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55 | <H1><A NAME="SECTION007400000000000000000"></A><A NAME="marshalling-utils"></A> | |
56 | <BR> | |
57 | 5.4 Data marshalling support | |
58 | </H1> | |
59 | ||
60 | <P> | |
61 | These routines allow C code to work with serialized objects using the | |
62 | same data format as the <tt class="module">marshal</tt> module. There are functions | |
63 | to write data into the serialization format, and additional functions | |
64 | that can be used to read the data back. Files used to store marshalled | |
65 | data must be opened in binary mode. | |
66 | ||
67 | <P> | |
68 | Numeric values are stored with the least significant byte first. | |
69 | ||
70 | <P> | |
71 | The module supports two versions of the data format: version 0 is the | |
72 | historical version, version 1 (new in Python 2.4) shares interned | |
73 | strings in the file, and upon unmarshalling. <var>Py_MARSHAL_VERSION</var> | |
74 | indicates the current file format (currently 1). | |
75 | ||
76 | <P> | |
77 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"><td><nobr>void <b><tt id='l2h-200' xml:id='l2h-200' class="cfunction">PyMarshal_WriteLongToFile</tt></b>(</nobr></td><td>long <var>value</var>, FILE *<var>file</var>, int <var>version</var>)</td></tr></table></dt> | |
78 | <dd> | |
79 | Marshal a <tt class="ctype">long</tt> integer, <var>value</var>, to <var>file</var>. This | |
80 | will only write the least-significant 32 bits of <var>value</var>; | |
81 | regardless of the size of the native <tt class="ctype">long</tt> type. | |
82 | ||
83 | <P> | |
84 | ||
85 | <span class="versionnote">Changed in version 2.4: | |
86 | <var>version</var> indicates the file format.</span> | |
87 | ||
88 | </dd></dl> | |
89 | ||
90 | <P> | |
91 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"><td><nobr>void <b><tt id='l2h-201' xml:id='l2h-201' class="cfunction">PyMarshal_WriteObjectToFile</tt></b>(</nobr></td><td>PyObject *<var>value</var>, | |
92 | FILE *<var>file</var>, int <var>version</var>)</td></tr></table></dt> | |
93 | <dd> | |
94 | Marshal a Python object, <var>value</var>, to <var>file</var>. | |
95 | ||
96 | <P> | |
97 | ||
98 | <span class="versionnote">Changed in version 2.4: | |
99 | <var>version</var> indicates the file format.</span> | |
100 | ||
101 | </dd></dl> | |
102 | ||
103 | <P> | |
104 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"><td><nobr>PyObject* <b><tt id='l2h-202' xml:id='l2h-202' class="cfunction">PyMarshal_WriteObjectToString</tt></b>(</nobr></td><td>PyObject *<var>value</var>, int <var>version</var>)</td></tr></table></dt> | |
105 | <dd> | |
106 | <div class="refcount-info"> | |
107 | <span class="label">Return value:</span> | |
108 | <span class="value">New reference.</span> | |
109 | </div> | |
110 | Return a string object containing the marshalled representation of | |
111 | <var>value</var>. | |
112 | ||
113 | <P> | |
114 | ||
115 | <span class="versionnote">Changed in version 2.4: | |
116 | <var>version</var> indicates the file format.</span> | |
117 | ||
118 | </dd></dl> | |
119 | ||
120 | <P> | |
121 | The following functions allow marshalled values to be read back in. | |
122 | ||
123 | <P> | |
124 | XXX What about error detection? It appears that reading past the end | |
125 | of the file will always result in a negative numeric value (where | |
126 | that's relevant), but it's not clear that negative values won't be | |
127 | handled properly when there's no error. What's the right way to tell? | |
128 | Should only non-negative values be written using these routines? | |
129 | ||
130 | <P> | |
131 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"><td><nobr>long <b><tt id='l2h-203' xml:id='l2h-203' class="cfunction">PyMarshal_ReadLongFromFile</tt></b>(</nobr></td><td>FILE *<var>file</var>)</td></tr></table></dt> | |
