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571 lines
21 KiB
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<title>ffi.* API Functions</title>
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<meta name="Author" content="Mike Pall">
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<a href="http://luajit.org"><span>Lua<span id="logo">JIT</span></span></a>
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<div id="head">
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<h1><tt>ffi.*</tt> API Functions</h1>
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<div id="main">
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<p>
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This page describes the API functions provided by the FFI library in
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detail. It's recommended to read through the
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<a href="ext_ffi.html">introduction</a> and the
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<a href="ext_ffi_tutorial.html">FFI tutorial</a> first.
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</p>
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<h2 id="glossary">Glossary</h2>
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<ul>
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<li><b>cdecl</b> — An abstract C type declaration (a Lua
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string).</li>
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<li><b>ctype</b> — A C type object. This is a special kind of
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<b>cdata</b> returned by <tt>ffi.typeof()</tt>. It serves as a
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<b>cdata</b> <a href="#ffi_new">constructor</a> when called.</li>
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<li><b>cdata</b> — A C data object. It holds a value of the
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corresponding <b>ctype</b>.</li>
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<li><b>ct</b> — A C type specification which can be used for
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most of the API functions. Either a <b>cdecl</b>, a <b>ctype</b> or a
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<b>cdata</b> serving as a template type.</li>
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<li><b>cb</b> — A callback object. This is a C data object
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holding a special function pointer. Calling this function from
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C code runs an associated Lua function.</li>
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<li><b>VLA</b> — A variable-length array is declared with a
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<tt>?</tt> instead of the number of elements, e.g. <tt>"int[?]"</tt>.
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The number of elements (<tt>nelem</tt>) must be given when it's
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<a href="#ffi_new">created</a>.</li>
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<li><b>VLS</b> — A variable-length struct is a <tt>struct</tt> C
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type where the last element is a <b>VLA</b>. The same rules for
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declaration and creation apply.</li>
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</ul>
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<h2 id="decl">Declaring and Accessing External Symbols</h2>
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<p>
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External symbols must be declared first and can then be accessed by
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indexing a <a href="ext_ffi_semantics.html#clib">C library
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namespace</a>, which automatically binds the symbol to a specific
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library.
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</p>
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<h3 id="ffi_cdef"><tt>ffi.cdef(def)</tt></h3>
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<p>
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Adds multiple C declarations for types or external symbols (named
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variables or functions). <tt>def</tt> must be a Lua string. It's
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recommended to use the syntactic sugar for string arguments as
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follows:
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</p>
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<pre class="code">
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ffi.cdef[[
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<span style="color:#00a000;">typedef struct foo { int a, b; } foo_t; // Declare a struct and typedef.
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int dofoo(foo_t *f, int n); /* Declare an external C function. */</span>
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]]
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</pre>
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<p>
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The contents of the string (the part in green above) must be a
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sequence of
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<a href="ext_ffi_semantics.html#clang">C declarations</a>,
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separated by semicolons. The trailing semicolon for a single
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declaration may be omitted.
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</p>
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<p>
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Please note that external symbols are only <em>declared</em>, but they
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are <em>not bound</em> to any specific address, yet. Binding is
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achieved with C library namespaces (see below).
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</p>
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<p style="color: #c00000;">
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C declarations are not passed through a C pre-processor,
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yet. No pre-processor tokens are allowed, except for
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<tt>#pragma pack</tt>. Replace <tt>#define</tt> in existing
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C header files with <tt>enum</tt>, <tt>static const</tt>
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or <tt>typedef</tt> and/or pass the files through an external
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C pre-processor (once). Be careful not to include unneeded or
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redundant declarations from unrelated header files.
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</p>
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<h3 id="ffi_C"><tt>ffi.C</tt></h3>
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<p>
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This is the default C library namespace — note the
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uppercase <tt>'C'</tt>. It binds to the default set of symbols or
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libraries on the target system. These are more or less the same as a
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C compiler would offer by default, without specifying extra link
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libraries.
