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...
HTH
- Hendrik
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