4.8 – Functions and Types

Here we list all functions and types from the C API in alphabetical order. Each function has an indicator like this: [-o, +p, x]

The first field, o, is how many elements the function pops from the stack. The second field, p, is how many elements the function pushes onto the stack. (Any function always pushes its results after popping its arguments.) A field in the form x|y means the function can push (or pop) x or y elements, depending on the situation; an interrogation mark ‘?‘ means that we cannot know how many elements the function pops/pushes by looking only at its arguments (e.g., they may depend on what is on the stack). The third field, x, tells whether the function may throw errors: ‘-‘ means the function never throws any error; ‘e‘ means the function may throw errors; ‘v‘ means the function may throw an error on purpose.

lua_absindex

[-0, +0, –]

int lua_absindex (lua_State *L, int idx);

Converts the acceptable index idx into an absolute index (that is, one that does not depend on the stack top).

lua_Alloc

typedef void * (*lua_Alloc) (void *ud,
                             void *ptr,
                             size_t osize,
                             size_t nsize);

The type of the memory-allocation function used by Lua states. The allocator function must provide a functionality similar to realloc, but not exactly the same. Its arguments are ud, an opaque pointer passed to lua_newstate; ptr, a pointer to the block being allocated/reallocated/freed; osize, the original size of the block or some code about what is being allocated; nsize, the new size of the block.

When ptr is not NULL, osize is the size of the block pointed by ptr, that is, the size given when it was allocated or reallocated.

When ptr is NULL, osize encodes the kind of object that Lua is allocating. osize is any of LUA_TSTRING, LUA_TTABLE, LUA_TFUNCTION, LUA_TUSERDATA, or LUA_TTHREAD when (and only when) Lua is creating a new object of that type. When osize is some other value, Lua is allocating memory for something else.

Lua assumes the following behavior from the allocator function:

When nsize is zero, the allocator should behave like free and return NULL.

When nsize is not zero, the allocator should behave like realloc. The allocator returns NULL if and only if it cannot fulfill the request. Lua assumes that the allocator never fails when osize >= nsize.

Here is a simple implementation for the allocator function. It is used in the auxiliary library by luaL_newstate.

     static void *l_alloc (void *ud, void *ptr, size_t osize,
                                                size_t nsize) {
       (void)ud;  (void)osize;  /* not used */
       if (nsize == 0) {
         free(ptr);
         return NULL;
       }
       else
         return realloc(ptr, nsize);
     }

Note that Standard C ensures that free(NULL) has no effect and that realloc(NULL, size) is equivalent to malloc(size). This code assumes that realloc does not fail when shrinking a block. (Although Standard C does not ensure this behavior, it seems to be a safe assumption.)

lua_arith

[-(2|1), +1, e]

void lua_arith (lua_State *L, int op);

Performs an arithmetic operation over the two values (or one, in the case of negation) at the top of the stack, with the value at the top being the second operand, pops these values, and pushes the result of the operation. The function follows the semantics of the corresponding Lua operator (that is, it may call metamethods).

The value of op must be one of the following constants:

• LUA_OPADD: performs addition (+)
• LUA_OPSUB: performs subtraction (-)
• LUA_OPMUL: performs multiplication (*)
• LUA_OPDIV: performs division (/)
• LUA_OPMOD: performs modulo (%)
• LUA_OPPOW: performs exponentiation (^)
• LUA_OPUNM: performs mathematical negation (unary -)

lua_atpanic

[-0, +0, –]

lua_CFunction lua_atpanic (lua_State *L, lua_CFunction panicf);

Sets a new panic function and returns the old one (see §4.6).

lua_call

[-(nargs+1), +nresults, e]

void lua_call (lua_State *L, int nargs, int nresults);

Calls a function.

To call a function you must use the following protocol: first, the function to be called is pushed onto the stack; then, the arguments to the function are pushed in direct order; that is, the first argument is pushed first. Finally you call lua_call; nargs is the number of arguments that you pushed onto the stack. All arguments and the function value are popped from the stack when the function is called. The function results are pushed onto the stack when the function returns. The number of results is adjusted to nresults, unless nresults is LUA_MULTRET. In this case, all results from the function are pushed. Lua takes care that the returned values fit into the stack space. The function results are pushed onto the stack in direct order (the first result is pushed first), so that after the call the last result is on the top of the stack.

Any error inside the called function is propagated upwards (with a longjmp).