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</p>
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<p>
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On POSIX systems, this binds to symbols in the default or global
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namespace. This includes all exported symbols from the executable and
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any libraries loaded into the global namespace. This includes at least
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<tt>libc</tt>, <tt>libm</tt>, <tt>libdl</tt> (on Linux),
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<tt>libgcc</tt> (if compiled with GCC), as well as any exported
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symbols from the Lua/C API provided by LuaJIT itself.
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</p>
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<p>
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On Windows systems, this binds to symbols exported from the
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<tt>*.exe</tt>, the <tt>lua51.dll</tt> (i.e. the Lua/C API
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provided by LuaJIT itself), the C runtime library LuaJIT was linked
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with (<tt>msvcrt*.dll</tt>), <tt>kernel32.dll</tt>,
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<tt>user32.dll</tt> and <tt>gdi32.dll</tt>.
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</p>
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<h3 id="ffi_load"><tt>clib = ffi.load(name [,global])</tt></h3>
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<p>
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This loads the dynamic library given by <tt>name</tt> and returns
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a new C library namespace which binds to its symbols. On POSIX
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systems, if <tt>global</tt> is <tt>true</tt>, the library symbols are
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loaded into the global namespace, too.
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</p>
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<p>
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If <tt>name</tt> is a path, the library is loaded from this path.
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Otherwise <tt>name</tt> is canonicalized in a system-dependent way and
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searched in the default search path for dynamic libraries:
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</p>
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<p>
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On POSIX systems, if the name contains no dot, the extension
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<tt>.so</tt> is appended. Also, the <tt>lib</tt> prefix is prepended
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if necessary. So <tt>ffi.load("z")</tt> looks for <tt>"libz.so"</tt>
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in the default shared library search path.
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</p>
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<p>
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On Windows systems, if the name contains no dot, the extension
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<tt>.dll</tt> is appended. So <tt>ffi.load("ws2_32")</tt> looks for
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<tt>"ws2_32.dll"</tt> in the default DLL search path.
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</p>
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<h2 id="create">Creating cdata Objects</h2>
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<p>
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The following API functions create cdata objects (<tt>type()</tt>
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returns <tt>"cdata"</tt>). All created cdata objects are
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<a href="ext_ffi_semantics.html#gc">garbage collected</a>.
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</p>
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<h3 id="ffi_new"><tt>cdata = ffi.new(ct [,nelem] [,init...])<br>
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cdata = <em>ctype</em>([nelem,] [init...])</tt></h3>
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<p>
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Creates a cdata object for the given <tt>ct</tt>. VLA/VLS types
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require the <tt>nelem</tt> argument. The second syntax uses a ctype as
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a constructor and is otherwise fully equivalent.
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</p>
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<p>
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The cdata object is initialized according to the
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<a href="ext_ffi_semantics.html#init">rules for initializers</a>,
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using the optional <tt>init</tt> arguments. Excess initializers cause
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an error.
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</p>
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<p>
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Performance notice: if you want to create many objects of one kind,
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parse the cdecl only once and get its ctype with
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<tt>ffi.typeof()</tt>. Then use the ctype as a constructor repeatedly.
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</p>
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<p style="font-size: 8pt;">
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Please note that an anonymous <tt>struct</tt> declaration implicitly
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creates a new and distinguished ctype every time you use it for
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<tt>ffi.new()</tt>. This is probably <b>not</b> what you want,
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especially if you create more than one cdata object. Different anonymous
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<tt>structs</tt> are not considered assignment-compatible by the
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C standard, even though they may have the same fields! Also, they
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are considered different types by the JIT-compiler, which may cause an
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excessive number of traces. It's strongly suggested to either declare
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a named <tt>struct</tt> or <tt>typedef</tt> with <tt>ffi.cdef()</tt>
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or to create a single ctype object for an anonymous <tt>struct</tt>
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with <tt>ffi.typeof()</tt>.
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</p>
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<h3 id="ffi_typeof"><tt>ctype = ffi.typeof(ct)</tt></h3>
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<p>
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Creates a ctype object for the given <tt>ct</tt>.
