Question

I hava a class like：

class SomeClass
{
   void initFromBuffer(void* buffer,int length);
   void initFromString(const std::string& str);
}

Using tolua++, got the binding like:

static int SomeClass_initFromBuffer00(lua_State* tolua_S)
{
  SomeClass* self = (SomeClass*)  tolua_tousertype(tolua_S,1,0);
  void* buffer = ((void*)  tolua_touserdata(tolua_S,2,0));
  int length = ((int)  tolua_tonumber(tolua_S,3,0));
  self->initFromBuffer(buffer,length);
}

and:

static int SomeClass_initFromString00(lua_State* tolua_S)
{

   SomeClass* self = (SomeClass*)  tolua_tousertype(tolua_S,1,0);
   const std::string str = ((const std::string)  tolua_tocppstring(tolua_S,2,0));
   self->initFromString(str);
   tolua_pushcppstring(tolua_S,(const char*)str);
}

Now,i want to pass binary data from lua to c++,the binary has ‘\0’ in it,so if i use initFromString to pass it, the binary data will be trimed. But if i use initFromBuffer to pass it, i got bad ptr at `void* buffer = ((void*) tolua_touserdata(tolua_S,2,0));, the pointer is null.

So, how could i pass binary string from lua to c++?

Answer 1

Maybe you should stop using Tolua’s bad APIs and use plain Lua’s actually good APIs. Both std::string and Lua strings are capable of storing embedded null characters. The only reason tolua_tocppstring causes truncation is because the function name is a lie. It doesn’t convert it to a C++ string; it converts it to a C string, a const char*.

The correct answer is to use the proper API function:

std::string fromLuaStack(lua_State *lua, int stackIx)
{
  size_t len;
  const char *str = lua_tolstring(lua, stackIx, &len);
  return std::string(str, len);
}

Similarly, you can use lua_pushlstring to push a std::string onto the stack.

It’s unfortunate that Tolua doesn’t have better documentation, as there may be a function to do this all directly. If there is, I couldn’t find it.