101 lines
3.9 KiB
ReStructuredText
101 lines
3.9 KiB
ReStructuredText
.. highlightlang:: c
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.. _marshalling-utils:
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Data marshalling support
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========================
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These routines allow C code to work with serialized objects using the same
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data format as the :mod:`marshal` module. There are functions to write data
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into the serialization format, and additional functions that can be used to
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read the data back. Files used to store marshalled data must be opened in
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binary mode.
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Numeric values are stored with the least significant byte first.
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The module supports two versions of the data format: version ``0`` is the
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historical version, version ``1`` (new in Python 2.4) shares interned strings in
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the file, and upon unmarshalling. Version 2 (new in Python 2.5) uses a binary
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format for floating point numbers. *Py_MARSHAL_VERSION* indicates the current
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file format (currently 2).
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.. c:function:: void PyMarshal_WriteLongToFile(long value, FILE *file, int version)
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Marshal a :c:type:`long` integer, *value*, to *file*. This will only write
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the least-significant 32 bits of *value*; regardless of the size of the
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native :c:type:`long` type.
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.. versionchanged:: 2.4
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*version* indicates the file format.
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.. c:function:: void PyMarshal_WriteObjectToFile(PyObject *value, FILE *file, int version)
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Marshal a Python object, *value*, to *file*.
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.. versionchanged:: 2.4
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*version* indicates the file format.
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.. c:function:: PyObject* PyMarshal_WriteObjectToString(PyObject *value, int version)
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Return a string object containing the marshalled representation of *value*.
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.. versionchanged:: 2.4
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*version* indicates the file format.
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The following functions allow marshalled values to be read back in.
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XXX What about error detection? It appears that reading past the end of the
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file will always result in a negative numeric value (where that's relevant),
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but it's not clear that negative values won't be handled properly when there's
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no error. What's the right way to tell? Should only non-negative values be
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written using these routines?
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.. c:function:: long PyMarshal_ReadLongFromFile(FILE *file)
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Return a C :c:type:`long` from the data stream in a :c:type:`FILE\*` opened
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for reading. Only a 32-bit value can be read in using this function,
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regardless of the native size of :c:type:`long`.
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.. c:function:: int PyMarshal_ReadShortFromFile(FILE *file)
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Return a C :c:type:`short` from the data stream in a :c:type:`FILE\*` opened
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for reading. Only a 16-bit value can be read in using this function,
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regardless of the native size of :c:type:`short`.
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.. c:function:: PyObject* PyMarshal_ReadObjectFromFile(FILE *file)
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Return a Python object from the data stream in a :c:type:`FILE\*` opened for
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reading. On error, sets the appropriate exception (:exc:`EOFError` or
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:exc:`TypeError`) and returns *NULL*.
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.. c:function:: PyObject* PyMarshal_ReadLastObjectFromFile(FILE *file)
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Return a Python object from the data stream in a :c:type:`FILE\*` opened for
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reading. Unlike :c:func:`PyMarshal_ReadObjectFromFile`, this function
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assumes that no further objects will be read from the file, allowing it to
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aggressively load file data into memory so that the de-serialization can
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operate from data in memory rather than reading a byte at a time from the
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file. Only use these variant if you are certain that you won't be reading
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anything else from the file. On error, sets the appropriate exception
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(:exc:`EOFError` or :exc:`TypeError`) and returns *NULL*.
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.. c:function:: PyObject* PyMarshal_ReadObjectFromString(char *string, Py_ssize_t len)
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Return a Python object from the data stream in a character buffer
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containing *len* bytes pointed to by *string*. On error, sets the
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appropriate exception (:exc:`EOFError` or :exc:`TypeError`) and returns
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*NULL*.
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.. versionchanged:: 2.5
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This function used an :c:type:`int` type for *len*. This might require
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changes in your code for properly supporting 64-bit systems.
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