The following example shows how the host program can do the equivalent to this Lua code:

     a = f("how", t.x, 14)

Here it is in C:

     lua_getglobal(L, "f");                  /* function to be called */
     lua_pushstring(L, "how");                        /* 1st argument */
     lua_getglobal(L, "t");                    /* table to be indexed */
     lua_getfield(L, -1, "x");        /* push result of t.x (2nd arg) */
     lua_remove(L, -2);                  /* remove 't' from the stack */
     lua_pushinteger(L, 14);                          /* 3rd argument */
     lua_call(L, 3, 1);     /* call 'f' with 3 arguments and 1 result */
     lua_setglobal(L, "a");                         /* set global 'a' */

Note that the code above is “balanced”: at its end, the stack is back to its original configuration. This is considered good programming practice.

lua_callk

[-(nargs + 1), +nresults, e]

void lua_callk (lua_State *L, int nargs, int nresults, int ctx,
                lua_CFunction k);

This function behaves exactly like lua_call, but allows the called function to yield (see §4.7).

lua_CFunction

typedef int (*lua_CFunction) (lua_State *L);

Type for C functions.

In order to communicate properly with Lua, a C function must use the following protocol, which defines the way parameters and results are passed: a C function receives its arguments from Lua in its stack in direct order (the first argument is pushed first). So, when the function starts, lua_gettop(L) returns the number of arguments received by the function. The first argument (if any) is at index 1 and its last argument is at index lua_gettop(L). To return values to Lua, a C function just pushes them onto the stack, in direct order (the first result is pushed first), and returns the number of results. Any other value in the stack below the results will be properly discarded by Lua. Like a Lua function, a C function called by Lua can also return many results.

As an example, the following function receives a variable number of numerical arguments and returns their average and sum:

     static int foo (lua_State *L) {
       int n = lua_gettop(L);    /* number of arguments */
       lua_Number sum = 0;
       int i;
       for (i = 1; i <= n; i++) {
         if (!lua_isnumber(L, i)) {
           lua_pushstring(L, "incorrect argument");
           lua_error(L);
         }
         sum += lua_tonumber(L, i);
       }
       lua_pushnumber(L, sum/n);        /* first result */
       lua_pushnumber(L, sum);         /* second result */
       return 2;                   /* number of results */
     }

lua_checkstack

[-0, +0, –]

int lua_checkstack (lua_State *L, int extra);

Ensures that there are at least extra free stack slots in the stack. It returns false if it cannot fulfill the request, because it would cause the stack to be larger than a fixed maximum size (typically at least a few thousand elements) or because it cannot allocate memory for the new stack size. This function never shrinks the stack; if the stack is already larger than the new size, it is left unchanged.

lua_close

[-0, +0, –]

void lua_close (lua_State *L);

Destroys all objects in the given Lua state (calling the corresponding garbage-collection metamethods, if any) and frees all dynamic memory used by this state. On several platforms, you may not need to call this function, because all resources are naturally released when the host program ends. On the other hand, long-running programs that create multiple states, such as daemons or web servers, might need to close states as soon as they are not needed.

lua_compare

[-0, +0, e]

int lua_compare (lua_State *L, int index1, int index2, int op);

Compares two Lua values. Returns 1 if the value at index index1 satisfies op when compared with the value at index index2, following the semantics of the corresponding Lua operator (that is, it may call metamethods). Otherwise returns 0. Also returns 0 if any of the indices is non valid.

The value of op must be one of the following constants:

• LUA_OPEQ: compares for equality (==)
• LUA_OPLT: compares for less than (<)
• LUA_OPLE: compares for less or equal (<=)

lua_concat

[-n, +1, e]

void lua_concat (lua_State *L, int n);

Concatenates the n values at the top of the stack, pops them, and leaves the result at the top. If n is 1, the result is the single value on the stack (that is, the function does nothing); if n is 0, the result is the empty string. Concatenation is performed following the usual semantics of Lua (see §3.4.5).

lua_copy

[-0, +0, –]

void lua_copy (lua_State *L, int fromidx, int toidx);

Moves the element at index fromidx into the valid index toidx without shifting any element (therefore replacing the value at that position).

lua_createtable

[-0, +1, e]

void lua_createtable (lua_State *L, int narr, int nrec);

Creates a new empty table and pushes it onto the stack. Parameter narr is a hint for how many elements the table will have as a sequence; parameter nrec is a hint for how many other elements the table will have. Lua may use these hints to preallocate memory for the new table. This pre-allocation is useful for performance when you know in advance how many elements the table will have. Otherwise you can use the function lua_newtable.

lua_dump

[-0, +0, e]

int lua_dump (lua_State *L, lua_Writer writer, void *data);

Dumps a function as a binary chunk. Receives a Lua function on the top of the stack and produces a binary chunk that, if loaded again, results in a function equivalent to the one dumped. As it produces parts of the chunk, lua_dump calls function writer (see lua_Writer) with the given data to write them.