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</p>
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<p>
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This function is especially useful to parse a cdecl only once and then
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use the resulting ctype object as a <a href="#ffi_new">constructor</a>.
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</p>
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<h3 id="ffi_cast"><tt>cdata = ffi.cast(ct, init)</tt></h3>
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<p>
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Creates a scalar cdata object for the given <tt>ct</tt>. The cdata
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object is initialized with <tt>init</tt> using the "cast" variant of
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the <a href="ext_ffi_semantics.html#convert">C type conversion
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rules</a>.
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</p>
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<p>
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This functions is mainly useful to override the pointer compatibility
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checks or to convert pointers to addresses or vice versa.
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</p>
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<h3 id="ffi_metatype"><tt>ctype = ffi.metatype(ct, metatable)</tt></h3>
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<p>
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Creates a ctype object for the given <tt>ct</tt> and associates it with
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a metatable. Only <tt>struct</tt>/<tt>union</tt> types, complex numbers
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and vectors are allowed. Other types may be wrapped in a
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<tt>struct</tt>, if needed.
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</p>
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<p>
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The association with a metatable is permanent and cannot be changed
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afterwards. Neither the contents of the <tt>metatable</tt> nor the
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contents of an <tt>__index</tt> table (if any) may be modified
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afterwards. The associated metatable automatically applies to all uses
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of this type, no matter how the objects are created or where they
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originate from. Note that pre-defined operations on types have
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precedence (e.g. declared field names cannot be overriden).
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</p>
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<p>
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All standard Lua metamethods are implemented. These are called directly,
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without shortcuts and on any mix of types. For binary operations, the
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left operand is checked first for a valid ctype metamethod. The
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<tt>__gc</tt> metamethod only applies to <tt>struct</tt>/<tt>union</tt>
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types and performs an implicit <a href="#ffi_gc"><tt>ffi.gc()</tt></a>
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call during creation of an instance.
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</p>
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<h3 id="ffi_gc"><tt>cdata = ffi.gc(cdata, finalizer)</tt></h3>
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<p>
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Associates a finalizer with a pointer or aggregate cdata object. The
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cdata object is returned unchanged.
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</p>
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<p>
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This function allows safe integration of unmanaged resources into the
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automatic memory management of the LuaJIT garbage collector. Typical
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usage:
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</p>
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<pre class="code">
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local p = ffi.gc(ffi.C.malloc(n), ffi.C.free)
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...
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p = nil -- Last reference to p is gone.
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-- GC will eventually run finalizer: ffi.C.free(p)
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</pre>
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<p>
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A cdata finalizer works like the <tt>__gc</tt> metamethod for userdata
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objects: when the last reference to a cdata object is gone, the
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associated finalizer is called with the cdata object as an argument. The
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finalizer can be a Lua function or a cdata function or cdata function
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pointer. An existing finalizer can be removed by setting a <tt>nil</tt>
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finalizer, e.g. right before explicitly deleting a resource:
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</p>
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<pre class="code">
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ffi.C.free(ffi.gc(p, nil)) -- Manually free the memory.
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</pre>
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<h2 id="info">C Type Information</h2>
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<p>
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The following API functions return information about C types.
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They are most useful for inspecting cdata objects.
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</p>
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<h3 id="ffi_sizeof"><tt>size = ffi.sizeof(ct [,nelem])</tt></h3>
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<p>
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Returns the size of <tt>ct</tt> in bytes. Returns <tt>nil</tt> if
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the size is not known (e.g. for <tt>"void"</tt> or function types).
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Requires <tt>nelem</tt> for VLA/VLS types, except for cdata objects.
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</p>
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<h3 id="ffi_alignof"><tt>align = ffi.alignof(ct)</tt></h3>
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<p>
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Returns the minimum required alignment for <tt>ct</tt> in bytes.
