Wrong result after catch(...)

[jinq0123]

I am trying to catch exception from LuaRef::toValue().

#include <LuaIntf/LuaIntf.h>

using LuaIntf::LuaRef;

std::tuple<LuaRef, std::string> TestToStr(const LuaRef& luaVal)
{
    try{
        std::string s(luaVal.toValue<const char*>());
        return std::make_tuple(LuaRef::fromValue(
            luaVal.state(), "Hello, " + s), "OK");
    }
    catch(...)
    {
    }
    return std::make_tuple(LuaRef(luaVal.state(), nullptr), "Exception");
}

extern "C"
#if defined(_MSC_VER) || defined(__BORLANDC__) || defined(__CODEGEARC__)
__declspec(dllexport)
#endif
int luaopen_lfb(lua_State* L)
{
    using namespace LuaIntf;
    LuaRef mod = LuaRef::createTable(L);
    LuaBinding(mod)
        .addFunction("test_to_str", &TestToStr);
    mod.pushToStack();
    return 1;
}

But the result is wrong after catch.

E:\Git\Lua\lua-flatbuffers_jinq0123\test>lua53pp
Lua 5.3.2  Copyright (C) 1994-2015 Lua.org, PUC-Rio
> package.cpath = package.cpath .. ";../bin/Debug/?.dll"
> lfb = require("lfb")
> lfb.test_to_str(true)
Exception
>

Expected:

nil     Exception

Got:

Exception

Why?

Lua 5.3.2 is build as cpp.

More test:

> inspect = require("inspect")
> t = {lfb.test_to_str(true)}
(null)
> inspect(t)
{
  [2] = "Exception"
}
> t2 = {lfb.test_to_str(1234)}
> inspect(t2)
{ "Hello, 1234", "OK" }
>

[SteveKChiu]

It seems normal.

null is special, assign null to table will not create the entry.

try

err, desc = lfb.test_to_str(true)

to get the first arg.

[jinq0123]

Maybe it's the problem of Lua console.

If delete try/catch:

std::tuple<LuaRef, std::string> TestToStr(const LuaRef& luaVal)
{
    return std::make_tuple(LuaRef(luaVal.state(), nullptr), "Exception");
}

the console will output as expected:

> lfb.test_to_str(true)
nil     Exception

If any exception, the console outputs differently.

[jinq0123]

In lua.c:

/*
** Do the REPL: repeatedly read (load) a line, evaluate (call) it, and
** print any results.
*/
static void doREPL (lua_State *L) {
  ...
  while ((status = loadline(L)) != -1) {
    if (status == LUA_OK)
      status = docall(L, 0, LUA_MULTRET);
    if (status == LUA_OK) l_print(L);
    else report(L, status);
  }
  ...
}

If any exception happened, the status will be bad.