# Process math.h
#
# (note: this requires py2.6, since that is when c_longdouble first appeared)
#
# Looking in math_c.py, we see some useful definitions, but not all
# that much, yet...

h2xml /usr/include/math.h -o math_c.xml
xml2py math_c.xml -o math_c.py



# Add the -c argument : include C preprocessor headers
#
# Now, we see a lot more defined in the math_c.py .  For example,
# M_PI, as defined in math.h, is included.

h2xml /usr/include/math.h -c -o math_c.xml
xml2py math_c.xml -o math_c.py



# -l: auto-load a library
#
# When you pass the -l argument, it will scan the libary for
# executable symbols.  If it finds them, it will automatically set up
# to run, using ctypes, from that library.  In this example, math_c.py
# becomes a module which automatically interface to libm

h2xml /usr/include/math.h -c -o math_c.xml
xml2py math_c.xml -o math_c.py -l /lib/libm.so.6

# In math_c.py:
# 
# | _libraries['/lib/libm.so.6'] = CDLL('/lib/libm.so.6')
# | 
# | log10 = _libraries['/lib/libm.so.6'].log10
# | log10.restype = c_double
# | log10.argtypes = [c_double]
#
# which is an automatic ctypes interface to log10 in libm
# To use it:

python2.6
>>> import math_c
>>> math_c.log10(100)
2.0



########################################

# Let's play with time.h (works on python2.5):
#
# We get a lot of stuff, for example, the ctypes definition of the C
# structure "struct tm" is automatically created, for example:
#
# | class tm(Structure):
# |     pass
# | tm._fields_ = [
# |     ('tm_sec', c_int),
# |     ('tm_min', c_int),
# |     ('tm_hour', c_int),
# |     ('tm_mday', c_int),
# |     ('tm_mon', c_int),
# |     ('tm_year', c_int),
# |     ('tm_wday', c_int),
# |     ('tm_yday', c_int),
# |     ('tm_isdst', c_int),
# |     ('tm_gmtoff', c_long),
# |     ('tm_zone', STRING),
# | ]
#
# We also have various functions defined:
# 
# | _libraries['/lib/libc.so.6'] = CDLL('/lib/libc.so.6')
# | 
# | strptime = _libraries['/lib/libc.so.6'].strptime
# | strptime.restype = STRING
# | strptime.argtypes = [STRING, STRING, POINTER(tm)]


# We use '-l /lib/libc.so.6', so that we automaticall set up to run
# defined functions from libc.so.6, using ctypes

h2xml /usr/include/time.h -o time_c.xml
xml2py time_c.xml -o time_c.py -l /lib/libc.so.6

man strptime
python
>>> import time_c
# Initialize a `struct tm` object to use as the return values of our
# function call.
>>> tm = time_c.tm()
# Call strptime, with two strings and a pointer to the struct_tm.  Read
# the manual page on strptime to understand the return value.
>>> time_c.strptime("Dec 19, 1985", "%b %d, %Y", tm)
''
# And our data structure is filled in:
>>> tm.tm_yday
352
>>> tm.tm_year
85
>>> tm.tm_wday
4

# In short, anything in a C header file, we can now do from Python
# using ctypes, without having to define a ctypes interface manually.