132 | <dd> | |
133 | Return a C <tt class="ctype">long</tt> from the data stream in a <tt class="ctype">FILE*</tt> | |
134 | opened for reading. Only a 32-bit value can be read in using | |
135 | this function, regardless of the native size of <tt class="ctype">long</tt>. | |
136 | </dd></dl> | |
137 | ||
138 | <P> | |
139 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"><td><nobr>int <b><tt id='l2h-204' xml:id='l2h-204' class="cfunction">PyMarshal_ReadShortFromFile</tt></b>(</nobr></td><td>FILE *<var>file</var>)</td></tr></table></dt> | |
140 | <dd> | |
141 | Return a C <tt class="ctype">short</tt> from the data stream in a <tt class="ctype">FILE*</tt> | |
142 | opened for reading. Only a 16-bit value can be read in using | |
143 | this function, regardless of the native size of <tt class="ctype">short</tt>. | |
144 | </dd></dl> | |
145 | ||
146 | <P> | |
147 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"><td><nobr>PyObject* <b><tt id='l2h-205' xml:id='l2h-205' class="cfunction">PyMarshal_ReadObjectFromFile</tt></b>(</nobr></td><td>FILE *<var>file</var>)</td></tr></table></dt> | |
148 | <dd> | |
149 | <div class="refcount-info"> | |
150 | <span class="label">Return value:</span> | |
151 | <span class="value">New reference.</span> | |
152 | </div> | |
153 | Return a Python object from the data stream in a <tt class="ctype">FILE*</tt> | |
154 | opened for reading. On error, sets the appropriate exception | |
155 | (<tt class="exception">EOFError</tt> or <tt class="exception">TypeError</tt>) and returns <tt class="constant">NULL</tt>. | |
156 | </dd></dl> | |
157 | ||
158 | <P> | |
159 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"><td><nobr>PyObject* <b><tt id='l2h-206' xml:id='l2h-206' class="cfunction">PyMarshal_ReadLastObjectFromFile</tt></b>(</nobr></td><td>FILE *<var>file</var>)</td></tr></table></dt> | |
160 | <dd> | |
161 | <div class="refcount-info"> | |
162 | <span class="label">Return value:</span> | |
163 | <span class="value">New reference.</span> | |
164 | </div> | |
165 | Return a Python object from the data stream in a <tt class="ctype">FILE*</tt> | |
166 | opened for reading. Unlike | |
167 | <tt class="cfunction">PyMarshal_ReadObjectFromFile()</tt>, this function assumes | |
168 | that no further objects will be read from the file, allowing it to | |
169 | aggressively load file data into memory so that the de-serialization | |
170 | can operate from data in memory rather than reading a byte at a time | |
171 | from the file. Only use these variant if you are certain that you | |
172 | won't be reading anything else from the file. On error, sets the | |
173 | appropriate exception (<tt class="exception">EOFError</tt> or | |
174 | <tt class="exception">TypeError</tt>) and returns <tt class="constant">NULL</tt>. | |
175 | </dd></dl> | |
176 | ||
177 | <P> | |
178 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"><td><nobr>PyObject* <b><tt id='l2h-207' xml:id='l2h-207' class="cfunction">PyMarshal_ReadObjectFromString</tt></b>(</nobr></td><td>char *<var>string</var>, | |
179 | int <var>len</var>)</td></tr></table></dt> | |
180 | <dd> | |
181 | <div class="refcount-info"> | |
182 | <span class="label">Return value:</span> | |
183 | <span class="value">New reference.</span> | |
184 | </div> | |
185 | Return a Python object from the data stream in a character buffer | |
186 | containing <var>len</var> bytes pointed to by <var>string</var>. On error, | |
187 | sets the appropriate exception (<tt class="exception">EOFError</tt> or | |
188 | <tt class="exception">TypeError</tt>) and returns <tt class="constant">NULL</tt>. | |
189 | </dd></dl> | |
190 | ||
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