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In C++, I have a map<string, string>, containing an unknown number of entries. How can I pass this to a Lua function, so that the Lua function can use the data as a table?

hjpotter92
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Rocketmagnet
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2 Answers2

19

if you want a real lua table:

lua_newtable(L);
int top = lua_gettop(L);

for (std::map::iterator it = mymap.begin(); it != mymap.end(); ++it) {
    const char* key = it->first.c_str();
    const char* value = it->second.c_str();
    lua_pushlstring(L, key, it->first.size());
    lua_pushlstring(L, value, it->second.size());
    lua_settable(L, top);
}

with the right types for your map substituted in..

Nicol Bolas
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sean riley
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5

A couple options...

  1. Copy the map into a new Lua table, and pass the Lua table.

  2. Create a proxy table that directs reads and writes through a metatable's __index and __newindex metamethods

The drawback to (1) is all the copying, of course.

The drawback to (2) is that pairs() won't work on the proxy table

A discussion of fixes to Lua for generalized pairs is in the wiki and this mailing list thread. Generalized pairs is expected for Lua 5.2

Doug Currie
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  • It shouldn't be too difficult to add an iterator function to the metatable that can be used just like pairs() for tables. – David Hanak Jan 17 '09 at 18:51
  • i usually do option 2; unless the table is small and there's lots of requests to a mostly read-only table. – Javier Jan 17 '09 at 19:09