The value returned is the error code returned by the last call to the writer; 0 means no errors.

This function does not pop the Lua function from the stack.

lua_error

[-1, +0, v]

int lua_error (lua_State *L);

Generates a Lua error. The error message (which can actually be a Lua value of any type) must be on the stack top. This function does a long jump, and therefore never returns (see luaL_error).

lua_gc

[-0, +0, e]

int lua_gc (lua_State *L, int what, int data);

Controls the garbage collector.

This function performs several tasks, according to the value of the parameter what:

• LUA_GCSTOP: stops the garbage collector.
• LUA_GCRESTART: restarts the garbage collector.
• LUA_GCCOLLECT: performs a full garbage-collection cycle.
• LUA_GCCOUNT: returns the current amount of memory (in Kbytes) in use by Lua.
• LUA_GCCOUNTB: returns the remainder of dividing the current amount of bytes of memory in use by Lua by 1024.
• LUA_GCSTEP: performs an incremental step of garbage collection. The step “size” is controlled by data (larger values mean more steps) in a non-specified way. If you want to control the step size you must experimentally tune the value of data. The function returns 1 if the step finished a garbage-collection cycle.
• LUA_GCSETPAUSE: sets data as the new value for the pause of the collector (see §2.5). The function returns the previous value of the pause.
• LUA_GCSETSTEPMUL: sets data as the new value for the step multiplier of the collector (see §2.5). The function returns the previous value of the step multiplier.
• LUA_GCISRUNNING: returns a boolean that tells whether the collector is running (i.e., not stopped).
• LUA_GCGEN: changes the collector to generational mode (see §2.5).
• LUA_GCINC: changes the collector to incremental mode. This is the default mode.

For more details about these options, see collectgarbage.

lua_getallocf

[-0, +0, –]

lua_Alloc lua_getallocf (lua_State *L, void **ud);

Returns the memory-allocation function of a given state. If ud is not NULL, Lua stores in *ud the opaque pointer passed to lua_newstate.

lua_getctx

[-0, +0, –]

int lua_getctx (lua_State *L, int *ctx);

This function is called by a continuation function (see §4.7) to retrieve the status of the thread and a context information.

When called in the original function, lua_getctx always returns LUA_OK and does not change the value of its argument ctx. When called inside a continuation function, lua_getctx returns LUA_YIELD and sets the value of ctx to be the context information (the value passed as the ctx argument to the callee together with the continuation function).

When the callee is lua_pcallk, Lua may also call its continuation function to handle errors during the call. That is, upon an error in the function called by lua_pcallk, Lua may not return to the original function but instead may call the continuation function. In that case, a call to lua_getctx will return the error code (the value that would be returned by lua_pcallk); the value of ctx will be set to the context information, as in the case of a yield.

lua_getfield

[-0, +1, e]

void lua_getfield (lua_State *L, int index, const char *k);

Pushes onto the stack the value t[k], where t is the value at the given index. As in Lua, this function may trigger a metamethod for the “index” event (see §2.4).

lua_getglobal

[-0, +1, e]

void lua_getglobal (lua_State *L, const char *name);

Pushes onto the stack the value of the global name.

lua_getmetatable

[-0, +(0|1), –]

int lua_getmetatable (lua_State *L, int index);

Pushes onto the stack the metatable of the value at the given index. If the value does not have a metatable, the function returns 0 and pushes nothing on the stack.

lua_gettable

[-1, +1, e]

void lua_gettable (lua_State *L, int index);

Pushes onto the stack the value t[k], where t is the value at the given index and k is the value at the top of the stack.

This function pops the key from the stack (putting the resulting value in its place). As in Lua, this function may trigger a metamethod for the “index” event (see §2.4).

lua_gettop

[-0, +0, –]

int lua_gettop (lua_State *L);

Returns the index of the top element in the stack. Because indices start at 1, this result is equal to the number of elements in the stack (and so 0 means an empty stack).

lua_getuservalue

[-0, +1, –]

void lua_getuservalue (lua_State *L, int index);

Pushes onto the stack the Lua value associated with the userdata at the given index. This Lua value must be a table or nil.

lua_insert

[-1, +1, –]

void lua_insert (lua_State *L, int index);

Moves the top element into the given valid index, shifting up the elements above this index to open space. This function cannot be called with a pseudo-index, because a pseudo-index is not an actual stack position.

lua_Integer

typedef ptrdiff_t lua_Integer;

The type used by the Lua API to represent signed integral values.