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</p>
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<h3 id="ffi_offsetof"><tt>ofs [,bpos,bsize] = ffi.offsetof(ct, field)</tt></h3>
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<p>
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Returns the offset (in bytes) of <tt>field</tt> relative to the start
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of <tt>ct</tt>, which must be a <tt>struct</tt>. Additionally returns
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the position and the field size (in bits) for bit fields.
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</p>
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<h3 id="ffi_istype"><tt>status = ffi.istype(ct, obj)</tt></h3>
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<p>
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Returns <tt>true</tt> if <tt>obj</tt> has the C type given by
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<tt>ct</tt>. Returns <tt>false</tt> otherwise.
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</p>
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<p>
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C type qualifiers (<tt>const</tt> etc.) are ignored. Pointers are
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checked with the standard pointer compatibility rules, but without any
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special treatment for <tt>void *</tt>. If <tt>ct</tt> specifies a
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<tt>struct</tt>/<tt>union</tt>, then a pointer to this type is accepted,
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too. Otherwise the types must match exactly.
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</p>
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<p>
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Note: this function accepts all kinds of Lua objects for the
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<tt>obj</tt> argument, but always returns <tt>false</tt> for non-cdata
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objects.
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</p>
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<h2 id="util">Utility Functions</h2>
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<h3 id="ffi_errno"><tt>err = ffi.errno([newerr])</tt></h3>
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<p>
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Returns the error number set by the last C function call which
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indicated an error condition. If the optional <tt>newerr</tt> argument
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is present, the error number is set to the new value and the previous
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value is returned.
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</p>
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<p>
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This function offers a portable and OS-independent way to get and set the
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error number. Note that only <em>some</em> C functions set the error
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number. And it's only significant if the function actually indicated an
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error condition (e.g. with a return value of <tt>-1</tt> or
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<tt>NULL</tt>). Otherwise, it may or may not contain any previously set
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value.
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</p>
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<p>
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You're advised to call this function only when needed and as close as
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possible after the return of the related C function. The
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<tt>errno</tt> value is preserved across hooks, memory allocations,
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invocations of the JIT compiler and other internal VM activity. The same
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applies to the value returned by <tt>GetLastError()</tt> on Windows, but
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you need to declare and call it yourself.
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</p>
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<h3 id="ffi_string"><tt>str = ffi.string(ptr [,len])</tt></h3>
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<p>
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Creates an interned Lua string from the data pointed to by
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<tt>ptr</tt>.
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</p>
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<p>
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If the optional argument <tt>len</tt> is missing, <tt>ptr</tt> is
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converted to a <tt>"char *"</tt> and the data is assumed to be
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zero-terminated. The length of the string is computed with
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<tt>strlen()</tt>.
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</p>
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<p>
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Otherwise <tt>ptr</tt> is converted to a <tt>"void *"</tt> and
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<tt>len</tt> gives the length of the data. The data may contain
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embedded zeros and need not be byte-oriented (though this may cause
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endianess issues).
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</p>
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<p>
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This function is mainly useful to convert (temporary)
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<tt>"const char *"</tt> pointers returned by
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C functions to Lua strings and store them or pass them to other
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functions expecting a Lua string. The Lua string is an (interned) copy
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of the data and bears no relation to the original data area anymore.
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Lua strings are 8 bit clean and may be used to hold arbitrary,
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non-character data.
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</p>
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<p>
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Performance notice: it's faster to pass the length of the string, if
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it's known. E.g. when the length is returned by a C call like
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<tt>sprintf()</tt>.
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</p>
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<h3 id="ffi_copy"><tt>ffi.copy(dst, src, len)<br>
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ffi.copy(dst, str)</tt></h3>
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<p>
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Copies the data pointed to by <tt>src</tt> to <tt>dst</tt>.
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<tt>dst</tt> is converted to a <tt>"void *"</tt> and <tt>src</tt>
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is converted to a <tt>"const void *"</tt>.
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</p>
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<p>
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In the first syntax, <tt>len</tt> gives the number of bytes to copy.
