Proper way to free a pointer array in SWIG input typemap?

Question

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});

            


        

Answer 1

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);

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;
}