Using Lua to modify an XML string from C++

In my C++ app, I have a string which contains XML data. Let's say I have an attribute Number1 and an attribute Number2.

I want to send that string to a Lua script and have it return a mo开发者_开发知识库dified XML string. Let's say it adds a new attribute Product with the value of Number1 and Number2.

Is that easily done using C++/Lua, and if so how?

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There are several methods to work with XML data listed at the Lua Users Wiki. The better options involve calls back to C (e.g. LuaXML and LuaExpat) so this only makes sense to do if there are other reasons to use Lua beyond just parsing XML.

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Not a Lua user myself...but just browsing the documentation, it seems that you can use lua_pushstring() to put a copy of a null-terminated C string into the Lua stack:

http://pgl.yoyo.org/luai/i/lua_pushstring

Although there is no specific definition for things like lua_popstring() you can define something like that yourself:

std::string lua_popstring(lua_State *L)
{
    std::string tmp = lua_tostring(L, lua_gettop(L));
    lua_pop(L, 1);
    return tmp;
}

With that in hand you should be able to modify the standard example for passing data into Lua and getting a result back for your purpose:

http://lua-users.org/wiki/SimpleLuaApiExample

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You could do it similar to this (not this might not be 100 % correct due to being out of my mind and it doesn't include error handling):

lua_getglobal(L, "modifyXml"); // push function on stack by name
lua_pushstring(L, xml); // push the xml string as parameter
lua_pcall(L, 1, 1, 0); // call the function with 1 parameter, 1 return value and no error handler
strcpy(xml, lua_tostring(L, -1)); // get the top of the stack as a string and copy it to xml
lua_pop(xml, 1); // remove the string from the stack

The lua function called could look like this:

function modifyXml(xml)
    -- do something with xml here
    return xml
end

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If you use Luabind it could look something like this in C++:

std::string result = luabind::call_function<std::string>(
    "yourLuaFunction", inputXmlString);

You would implement yourLuaFunction in Lua of course, and require that Lua module from within your C++ program.