Ur C FFI Example

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Revision as of 10:31, 14 January 2010 by 161.159.4.33 (Talk)

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The Ur C FFI makes it easy to interface with C libraries. Here is a simple example project that uses the FFI. The complete source is available in a tarball.

For a detailed reference, see the manual.

Contents

The Library

The following files live in a subdirectory lib of the base directory for our example.

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lib.h

We need to restate this interface in a way that GCC can understand.

#include <urweb.h>

uw_Basis_string uw_Lib_hello(uw_context, uw_unit);
uw_Basis_string uw_Lib_important(uw_context, uw_Basis_string);
uw_Basis_int uw_Lib_counter(uw_context, uw_unit);

lib.c

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

#include <urweb.h>

uw_Basis_string uw_Lib_hello(uw_context ctx, uw_unit u) {
  return "Hello";
}

uw_Basis_string uw_Lib_important(uw_context ctx, uw_Basis_string s) {
  uw_Basis_string s2 = uw_malloc(ctx, strlen(s)+2);

  sprintf(s2, "%s!", s);
  return s2;
}

static int counter;

uw_Basis_int uw_Lib_counter(uw_context ctx, uw_unit u) {
  return counter++;
}

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Makefile

CFLAGS := -I/usr/local/include/urweb

all: lib.o

Client Application

Here is one way to use the library we just defined, based out of subdirectory app.

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main.urs

val main : unit -> transaction page

app.urp

library ../lib/lib

main
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