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Python Library Reference |  |
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ctypes defines a number of primitive C compatible data types :
| ctypes type | C type | Python type |
|---|---|---|
| c_char |
char
|
1-character string |
| c_wchar |
wchar_t
|
1-character unicode string |
| c_byte |
char
|
int/long |
| c_ubyte |
unsigned char
|
int/long |
| c_short |
short
|
int/long |
| c_ushort |
unsigned short
|
int/long |
| c_int |
int
|
int/long |
| c_uint |
unsigned int
|
int/long |
| c_long |
long
|
int/long |
| c_ulong |
unsigned long
|
int/long |
| c_longlong |
__int64 or
long long
|
int/long |
| c_ulonglong |
unsigned __int64 or
unsigned long long
|
int/long |
| c_float |
float
|
float |
| c_double |
double
|
float |
| c_char_p |
char *
(NUL terminated)
|
string or
None
|
| c_wchar_p |
wchar_t *
(NUL terminated)
|
unicode or
None
|
| c_void_p |
void *
|
int/long
or None
|
All these types can be created by calling them with an optional initializer of the correct type and value:
>>> c_int()
c_long(0)
>>> c_char_p("Hello, World")
c_char_p('Hello, World')
>>> c_ushort(-3)
c_ushort(65533)
>>>
Since these types are mutable, their value can also be changed afterwards:
>>> i = c_int(42) >>> print i c_long(42) >>> print i.value 42 >>> i.value = -99 >>> print i.value -99 >>>
Assigning a new value to instances of the pointer types c_char_p, c_wchar_p, and c_void_p changes the memory location they point to, not the contents of the memory block (of course not, because Python strings are immutable):
>>> s = "Hello, World"
>>> c_s = c_char_p(s)
>>> print c_s
c_char_p('Hello, World')
>>> c_s.value = "Hi, there"
>>> print c_s
c_char_p('Hi, there')
>>> print s # first string is unchanged
Hello, World
>>>
You should be careful, however, not to pass them to functions
expecting pointers to mutable memory. If you need mutable memory
blocks, ctypes has a create_string_buffer function which creates
these in various ways. The current memory block contents can be
accessed (or changed) with the raw property, if you want to access
it as NUL terminated string, use the string property:
>>> from ctypes import *
>>> p = create_string_buffer(3) # create a 3 byte buffer, initialized to NUL bytes
>>> print sizeof(p), repr(p.raw)
3 '\x00\x00\x00'
>>> p = create_string_buffer("Hello") # create a buffer containing a NUL terminated string
>>> print sizeof(p), repr(p.raw)
6 'Hello\x00'
>>> print repr(p.value)
'Hello'
>>> p = create_string_buffer("Hello", 10) # create a 10 byte buffer
>>> print sizeof(p), repr(p.raw)
10 'Hello\x00\x00\x00\x00\x00'
>>> p.value = "Hi"
>>> print sizeof(p), repr(p.raw)
10 'Hi\x00lo\x00\x00\x00\x00\x00'
>>>
The create_string_buffer function replaces the c_buffer
function (which is still available as an alias), as well as the
c_string function from earlier ctypes releases. To create a
mutable memory block containing unicode characters of the C type
wchar_t use the create_unicode_buffer function.
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Python Library Reference | |
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