如何在 OS X 中包含 FFI？

我在构建时遇到问题这个项目 https://github.com/metaeducation/ren-c启用 FFI 扩展。为了隔离问题，我正在尝试编译这个例子 http://www.chiark.greenend.org.uk/doc/libffi-dev/html/Closure-Example.html（全文包含在下面）。

我正在使用 OS X 10.13.2、Xcode 9.2 并安装了命令行工具（确认/usr/include/ffi/ffi.h存在）。我修改了示例，因此包含行读取include <ffi/ffi.h>.

在没有选项的情况下调用编译器，我得到以下结果：

$ gcc closure.test.c
closure.test.c:23:13: warning: implicit declaration of function 'ffi_closure_alloc' is invalid in C99 [-Wimplicit-function-declaration]
  closure = ffi_closure_alloc(sizeof(ffi_closure), &bound_puts);
            ^
closure.test.c:23:11: warning: incompatible integer to pointer conversion assigning to 'ffi_closure *' (aka 'struct ffi_closure *') from
      'int' [-Wint-conversion]
  closure = ffi_closure_alloc(sizeof(ffi_closure), &bound_puts);
          ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
closure.test.c:35:15: warning: implicit declaration of function 'ffi_prep_closure_loc' is invalid in C99 [-Wimplicit-function-declaration]
          if (ffi_prep_closure_loc(closure, &cif, puts_binding,
              ^
closure.test.c:45:3: warning: implicit declaration of function 'ffi_closure_free' is invalid in C99 [-Wimplicit-function-declaration]
  ffi_closure_free(closure);
  ^
4 warnings generated.
Undefined symbols for architecture x86_64:
  "_ffi_closure_alloc", referenced from:
      _main in closure-7b0e9b.o
  "_ffi_closure_free", referenced from:
      _main in closure-7b0e9b.o
  "_ffi_prep_cif", referenced from:
      _main in closure-7b0e9b.o
  "_ffi_prep_closure_loc", referenced from:
      _main in closure-7b0e9b.o
  "_ffi_type_pointer", referenced from:
      _main in closure-7b0e9b.o
  "_ffi_type_sint32", referenced from:
      _main in closure-7b0e9b.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

我需要什么选项/修改来纠正这个问题？

来源closure.test.c:

#include <stdio.h>
#include <ffi.h>

/* Acts like puts with the file given at time of enclosure. */
void puts_binding(ffi_cif *cif, void *ret, void* args[],
                  void *stream)
{
  *(ffi_arg *)ret = fputs(*(char **)args[0], (FILE *)stream);
}

typedef int (*puts_t)(char *);

int main()
{
  ffi_cif cif;
  ffi_type *args[1];
  ffi_closure *closure;

  void *bound_puts;
  int rc;

  /* Allocate closure and bound_puts */
  closure = ffi_closure_alloc(sizeof(ffi_closure), &bound_puts);

  if (closure)
    {
      /* Initialize the argument info vectors */
      args[0] = &ffi_type_pointer;

      /* Initialize the cif */
      if (ffi_prep_cif(&cif, FFI_DEFAULT_ABI, 1,
                       &ffi_type_sint, args) == FFI_OK)
        {
          /* Initialize the closure, setting stream to stdout */
          if (ffi_prep_closure_loc(closure, &cif, puts_binding,
                                   stdout, bound_puts) == FFI_OK)
            {
              rc = ((puts_t)bound_puts)("Hello World!");
              /* rc now holds the result of the call to fputs */
            }
        }
    }

  /* Deallocate both closure, and bound_puts */
  ffi_closure_free(closure);

  return 0;
}

好吧，看来你可以这样做来修复它：

$ cd
$ git clone https://github.com/libffi/libffi
$ cd libffi/
$ ./autogen.sh
$ ./configure
$ make
$ make install

这将构建libffi从源头开始，即使你有，它也会起作用libffi安装自brew，因为这个新版本将安装在/usr/local并且不在Cellar.

那么你不需要改变#include，保持这样#include <ffi.h>，打开一个终端到您隔离的 c 源所在的文件夹并发出问题gcc -o ffi -lffi ffi.c（假设它是您拥有的源文件）。

teixeira: ~/etudes_c $ ./ffi
Hello World!