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 shares interned strings in the file, and upon 18 unmarshalling. Version 2 uses a binary format for floating point numbers. 19 *Py_MARSHAL_VERSION* indicates the current file format (currently 2). 20 21 22 .. c:function:: void PyMarshal_WriteLongToFile(long value, FILE *file, int version) 23 24 Marshal a :c:type:`long` integer, *value*, to *file*. This will only write 25 the least-significant 32 bits of *value*; regardless of the size of the 26 native :c:type:`long` type. *version* indicates the file format. 27 28 29 .. c:function:: void PyMarshal_WriteObjectToFile(PyObject *value, FILE *file, int version) 30 31 Marshal a Python object, *value*, to *file*. 32 *version* indicates the file format. 33 34 35 .. c:function:: PyObject* PyMarshal_WriteObjectToString(PyObject *value, int version) 36 37 Return a string object containing the marshalled representation of *value*. 38 *version* indicates the file format. 39 40 41 The following functions allow marshalled values to be read back in. 42 43 XXX What about error detection? It appears that reading past the end of the 44 file will always result in a negative numeric value (where that's relevant), 45 but it's not clear that negative values won't be handled properly when there's 46 no error. What's the right way to tell? Should only non-negative values be 47 written using these routines? 48 49 50 .. c:function:: long PyMarshal_ReadLongFromFile(FILE *file) 51 52 Return a C :c:type:`long` from the data stream in a :c:type:`FILE\*` opened 53 for reading. Only a 32-bit value can be read in using this function, 54 regardless of the native size of :c:type:`long`. 55 56 On error, raise an exception and return ``-1``. 57 58 59 .. c:function:: int PyMarshal_ReadShortFromFile(FILE *file) 60 61 Return a C :c:type:`short` from the data stream in a :c:type:`FILE\*` opened 62 for reading. Only a 16-bit value can be read in using this function, 63 regardless of the native size of :c:type:`short`. 64 65 On error, raise an exception and return ``-1``. 66 67 68 .. c:function:: PyObject* PyMarshal_ReadObjectFromFile(FILE *file) 69 70 Return a Python object from the data stream in a :c:type:`FILE\*` opened for 71 reading. 72 73 On error, sets the appropriate exception (:exc:`EOFError` or 74 :exc:`TypeError`) and returns *NULL*. 75 76 77 .. c:function:: PyObject* PyMarshal_ReadLastObjectFromFile(FILE *file) 78 79 Return a Python object from the data stream in a :c:type:`FILE\*` opened for 80 reading. Unlike :c:func:`PyMarshal_ReadObjectFromFile`, this function 81 assumes that no further objects will be read from the file, allowing it to 82 aggressively load file data into memory so that the de-serialization can 83 operate from data in memory rather than reading a byte at a time from the 84 file. Only use these variant if you are certain that you won't be reading 85 anything else from the file. 86 87 On error, sets the appropriate exception (:exc:`EOFError` or 88 :exc:`TypeError`) and returns *NULL*. 89 90 91 .. c:function:: PyObject* PyMarshal_ReadObjectFromString(const 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*. 95 96 On error, sets the appropriate exception (:exc:`EOFError` or 97 :exc:`TypeError`) and returns *NULL*. 98 99
