounters a functional value inside v : only 'pure' data structures,
containing neither functions nor objects, can safely be transmitted be-
tween different programs. If flags contains Marshal.Closures , func-
tional values will be marshaled as a the position in the code of the
program together with the values corresponding to the free variables
captured in the closure. In this case, the output of marshaling can
only be read back in processes that run exactly the same program, with
exactly the same compiled code. (This is checked at un-marshaling time,
using an MD5 digest of the code transmitted along with the code posi-
tion.)
The exact definition of which free variables are captured in a closure
is not specified and can vary between bytecode and native code (and ac-
cording to optimization flags). In particular, a function value ac-
cessing a global reference may or may not include the reference in its
closure. If it does, unmarshaling the corresponding closure will cre-
ate a new reference, different from the global one.
If flags contains Marshal.Compat_32 , marshaling fails when it encoun-
ters an integer value outside the range [-2{^30}, 2{^30}-1] of integers
that are representable on a 32-bit platform. This ensures that mar-
shaled data generated on a 64-bit platform can be safely read back on a
32-bit platform. If flags does not contain Marshal.Compat_32 , integer
values outside the range [-2{^30}, 2{^30}-1] are marshaled, and can be
read back on a 64-bit platform, but will cause an error at un-marshal-
ing time when read back on a 32-bit platform. The Mashal.Compat_32
flag only matters when marshaling is performed on a 64-bit platform; it
has no effect if marshaling is performed on a 32-bit platform.
Raises Failure if chan is not in binary mode.
val to_bytes : 'a -> extern_flags list -> bytes
Marshal.to_bytes v flags returns a byte sequence containing the repre-
sentation of v . The flags argument has the same meaning as for Mar-
shal.to_channel .
Since 4.02.0
val to_string : 'a -> extern_flags list -> string
Same as to_bytes but return the result as a string instead of a byte
sequence.
val to_buffer : bytes -> int -> int -> 'a -> extern_flags list -> int
Marshal.to_buffer buff ofs len v flags marshals the value v , storing
its byte representation in the sequence buff , starting at index ofs ,
and writing at most len bytes. It returns the number of bytes actually
written to the sequence. If the byte representation of v does not fit
in len characters, the exception Failure is raised.
val from_channel : in_channel -> 'a
Marshal.from_channel chan reads from channel chan the byte representa-
tion of a structured value, as produced by one of the Marshal.to_*
functions, and reconstructs and returns the corresponding value.
Raises End_of_file if chan is already at the end of the file.
Raises Failure if the end of the file is reached during unmarshalling
itself or if chan is not in binary mode.
val from_bytes : bytes -> int -> 'a
Marshal.from_bytes buff ofs unmarshals a structured value like Mar-
shal.from_channel does, except that the byte representation is not read
from a channel, but taken from the byte sequence buff , starting at po-
sition ofs . The byte sequence is not mutated.
Since 4.02.0
val from_string : string -> int -> 'a
Same as from_bytes but take a string as argument instead of a byte se-
quence.
val header_size : int
The bytes representing a marshaled value are composed of a fixed-size
header and a variable-sized data part, whose size can be determined
from the header. Marshal.header_size is the size, in bytes, of the
header. Marshal.data_size buff ofs is the size, in bytes, of the data
part, assuming a valid header is stored in buff starting at position
ofs . Finally, Marshal.total_size buff ofs is the total size, in
bytes, of the marshaled value. Both Marshal.data_size and Marshal.to-
tal_size raise Failure if buff , ofs does not contain a valid header.
To read the byte representation of a marshaled value into a byte se-
quence, the program needs to read first Marshal.header_size bytes into
the sequence, then determine the length of the remainder of the repre-
sentation using Marshal.data_size , make sure the sequence is large
enough to hold the remaining data, then read it, and finally call Mar-
shal.from_bytes to unmarshal the value.
val data_size : bytes -> int -> int
See Marshal.header_size .
val total_size : bytes -> int -> int
See Marshal.header_size .
OCamldoc 2023-02-12 Stdlib.Marshal(3o)
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