"Hendrik van Rooyen" <m...@microcorp.co.za> wrote in message
news:000f01c96822$5c300f00$0d00a...@hendrik...
Red Rackham wrote:
I would like to pass a string into a dll function. I notice that to pass
using
ctypes, it has to be a ctypes type. >Looking at the ctypes doc page I
don't see
a c_string class.
The following seems to work for me:
In the c programme:
/*
This routine outputs and inputs a symmetric block of bytes, writing
the outputs out and reading the inputs in, replacing the chars in the
original output string
*/
unsigned char read_write (unsigned char *inputs, unsigned char *outputs,
int
lenin, int lenout)
{
int i = 0;
int addr = 0;
int addrhi = 0;
int oind = 0;
char rv;
while (i < lenin)
{
addrhi = i >> 8 & 0x3f; // we can have 64 * 256 adresses in the
top
6 + 8 bits
addr = i & 0xff; // this is low order
rv = put_1(addrhi|0xd0); // put out the addy
rv = put_3(addr);
rv = put_1(addrhi|0x90); // make a read strobe on bit 6
inputs[i] = get_0() ^ 255; // read the char
rv = put_1(addr|0xd0); // raise strobe again
i++;
}
while (i < lenin + lenout)
{
oind = i - lenin; // index into outputs start at 0
addrhi = i >> 8 & 0x3f; // we can have 64 * 256 adresses in the
top
6 + 8 bits
addr = i & 0xff; // this is low order
rv = put_1(addrhi|0xd0); // put out the addy
rv = put_3(addr);
rv = put_0(outputs[oind]); // put out the output
rv = put_1(addrhi|0x50); // make a write strobe on bit 7
rv = put_1(addrhi|0xd0); // raise write strobe again
i++;
}
return *inputs;
}
Then in the python it is used as follows:
import sys, os, ctypes, time
io = ctypes.cdll.LoadLibrary('./lib_gpio.a')
def do_io(ins, outs): # ins and outs are normal python strings that must
exist
# this routine happens to work by side effect - the ins string is
changed by the c routine
r = io.read_write(ins,outs,len(ins),len(outs))
return
The c routine will actually break Python's normal string
immmutability and give you back a changed ins.
It is in general not a good idea to change the passed string
like I am doing - but you wanted to know how
to pass a python string, and the outs example should get
you going - a string is an array of characters in c...
Here's an example using mutable buffers:
------------ x.c --> x.dll -----------------------
#include <string.h>
__declspec(dllexport)
int fill(char *buf,int len)
{
strncpy(buf,"initialized string",len-1);
buf[len-1]=0;
return strlen(buf);
}
--------------------------------------------------
PythonWin 2.6.1 (r261:67517, Dec 4 2008, 16:51:00) [MSC v.1500 32 bit
(Intel)] on win32.
Portions Copyright 1994-2008 Mark Hammond - see 'Help/About PythonWin' for
further copyright information.
from ctypes import *
x=CDLL('x.dll')
s=create_string_buffer('string',10)
s.raw
'string\x00\x00\x00\x00'
s.value
'string'
x.fill(s,len(s))
9
s.raw
'initializ\x00'
s.value
'initializ'
s=create_string_buffer('string',20)
x.fill(s,len(s))
18
s.raw
'initialized string\x00\x00'
s.value
'initialized string'
--Mark
--
http://mail.python.org/mailman/listinfo/python-list
