projects / OpenSPARC-T2-DV / blame
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| 53 | ||
| 54 | <H1><A NAME="SECTION0011300000000000000000"></A><A NAME="memoryExamples"></A> | |
| 55 | <BR> | |
| 56 | 9.3 Examples | |
| 57 | </H1> | |
| 58 | ||
| 59 | <P> | |
| 60 | Here is the example from section <A href="memoryOverview.html#memoryOverview">9.1</A>, rewritten so | |
| 61 | that the I/O buffer is allocated from the Python heap by using the | |
| 62 | first function set: | |
| 63 | ||
| 64 | <P> | |
| 65 | <div class="verbatim"><pre> | |
| 66 | PyObject *res; | |
| 67 | char *buf = (char *) PyMem_Malloc(BUFSIZ); /* for I/O */ | |
| 68 | ||
| 69 | if (buf == NULL) | |
| 70 | return PyErr_NoMemory(); | |
| 71 | /* ...Do some I/O operation involving buf... */ | |
| 72 | res = PyString_FromString(buf); | |
| 73 | PyMem_Free(buf); /* allocated with PyMem_Malloc */ | |
| 74 | return res; | |
| 75 | </pre></div> | |
| 76 | ||
| 77 | <P> | |
| 78 | The same code using the type-oriented function set: | |
| 79 | ||
| 80 | <P> | |
| 81 | <div class="verbatim"><pre> | |
| 82 | PyObject *res; | |
| 83 | char *buf = PyMem_New(char, BUFSIZ); /* for I/O */ | |
| 84 | ||
| 85 | if (buf == NULL) | |
| 86 | return PyErr_NoMemory(); | |
| 87 | /* ...Do some I/O operation involving buf... */ | |
| 88 | res = PyString_FromString(buf); | |
| 89 | PyMem_Del(buf); /* allocated with PyMem_New */ | |
| 90 | return res; | |
| 91 | </pre></div> | |
| 92 | ||
| 93 | <P> | |
| 94 | Note that in the two examples above, the buffer is always | |
| 95 | manipulated via functions belonging to the same set. Indeed, it | |
| 96 | is required to use the same memory API family for a given | |
| 97 | memory block, so that the risk of mixing different allocators is | |
| 98 | reduced to a minimum. The following code sequence contains two errors, | |
| 99 | one of which is labeled as <em>fatal</em> because it mixes two different | |
| 100 | allocators operating on different heaps. | |
| 101 | ||
| 102 | <P> | |
| 103 | <div class="verbatim"><pre> | |
| 104 | char *buf1 = PyMem_New(char, BUFSIZ); | |
| 105 | char *buf2 = (char *) malloc(BUFSIZ); | |
| 106 | char *buf3 = (char *) PyMem_Malloc(BUFSIZ); | |
| 107 | ... | |
| 108 | PyMem_Del(buf3); /* Wrong -- should be PyMem_Free() */ | |
| 109 | free(buf2); /* Right -- allocated via malloc() */ | |
| 110 | free(buf1); /* Fatal -- should be PyMem_Del() */ | |
| 111 | </pre></div> | |
| 112 | ||
| 113 | <P> | |
| 114 | In addition to the functions aimed at handling raw memory blocks from | |
| 115 | the Python heap, objects in Python are allocated and released with | |
| 116 | <tt class="cfunction">PyObject_New()</tt>, <tt class="cfunction">PyObject_NewVar()</tt> and | |
| 117 | <tt class="cfunction">PyObject_Del()</tt>, or with their corresponding macros | |
| 118 | <tt class="cfunction">PyObject_NEW()</tt>, <tt class="cfunction">PyObject_NEW_VAR()</tt> and | |
| 119 | <tt class="cfunction">PyObject_DEL()</tt>. | |
| 120 | ||
| 121 | <P> | |
| 122 | These will be explained in the next chapter on defining and | |
| 123 | implementing new object types in C. | |
| 124 | ||
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| 159 | <span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span> | |
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