在SWIG输入typemap中释放指针数组的正确方法? [英] Proper way to free a pointer array in SWIG input typemap?

问题描述

我正在尝试使用SWIG包装以下函数.

Hi I'm trying to wrap the following function using SWIG.

static void readTable(int argc, t_atom *argv) { //accepts table in Lua e.g. readTable({"ab",3});

        for (int i=0; i<argc; ++i) {

            if (argv[i].a_type == A_FLOAT)
                printf("FLOAT : %g\n", argv[i].a_w.w_float);
            else if (argv[i].a_type == A_SYMBOL)
                printf("SYMBOL : %s\n", argv[i].a_w.w_symbol->s_name);
        }
    }

这是我创建的类型图.

%include "exception.i"
%typemap(in) (int argc, t_atom *argv)
{
    if (!lua_istable(L, 1)) {
      SWIG_exception(SWIG_RuntimeError, "argument mismatch: table expected");
    }
    lua_len(L, 1);
    $1 = lua_tointeger(L, -1);
    $2 = (t_atom *)getbytes($1 * sizeof(t_atom)); //internally calls calloc()

    for (int i=0; i<$1; ++i) {

        lua_pushinteger(L, i+1);
        lua_gettable(L, 1);

        if(lua_isnumber(L, -1)) {

            $2[i].a_type = A_FLOAT;
            $2[i].a_w.w_float = lua_tonumber(L, -1);
        }          
        else if(lua_isstring(L, -1)) {

            $2[i].a_type = A_SYMBOL;
            $2[i].a_w.w_symbol = gensym(lua_tostring(L, -1));
        }
    }
    freebytes($2, $1 * sizeof(t_atom)); //internally calls free()
}

如您所见，我使用内部调用calloc()的getbytes()为数组分配内存，并使用内部调用free()的freebytes()释放内存.

As you can see, I allocate memory for an array using getbytes() which internally calls calloc() and free the memory using freebytes() which internally calls free().

令人惊讶的是，当我在Lua中调用readTable()函数时，它可以正常工作而不会崩溃.

Surprisingly, when I call readTable() function in Lua, it works fine without crashing.

例如，在Lua中调用test.readTable({3, "abc"})会显示以下结果.

for example, calling test.readTable({3, "abc"}) in Lua prints the following result.

FLOAT : 3
SYMBOL : abc

我的问题是

a)当我在SWIG界面中释放内存时，readTable()如何在不崩溃的情况下打印结果?也许没有正确释放内存?

a) How can readTable() print results without crashing when I freed the memory in SWIG interface? Maybe memory is not being properly freed?

b)如果a)没有意义或使用不安全，您是否建议改为在函数readTable()中调用freebytes()，使其类似于以下内容?

b) If a) doesn't make sense or is not safe to use, would you recommend calling the freebytes() inside the function readTable() instead so it can be like the following?

static void readTable(int argc, t_atom *argv) {

        for (int i=0; i<argc; ++i) {

            if (argv[i].a_type == A_FLOAT)
                post("FLOAT : %g", argv[i].a_w.w_float);
            else if (argv[i].a_type == A_SYMBOL)
                post("SYMBOL : %s", argv[i].a_w.w_symbol->s_name);
        }
        freebytes(argv, argc * sizeof(t_atom));
    }

推荐答案

这正是

That is exactly the situation which %typemap(freearg) is for.

%include "exception.i"

%typemap(in) (int argc, t_atom *argv) {
    if (!lua_istable(L, $input)) {
        SWIG_exception(SWIG_RuntimeError, "argument mismatch: table expected");
    }
    lua_len(L, $input);
    $1 = lua_tointeger(L, -1);
    $2 = (t_atom *)getbytes($1 * sizeof(t_atom)); // internally calls calloc()

    for (int i = 0; i < $1; ++i) {

        lua_pushinteger(L, i + 1);
        lua_gettable(L, $input);

        if (lua_isnumber(L, -1)) {
            $2[i].a_type = A_FLOAT;
            $2[i].a_w.w_float = lua_tonumber(L, -1);
        } else if (lua_isstring(L, -1)) {
            $2[i].a_type = A_SYMBOL;
            $2[i].a_w.w_symbol = gensym(lua_tostring(L, -1));
        } else {
            SWIG_exception(SWIG_RuntimeError, "unhandled argument type");
        }
    }
}

%typemap(freearg) (int argc, t_atom *argv) {
    freebytes($2, $1 * sizeof(t_atom)); // internally calls free()
}

static void readTable(const std::string &name, int argc, t_atom *argv);

这是从SWIG 3.0生成的代码

This is the generated code from SWIG 3.0

static int _wrap_readTable(lua_State* L) {
  int SWIG_arg = 0;
  std::string *arg1 = 0 ;
  int arg2 ;
  t_atom *arg3 = (t_atom *) 0 ;

  SWIG_check_num_args("readTable",2,2)
  if(!lua_isuserdata(L,1)) SWIG_fail_arg("readTable",1,"std::string const &");

  if (!SWIG_IsOK(SWIG_ConvertPtr(L,1,(void**)&arg1,SWIGTYPE_p_std__string,0))){
    SWIG_fail_ptr("readTable",1,SWIGTYPE_p_std__string);
  }

  {
    if (!lua_istable(L, 2)) {
      SWIG_exception(SWIG_RuntimeError, "argument mismatch: table expected");
    }
    lua_len(L, 2);
    arg2 = lua_tointeger(L, -1);
    arg3 = (t_atom *)getbytes(arg2 * sizeof(t_atom)); // internally calls calloc()

    for (int i = 0; i < arg2; ++i) {
      lua_pushinteger(L, i + 1);
      lua_gettable(L, 2);

      if (lua_isnumber(L, -1)) {
        arg3[i].a_type = A_FLOAT;
        arg3[i].a_w.w_float = lua_tonumber(L, -1);
      } else if (lua_isstring(L, -1)) {
        arg3[i].a_type = A_SYMBOL;
        arg3[i].a_w.w_symbol = gensym(lua_tostring(L, -1));
      } else {
        SWIG_exception(SWIG_RuntimeError, "unhandled argument type");
      }
    }
  }
  readTable((std::string const &)*arg1,arg2,arg3);

  {
    freebytes(arg3, arg2 * sizeof(t_atom)); // internally calls free()
  }
  return SWIG_arg;

  if(0) SWIG_fail;

fail:
  {
    freebytes(arg3, arg2 * sizeof(t_atom)); // internally calls free()
  }
  lua_error(L);
  return SWIG_arg;
}

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