create_string_buffer how to get used size

Question

How can I determine the used size/length of a buffer created with create_string_buffer?

buffer = create_string_buffer(1000)

e.g. in buffer I have 3 values and 997 unused -> how it's possible to get the 3?

Answer 1

Is there any reason you can't just do len(buffer.value)?

For pure theoretical fun of it -- I see no reason to do this if you can use the above method -- I'll mention that you can also do buffer.raw.find("\x00") or list(buffer).index("\x00"). These fail if the string is not properly null-terminated though.

Answer 2

In [1]: from ctypes import *

In [2]: s = create_string_buffer(1000)

In [3]: s[0] = '1'

In [4]: s[1] = '2'

In [5]: s[2] = '3'

In [6]: s
Out[6]: <ctypes.c_char_Array_1000 at 0x8ca126c>

In [7]: for i, c in enumerate(s):
   ...:     if c == '\x00':
   ...:         break
   ...:         

In [8]: i
Out[8]: 3

C-Strings are null-terminated, so loop over the string until you find '\x00'.

Answer 3

You could:

1. Have the function populating the buffer return the amount of buffer used.
2. Look for a terminating condition of the buffer such as nul.
3. Initialize the buffer with a value never used in the data, then look for that terminating the data.