1 .. highlightlang:: c 2 3 .. _marshalling-utils: 4 5 Data marshalling support 6 ======================== 7 8 These routines allow C code to work with serialized objects using the same 9 data format as the :mod:`marshal` module. There are functions to write data 10 into the serialization format, and additional functions that can be used to 11 read the data back. Files used to store marshalled data must be opened in 12 binary mode. 13 14 Numeric values are stored with the least significant byte first. 15 16 The module supports two versions of the data format: version ``0`` is the 17 historical version, version ``1`` (new in Python 2.4) shares interned strings in 18 the file, and upon unmarshalling. Version 2 (new in Python 2.5) uses a binary 19 format for floating point numbers. *Py_MARSHAL_VERSION* indicates the current 20 file format (currently 2). 21 22 23 .. c:function:: void PyMarshal_WriteLongToFile(long value, FILE *file, int version) 24 25 Marshal a :c:type:`long` integer, *value*, to *file*. This will only write 26 the least-significant 32 bits of *value*; regardless of the size of the 27 native :c:type:`long` type. 28 29 .. versionchanged:: 2.4 30 *version* indicates the file format. 31 32 33 .. c:function:: void PyMarshal_WriteObjectToFile(PyObject *value, FILE *file, int version) 34 35 Marshal a Python object, *value*, to *file*. 36 37 .. versionchanged:: 2.4 38 *version* indicates the file format. 39 40 41 .. c:function:: PyObject* PyMarshal_WriteObjectToString(PyObject *value, int version) 42 43 Return a string object containing the marshalled representation of *value*. 44 45 .. versionchanged:: 2.4 46 *version* indicates the file format. 47 48 49 The following functions allow marshalled values to be read back in. 50 51 XXX What about error detection? It appears that reading past the end of the 52 file will always result in a negative numeric value (where that's relevant), 53 but it's not clear that negative values won't be handled properly when there's 54 no error. What's the right way to tell? Should only non-negative values be 55 written using these routines? 56 57 58 .. c:function:: long PyMarshal_ReadLongFromFile(FILE *file) 59 60 Return a C :c:type:`long` from the data stream in a :c:type:`FILE\*` opened 61 for reading. Only a 32-bit value can be read in using this function, 62 regardless of the native size of :c:type:`long`. 63 64 65 .. c:function:: int PyMarshal_ReadShortFromFile(FILE *file) 66 67 Return a C :c:type:`short` from the data stream in a :c:type:`FILE\*` opened 68 for reading. Only a 16-bit value can be read in using this function, 69 regardless of the native size of :c:type:`short`. 70 71 72 .. c:function:: PyObject* PyMarshal_ReadObjectFromFile(FILE *file) 73 74 Return a Python object from the data stream in a :c:type:`FILE\*` opened for 75 reading. On error, sets the appropriate exception (:exc:`EOFError` or 76 :exc:`TypeError`) and returns *NULL*. 77 78 79 .. c:function:: PyObject* PyMarshal_ReadLastObjectFromFile(FILE *file) 80 81 Return a Python object from the data stream in a :c:type:`FILE\*` opened for 82 reading. Unlike :c:func:`PyMarshal_ReadObjectFromFile`, this function 83 assumes that no further objects will be read from the file, allowing it to 84 aggressively load file data into memory so that the de-serialization can 85 operate from data in memory rather than reading a byte at a time from the 86 file. Only use these variant if you are certain that you won't be reading 87 anything else from the file. On error, sets the appropriate exception 88 (:exc:`EOFError` or :exc:`TypeError`) and returns *NULL*. 89 90 91 .. c:function:: PyObject* PyMarshal_ReadObjectFromString(char *string, Py_ssize_t len) 92 93 Return a Python object from the data stream in a character buffer 94 containing *len* bytes pointed to by *string*. On error, sets the 95 appropriate exception (:exc:`EOFError` or :exc:`TypeError`) and returns 96 *NULL*. 97 98 .. versionchanged:: 2.5 99 This function used an :c:type:`int` type for *len*. This might require 100 changes in your code for properly supporting 64-bit systems. 101