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Caveat: if <tt>src</tt> is a Lua string, then <tt>len</tt> must not
|
|
exceed <tt>#src+1</tt>.
|
|
</p>
|
|
<p>
|
|
In the second syntax, the source of the copy must be a Lua string. All
|
|
bytes of the string <em>plus a zero-terminator</em> are copied to
|
|
<tt>dst</tt> (i.e. <tt>#src+1</tt> bytes).
|
|
</p>
|
|
<p>
|
|
Performance notice: <tt>ffi.copy()</tt> may be used as a faster
|
|
(inlinable) replacement for the C library functions
|
|
<tt>memcpy()</tt>, <tt>strcpy()</tt> and <tt>strncpy()</tt>.
|
|
</p>
|
|
|
|
<h3 id="ffi_fill"><tt>ffi.fill(dst, len [,c])</tt></h3>
|
|
<p>
|
|
Fills the data pointed to by <tt>dst</tt> with <tt>len</tt> constant
|
|
bytes, given by <tt>c</tt>. If <tt>c</tt> is omitted, the data is
|
|
zero-filled.
|
|
</p>
|
|
<p>
|
|
Performance notice: <tt>ffi.fill()</tt> may be used as a faster
|
|
(inlinable) replacement for the C library function
|
|
<tt>memset(dst, c, len)</tt>. Please note the different
|
|
order of arguments!
|
|
</p>
|
|
|
|
<h2 id="target">Target-specific Information</h2>
|
|
|
|
<h3 id="ffi_abi"><tt>status = ffi.abi(param)</tt></h3>
|
|
<p>
|
|
Returns <tt>true</tt> if <tt>param</tt> (a Lua string) applies for the
|
|
target ABI (Application Binary Interface). Returns <tt>false</tt>
|
|
otherwise. The following parameters are currently defined:
|
|
</p>
|
|
<table class="abitable">
|
|
<tr class="abihead">
|
|
<td class="abiparam">Parameter</td>
|
|
<td class="abidesc">Description</td>
|
|
</tr>
|
|
<tr class="odd separate">
|
|
<td class="abiparam">32bit</td><td class="abidesc">32 bit architecture</td></tr>
|
|
<tr class="even">
|
|
<td class="abiparam">64bit</td><td class="abidesc">64 bit architecture</td></tr>
|
|
<tr class="odd separate">
|
|
<td class="abiparam">le</td><td class="abidesc">Little-endian architecture</td></tr>
|
|
<tr class="even">
|
|
<td class="abiparam">be</td><td class="abidesc">Big-endian architecture</td></tr>
|
|
<tr class="odd separate">
|
|
<td class="abiparam">fpu</td><td class="abidesc">Target has a hardware FPU</td></tr>
|
|
<tr class="even">
|
|
<td class="abiparam">softfp</td><td class="abidesc">softfp calling conventions</td></tr>
|
|
<tr class="odd">
|
|
<td class="abiparam">hardfp</td><td class="abidesc">hardfp calling conventions</td></tr>
|
|
<tr class="even separate">
|
|
<td class="abiparam">eabi</td><td class="abidesc">EABI variant of the standard ABI</td></tr>
|
|
<tr class="odd">
|
|
<td class="abiparam">win</td><td class="abidesc">Windows variant of the standard ABI</td></tr>
|
|
<tr class="even">
|
|
<td class="abiparam">gc64</td><td class="abidesc">64 bit GC references</td></tr>
|
|
</table>
|
|
|
|
<h3 id="ffi_os"><tt>ffi.os</tt></h3>
|
|
<p>
|
|
Contains the target OS name. Same contents as
|
|
<a href="ext_jit.html#jit_os"><tt>jit.os</tt></a>.
|
|
</p>
|
|
|
|
<h3 id="ffi_arch"><tt>ffi.arch</tt></h3>
|
|
<p>
|
|
Contains the target architecture name. Same contents as
|
|
<a href="ext_jit.html#jit_arch"><tt>jit.arch</tt></a>.
