[ python-Bugs-1072182 ] bad arg type to isspace in struct module

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Bugs item #1072182, was opened at 2004-11-23 23:35
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Category: Python Library
Group: Python 2.3
Status: Open
Resolution: None
Priority: 5
Submitted By: Greg McFarlane (gregm)
Assigned to: Nobody/Anonymous (nobody)
Summary: bad arg type to isspace in struct module

Initial Comment:
For characters greater than 0x7f, the calls to
isspace() in Modules/structmodule.c can return random
values.  For example, on Solaris I got this (incorrect)
output:

>>> import struct
>>> struct.calcsize('10d\xfed')
88
>>> 

After changing the three occurrences of
"isspace((int)c)" to "isspace((unsigned char)c)", this
was the (correct) output:

>>> import struct
>>> struct.calcsize('10d\xfed')
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
struct.error: bad char in struct format
>>> 

Reason: the '\xfe' is taken as a signed char.  The code
(int)c converts this to a signed int (-2).  The system
isspace macro uses this as an index into the __ctype
array.  The array is only defined for the values 0 to
255 and so -2 is out-of-bounds.  The value returned by
isspace depends on what happens to be at that location
in memory.

NOTE: There may be other occurrences of this bug in
other parts of the python code.  Please check.


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