Lua 5.1, alien and C struct with string

[Markus Korber <korbse@...>]

Hi,

I'm trying to call a C library function in Lua5.1 via alien 0.7.0. The C 
struct takes a pointer to a string buffer. However, I do not know how to 
handle/allocate this buffer. When trying the solution below I get a 
segmentation fault. If I try to change the type of "d" to "pointer" then 
I can assign the buffer to "c.d". However, the shared lib does not print 
anything. Any ideas? Thanks in advance!

Wrap of shared lib (see below) in Lua:

require "alien"
def=alien.load("libmkoshared.so")
test = def.test

test:types{ ret = "int", "pointer" }

testit = alien.defstruct {
  { "a",     "int"     },
  { "d",     "string" }}

-- Create struct instance
c = testit:new()
c.a = 3

-- Try to alloc buffer for "d"
buf = alien.buffer("12345")
c.d = buf
-- print(alien.tostring(c.d))

-- Application call
r = test(c())
print(r)


Shared library:
Compile with: gcc -c -Wall -Werror -fPIC mkoshared.c && gcc -shared -o 
libmkoshared.so mkoshared.o

#include <stdio.h>
#include <string.h>

#define STRING_LENGTH 256
typedef char TString[STRING_LENGTH];

typedef struct TUSB
{
   int a;
   TString d;
} TUSB;

typedef TUSB * PUSB;

extern int test(PUSB p)
{
   printf("-%s-\n", (char*)p);
   return 2*(p->a);
}