|
|
</p>
|
|
|
|
<h2 id="callback">Methods for Callbacks</h2>
|
|
<p>
|
|
The C types for <a href="ext_ffi_semantics.html#callback">callbacks</a>
|
|
have some extra methods:
|
|
</p>
|
|
|
|
<h3 id="callback_free"><tt>cb:free()</tt></h3>
|
|
<p>
|
|
Free the resources associated with a callback. The associated Lua
|
|
function is unanchored and may be garbage collected. The callback
|
|
function pointer is no longer valid and must not be called anymore
|
|
(it may be reused by a subsequently created callback).
|
|
</p>
|
|
|
|
<h3 id="callback_set"><tt>cb:set(func)</tt></h3>
|
|
<p>
|
|
Associate a new Lua function with a callback. The C type of the
|
|
callback and the callback function pointer are unchanged.
|
|
</p>
|
|
<p>
|
|
This method is useful to dynamically switch the receiver of callbacks
|
|
without creating a new callback each time and registering it again (e.g.
|
|
with a GUI library).
|
|
</p>
|
|
|
|
<h2 id="extended">Extended Standard Library Functions</h2>
|
|
<p>
|
|
The following standard library functions have been extended to work
|
|
with cdata objects:
|
|
</p>
|
|
|
|
<h3 id="tonumber"><tt>n = tonumber(cdata)</tt></h3>
|
|
<p>
|
|
Converts a number cdata object to a <tt>double</tt> and returns it as
|
|
a Lua number. This is particularly useful for boxed 64 bit
|
|
integer values. Caveat: this conversion may incur a precision loss.
|
|
</p>
|
|
|
|
<h3 id="tostring"><tt>s = tostring(cdata)</tt></h3>
|
|
<p>
|
|
Returns a string representation of the value of 64 bit integers
|
|
(<tt><b>"</b>nnn<b>LL"</b></tt> or <tt><b>"</b>nnn<b>ULL"</b></tt>) or
|
|
complex numbers (<tt><b>"</b>re±im<b>i"</b></tt>). Otherwise
|
|
returns a string representation of the C type of a ctype object
|
|
(<tt><b>"ctype<</b>type<b>>"</b></tt>) or a cdata object
|
|
(<tt><b>"cdata<</b>type<b>>: </b>address"</tt>), unless you
|
|
override it with a <tt>__tostring</tt> metamethod (see
|
|
<a href="#ffi_metatype"><tt>ffi.metatype()</tt></a>).
|
|
</p>
|
|
|
|
<h3 id="pairs"><tt>iter, obj, start = pairs(cdata)<br>
|
|
iter, obj, start = ipairs(cdata)<br></tt></h3>
|
|
<p>
|
|
Calls the <tt>__pairs</tt> or <tt>__ipairs</tt> metamethod of the
|
|
corresponding ctype.
|
|
</p>
|
|
|
|
<h2 id="literals">Extensions to the Lua Parser</h2>
|
|
<p>
|
|
The parser for Lua source code treats numeric literals with the
|
|
suffixes <tt>LL</tt> or <tt>ULL</tt> as signed or unsigned 64 bit
|
|
integers. Case doesn't matter, but uppercase is recommended for
|
|
readability. It handles decimal (<tt>42LL</tt>), hexadecimal
|
|
(<tt>0x2aLL</tt>) and binary (<tt>0b101010LL</tt>) literals.
|
|
</p>
|
|
<p>
|
|
The imaginary part of complex numbers can be specified by suffixing
|
|
number literals with <tt>i</tt> or <tt>I</tt>, e.g. <tt>12.5i</tt>.
|
|
Caveat: you'll need to use <tt>1i</tt> to get an imaginary part with
|
|
the value one, since <tt>i</tt> itself still refers to a variable
|
|
named <tt>i</tt>.
|
|
</p>
|
|
<br class="flush">
|
|
</div>
|
|
<div id="foot">
|
|
<hr class="hide">
|
|
Copyright © 2005-2017 Mike Pall
|
|
<span class="noprint">
|
|
·
|
|
<a href="contact.html">Contact</a>
|
|
</span>
|
|
</div>
|
|
</body>
|
|
</html>
|