Module Stdlib.Marshal
Contents
Instructions: Use this module in your project
In the IDE (CLion, Visual Studio Code, Xcode, etc.) you use for your DkSDK project:
Add the following to your project's
dependencies/CMakeLists.txt:DkSDKProject_DeclareAvailable(ocaml CONSTRAINT "= 4.14.0" FINDLIBS str unix runtime_events threads dynlink) DkSDKProject_MakeAvailable(ocaml)Add the
Findlib::ocamllibrary to any desired targets insrc/*/CMakeLists.txt:target_link_libraries(YourPackage_YourLibraryName # ... existing libraries, if any ... Findlib::ocaml)Click your IDE's
Buildbutton
Not using DkSDK?
FIRST, do one or all of the following:
Run:
opam install ocaml.4.14.0Edit your
dune-projectand add:(package (name YourExistingPackage) (depends ; ... existing dependenices ... (ocaml (>= 4.14.0))))Then run:
dune build *.opam # if this fails, run: dune buildEdit your
<package>.opamfile and add:depends: [ # ... existing dependencies ... "ocaml" {>= "4.14.0"} ]Then run:
opam install . --deps-only
FINALLY, add the library to any desired (library)and/or (executable) targets in your **/dune files:
(library
(name YourLibrary)
; ... existing library options ...
(libraries
; ... existing libraries ...
))
(executable
(name YourExecutable)
; ... existing executable options ...
(libraries
; ... existing libraries ...
))typeextern_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.
valto_channel :out_channel->'a->extern_flagslist``->unit
Marshal.to_channel chan v flags writes the representation of v on
channel 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
sharing 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
contains 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
between different programs. If flags contains Marshal.Closures,
functional 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
position.)
The exact definition of which free variables are captured in a closure is not specified and can vary between bytecode and native code (and according to optimization flags). In particular, a function value accessing a global reference may or may not include the reference in its closure. If it does, unmarshaling the corresponding closure will create a new reference, different from the global one.
If flags contains Marshal.Compat_32, marshaling fails when it
encounters an integer value outside the range [-2{^30}, 2{^30}-1] of
integers that are representable on a 32-bit platform. This ensures that
marshaled 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-marshaling 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
chanis not in binary mode.
valto_bytes :'a->extern_flagslist``->bytes
Marshal.to_bytes v flags returns a byte sequence containing the
representation of v. The flags argument has the same meaning as for
Marshal.to_channel.
- since 4.02.0
valto_string :'a->extern_flagslist``->string
Same as to_bytes but return the result as a string instead of a byte
sequence.
valto_buffer : ``bytes->``int->``int->'a->extern_flagslist``->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.
valfrom_channel :in_channel->'a
Marshal.from_channel chan reads from channel chan the byte
representation 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
chanis already at the end of the file. -
raises Failure
if the end of the file is reached during unmarshalling itself or if
chanis not in binary mode.
valfrom_bytes : ``bytes->``int->'a
Marshal.from_bytes buff ofs unmarshals a structured value like
Marshal.from_channel does, except that the byte
representation is not read from a channel, but taken from the byte
sequence buff, starting at position ofs. The byte sequence is not
mutated.
- since 4.02.0
valfrom_string : ``string->``int->'a
Same as from_bytes but take a string as argument instead of a byte
sequence.
valheader_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.total_size raise Failure if buff, ofs
does not contain a valid header.
To read the byte representation of a marshaled value into a byte
sequence, the program needs to read first
Marshal.header_size bytes into the sequence, then
determine the length of the remainder of the representation using
Marshal.data_size, make sure the sequence is large
enough to hold the remaining data, then read it, and finally call
Marshal.from_bytes to unmarshal the value.
valdata_size : ``bytes->``int->int
See Marshal.header_size.
valtotal_size : ``bytes->``int->int
See Marshal.header_size.
