This page describes the API functions provided by the FFI library indetail. It's recommended to read through theintroduction and theFFI tutorial first.

Each function is as thin and fast an implementation as is possible within that host Lua environment, evaluating to the Lua C implementation with no overhead where host semantics allow. The core of this module is to transparently set the environment up with a single API (as opposed to requiring caching functions from a module table into module. Tables are the only data structure available in Lua that helps us create different types like arrays and dictionaries. Lua uses associative arrays and which can be indexed with not only numbers but also with strings except nil. Tables have no fixed size and can grow based on our need. Lua's standard library and most modules written for Lua assume 1 as the first index for sequences. A gapless array therefore has items from 1.n without missing any numbers in the sequence. (In the limiting case, n = 1, and the array has only one item in it.) Lua provides the built-in function ipairs to iterate over such tables.

Lua table(表) table 是 Lua 的一种数据结构用来帮助我们创建不同的数据类型，如：数组、字典等。 Lua table 使用关联型数组，你可以用任意类型的值来作数组的索引，但这个值不能是 nil。 Lua table 是不固定大小的，你可以根据自己需要进行扩容。 Lua也是通过table来解决模块（module）、包（package）和对.

Glossary

cdecl — An abstract C type declaration (a Luastring).
ctype — A C type object. This is a special kind ofcdata returned by ffi.typeof(). It serves as acdataconstructor when called.
cdata — A C data object. It holds a value of thecorresponding ctype.
ct — A C type specification which can be used formost of the API functions. Either a cdecl, a ctype or acdata serving as a template type.
cb — A callback object. This is a C data objectholding a special function pointer. Calling this function fromC code runs an associated Lua function.
VLA — A variable-length array is declared with a? instead of the number of elements, e.g. 'int[?]'.The number of elements (nelem) must be given when it'screated.
VLS — A variable-length struct is a struct Ctype where the last element is a VLA. The same rules fordeclaration and creation apply.

Declaring and Accessing External Symbols

External symbols must be declared first and can then be accessed byindexing a C librarynamespace, which automatically binds the symbol to a specificlibrary.

`ffi.cdef(def)`

Adds multiple C declarations for types or external symbols (namedvariables or functions). def must be a Lua string. It'srecommended to use the syntactic sugar for string arguments asfollows:

The contents of the string (the part in green above) must be asequence ofC declarations,separated by semicolons. The trailing semicolon for a singledeclaration may be omitted.

Please note that external symbols are only declared, but theyare not bound to any specific address, yet. Binding isachieved with C library namespaces (see below).

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C declarations are not passed through a C pre-processor,yet. No pre-processor tokens are allowed, except for#pragma pack. Replace #define in existingC header files with enum, static constor typedef and/or pass the files through an externalC pre-processor (once). Be careful not to include unneeded orredundant declarations from unrelated header files.

`ffi.C`

This is the default C library namespace — note theuppercase 'C'. It binds to the default set of symbols orlibraries on the target system. These are more or less the same as aC compiler would offer by default, without specifying extra linklibraries.

On POSIX systems, this binds to symbols in the default or globalnamespace. This includes all exported symbols from the executable andany libraries loaded into the global namespace. This includes at leastlibc, libm, libdl (on Linux),libgcc (if compiled with GCC), as well as any exportedsymbols from the Lua/C API provided by LuaJIT itself.

On Windows systems, this binds to symbols exported from the*.exe, the lua51.dll (i.e. the Lua/C APIprovided by LuaJIT itself), the C runtime library LuaJIT was linkedwith (msvcrt*.dll), kernel32.dll,user32.dll and gdi32.dll.

`clib = ffi.load(name [,global])`

This loads the dynamic library given by name and returnsa new C library namespace which binds to its symbols. On POSIXsystems, if global is true, the library symbols areloaded into the global namespace, too.

If name is a path, the library is loaded from this path.Otherwise name is canonicalized in a system-dependent way andsearched in the default search path for dynamic libraries:

On POSIX systems, if the name contains no dot, the extension.so is appended. Also, the lib prefix is prependedif necessary. So ffi.load('z') looks for 'libz.so'in the default shared library search path.

On Windows systems, if the name contains no dot, the extension.dll is appended. So ffi.load('ws2_32') looks for'ws2_32.dll' in the default DLL search path.

Creating cdata Objects

The following API functions create cdata objects (type()returns 'cdata'). All created cdata objects aregarbage collected.

`cdata = ffi.new(ct [,nelem] [,init..]) cdata = ctype([nelem,] [init..])`

Creates a cdata object for the given ct. VLA/VLS typesrequire the nelem argument. The second syntax uses a ctype asa constructor and is otherwise fully equivalent.

The cdata object is initialized according to therules for initializers,using the optional init arguments. Download the middle finger emoji. Excess initializers causean error.

Performance notice: if you want to create many objects of one kind,parse the cdecl only once and get its ctype withffi.typeof(). Then use the ctype as a constructor repeatedly.

Please note that an anonymous struct declaration implicitlycreates a new and distinguished ctype every time you use it forffi.new(). This is probably not what you want,especially if you create more than one cdata object. Different anonymousstructs are not considered assignment-compatible by theC standard, even though they may have the same fields! Also, theyare considered different types by the JIT-compiler, which may cause anexcessive number of traces. It's strongly suggested to either declarea named struct or typedef with ffi.cdef()or to create a single ctype object for an anonymous structwith ffi.typeof().

`ctype = ffi.typeof(ct)`

Creates a ctype object for the given ct.

This function is especially useful to parse a cdecl only once and thenuse the resulting ctype object as a constructor.

`cdata = ffi.cast(ct, init)`

Lua Table Contains Key

Creates a scalar cdata object for the given ct. The cdataobject is initialized with init using the 'cast' variant ofthe C type conversionrules.

This functions is mainly useful to override the pointer compatibilitychecks or to convert pointers to addresses or vice versa.

`ctype = ffi.metatype(ct, metatable)`

Creates a ctype object for the given ct and associates it witha metatable. Only struct/union types, complex numbersand vectors are allowed. Other types may be wrapped in astruct, if needed.

The association with a metatable is permanent and cannot be changedafterwards. Neither the contents of the metatable nor thecontents of an __index table (if any) may be modifiedafterwards. The associated metatable automatically applies to all usesof this type, no matter how the objects are created or where theyoriginate from. Note that pre-defined operations on types haveprecedence (e.g. declared field names cannot be overridden).

All standard Lua metamethods are implemented. These are called directly,without shortcuts and on any mix of types. For binary operations, theleft operan

Glossary

Declaring and Accessing External Symbols

ffi.cdef(def)

ffi.C

clib = ffi.load(name [,global])

Creating cdata Objects

cdata = ffi.new(ct [,nelem] [,init..])cdata = ctype([nelem,] [init..])

ctype = ffi.typeof(ct)

cdata = ffi.cast(ct, init)

Lua C Api Get Table Key