3.4 C Closures

When a C function is created, it is possible to connect some standards with-it, therefore generating a C closure; these values have been called upvalues and are available to the big event whenever it's also known as (discover lua_pushcclosure ).

These pseudo-indices are produced from the macro lua_upvalueindex . The most important appreciate involving a function is at situation lua_upvalueindex(1) , an such like. Any use of lua_upvalueindex(letter) , in which letter is more than the sheer number of upvalues with the present function (but not higher than 256), generates an acceptable (but incorrect) list.

3.5 Registry

Lua produces a registry, a pre-defined dining table which you can use by any C laws to save whatever Lua importance it needs to put. This dining table is always found at pseudo-index LUA_REGISTRYINDEX . Any C collection can shop information into this table, nevertheless should take time to determine secrets different from those used by some other libraries, in order to prevent crashes. Typically, you need to use as important a string that contain your library name or a light userdata utilizing the address of a-c item inside code.

The integer tactics when you look at the registry are employed of the guide mechanism, applied by the additional collection, therefore shouldn't be useful some other needs.

3.6 Mistake Handling in C

Internally, Lua utilizes the C longjmp facility to carry out problems. (It is possible to go for exceptions when you use C++; discover document luaconf.h .) Whenever Lua faces any error (such as for instance storage allocation errors, type problems, syntax problems, and runtime errors) it increases a mistake; which, it can a lengthy hop. A protected planet utilizes setjmp to put a recover aim; any error jumps into most recent productive recover point.

Many features inside API can toss one, such as due to a storage allocation error. The documents for each and every function show whether it can throw mistakes.

3.7 Applications and Types

Right here we identify all features and kinds from C API in alphabetical order. Each purpose provides an indicator such as this: [-o, +p, x]

1st industry, o , are exactly how many aspects the event pops from pile. The 2nd field, p , is actually the number of elements the big event forces on the pile. (Any purpose always forces its outcomes after popping their arguments.) A field during the kind x|y implies the big event can force (or pop) x or y items, depending on the situation; an interrogation level ' ? ' implies that we simply cannot understand how a lot of characteristics the function pops/pushes by searching just at its arguments (elizabeth.g., they could rely on something regarding heap). The next field, x , tells perhaps the work may throw errors: ' - ' ways the function never tosses any error; ' m ' ways the function may put one only due to not enough memory; ' e ' suggests the big event may toss other kinds of errors; ' v ' implies the function may place a mistake deliberately.

lua_Alloc

The sort of the memory-allocation features utilized by Lua says. The allocator function must definitely provide a functionality much like realloc , yet not precisely the same. The arguments become ud , an opaque pointer passed to lua_newstate ; ptr , a pointer for the block are allocated/reallocated/freed; osize , the initial sized the block; nsize , new measurements of the block. ptr are NULL if and just if osize are zero. When nsize try zero, the allocator must go back NULL ; if osize is not zero, it ought to release the block directed to by ptr . Whenever nsize is certainly not zero, the allocator return NULL if and simply if this cannot fill the request. Whenever nsize just isn't zero and osize is actually zero, the allocator should act love malloc . Whenever nsize and osize aren't zero, the allocator behaves like realloc . Lua assumes that allocator never ever fails when osize >= nsize .