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<H1><A NAME="SECTION0011300000000000000000"></A><A NAME="memoryExamples"></A>
<BR>
9.3 Examples
</H1>

<P>
Here is the example from section <A href="memoryOverview.html#memoryOverview">9.1</A>, rewritten so
that the I/O buffer is allocated from the Python heap by using the
first function set:

<P>
<div class="verbatim"><pre>
    PyObject *res;
    char *buf = (char *) PyMem_Malloc(BUFSIZ); /* for I/O */

    if (buf == NULL)
        return PyErr_NoMemory();
    /* ...Do some I/O operation involving buf... */
    res = PyString_FromString(buf);
    PyMem_Free(buf); /* allocated with PyMem_Malloc */
    return res;
</pre></div>

<P>
The same code using the type-oriented function set:

<P>
<div class="verbatim"><pre>
    PyObject *res;
    char *buf = PyMem_New(char, BUFSIZ); /* for I/O */

    if (buf == NULL)
        return PyErr_NoMemory();
    /* ...Do some I/O operation involving buf... */
    res = PyString_FromString(buf);
    PyMem_Del(buf); /* allocated with PyMem_New */
    return res;
</pre></div>

<P>
Note that in the two examples above, the buffer is always
manipulated via functions belonging to the same set. Indeed, it
is required to use the same memory API family for a given
memory block, so that the risk of mixing different allocators is
reduced to a minimum. The following code sequence contains two errors,
one of which is labeled as <em>fatal</em> because it mixes two different
allocators operating on different heaps.

<P>
<div class="verbatim"><pre>
char *buf1 = PyMem_New(char, BUFSIZ);
char *buf2 = (char *) malloc(BUFSIZ);
char *buf3 = (char *) PyMem_Malloc(BUFSIZ);
...
PyMem_Del(buf3);  /* Wrong -- should be PyMem_Free() */
free(buf2);       /* Right -- allocated via malloc() */
free(buf1);       /* Fatal -- should be PyMem_Del()  */
</pre></div>

<P>
In addition to the functions aimed at handling raw memory blocks from
the Python heap, objects in Python are allocated and released with
<tt class="cfunction">PyObject_New()</tt>, <tt class="cfunction">PyObject_NewVar()</tt> and
<tt class="cfunction">PyObject_Del()</tt>, or with their corresponding macros
<tt class="cfunction">PyObject_NEW()</tt>, <tt class="cfunction">PyObject_NEW_VAR()</tt> and
<tt class="cfunction">PyObject_DEL()</tt>.

<P>
These will be explained in the next chapter on defining and
implementing new object types in C.

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<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
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