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Whenever a-c features is called, the upvalues are found at specific pseudo-indices

3.4 C Closures

When a-c function is made, you'll be able to connect some beliefs with-it, hence producing a C closing; these standards are known as upvalues and are available to the function anytime really called (see lua_pushcclosure ).

These pseudo-indices are produced because of the macro lua_upvalueindex . Initial price of a function reaches situation lua_upvalueindex(1) , etc. Any access to lua_upvalueindex(n) , in which n is greater than how many upvalues from the recent purpose (but not higher than 256), produces a satisfactory (but incorrect) index.

3.5 Registry

Lua supplies a registry, a pre-defined table you can use by any C code to save whatever Lua https://datingmentor.org/professional-dating-site/ price it must put. This dining table is always located at pseudo-index LUA_REGISTRYINDEX . Any C library can shop facts into this dining table, however it should take the time to select points different from those employed by some other libraries, in order to prevent collisions. Usually, you should utilize as important a string containing the library title or a light userdata because of the target of a-c object within rule.

The integer techniques for the registry are widely-used by research mechanism, implemented by the additional library, and for that reason really should not be employed for more needs.

3.6 Mistake Managing in C

Internally, Lua uses the C longjmp premises to manage mistakes. (You can also choose to use conditions if you are using C++; discover file luaconf.h .) Whenever Lua faces any error (such as for instance memories allocation mistakes, type errors, syntax problems, and runtime errors) it increases one; definitely, it can a long leap. A protected ecosystem utilizes setjmp to put a recover aim; any error jumps to the latest energetic recuperate aim.

Many functionality when you look at the API can toss a mistake, for example because a memory allowance error. The documentation for each purpose shows whether or not it can throw errors.