By default it is a ptrdiff_t, which is usually the largest signed integral type the machine handles “comfortably”.

lua_isboolean

[-0, +0, –]

int lua_isboolean (lua_State *L, int index);

Returns 1 if the value at the given index is a boolean, and 0 otherwise.

lua_iscfunction

[-0, +0, –]

int lua_iscfunction (lua_State *L, int index);

Returns 1 if the value at the given index is a C function, and 0 otherwise.

lua_isfunction

[-0, +0, –]

int lua_isfunction (lua_State *L, int index);

Returns 1 if the value at the given index is a function (either C or Lua), and 0 otherwise.

lua_islightuserdata

[-0, +0, –]

int lua_islightuserdata (lua_State *L, int index);

Returns 1 if the value at the given index is a light userdata, and 0 otherwise.

lua_isnil

[-0, +0, –]

int lua_isnil (lua_State *L, int index);

Returns 1 if the value at the given index is nil, and 0 otherwise.

lua_isnone

[-0, +0, –]

int lua_isnone (lua_State *L, int index);

Returns 1 if the given index is not valid, and 0 otherwise.

lua_isnoneornil

[-0, +0, –]

int lua_isnoneornil (lua_State *L, int index);

Returns 1 if the given index is not valid or if the value at this index is nil, and 0 otherwise.

lua_isnumber

[-0, +0, –]

int lua_isnumber (lua_State *L, int index);

Returns 1 if the value at the given index is a number or a string convertible to a number, and 0 otherwise.

lua_isstring

[-0, +0, –]

int lua_isstring (lua_State *L, int index);

Returns 1 if the value at the given index is a string or a number (which is always convertible to a string), and 0 otherwise.

lua_istable

[-0, +0, –]

int lua_istable (lua_State *L, int index);

Returns 1 if the value at the given index is a table, and 0 otherwise.

lua_isthread

[-0, +0, –]

int lua_isthread (lua_State *L, int index);

Returns 1 if the value at the given index is a thread, and 0 otherwise.

lua_isuserdata

[-0, +0, –]

int lua_isuserdata (lua_State *L, int index);

Returns 1 if the value at the given index is a userdata (either full or light), and 0 otherwise.

lua_len

[-0, +1, e]

void lua_len (lua_State *L, int index);

Returns the “length” of the value at the given index; it is equivalent to the ‘#‘ operator in Lua (see §3.4.6). The result is pushed on the stack.

lua_load

[-0, +1, –]

int lua_load (lua_State *L,
              lua_Reader reader,
              void *data,
              const char *source,
              const char *mode);

Loads a Lua chunk (without running it). If there are no errors, lua_load pushes the compiled chunk as a Lua function on top of the stack. Otherwise, it pushes an error message.

The return values of lua_load are:

• LUA_OK: no errors;
• LUA_ERRSYNTAX: syntax error during precompilation;
• LUA_ERRMEM: memory allocation error;
• LUA_ERRGCMM: error while running a __gc metamethod. (This error has no relation with the chunk being loaded. It is generated by the garbage collector.)

The lua_load function uses a user-supplied reader function to read the chunk (see lua_Reader). The data argument is an opaque value passed to the reader function.

The source argument gives a name to the chunk, which is used for error messages and in debug information (see §4.9).

lua_load automatically detects whether the chunk is text or binary and loads it accordingly (see program luac). The string mode works as in function load, with the addition that a NULL value is equivalent to the string “bt“.

lua_load uses the stack internally, so the reader function should always leave the stack unmodified when returning.

If the resulting function has one upvalue, this upvalue is set to the value of the global environment stored at index LUA_RIDX_GLOBALS in the registry (see §4.5). When loading main chunks, this upvalue will be the _ENV variable (see §2.2).

lua_newstate

[-0, +0, –]

lua_State *lua_newstate (lua_Alloc f, void *ud);

Creates a new thread running in a new, independent state. Returns NULL if cannot create the thread or the state (due to lack of memory). The argument f is the allocator function; Lua does all memory allocation for this state through this function. The second argument, ud, is an opaque pointer that Lua passes to the allocator in every call.

lua_newtable

[-0, +1, e]

void lua_newtable (lua_State *L);

Creates a new empty table and pushes it onto the stack. It is equivalent to lua_createtable(L, 0, 0).

lua_newthread

[-0, +1, e]

lua_State *lua_newthread (lua_State *L);

Creates a new thread, pushes it on the stack, and returns a pointer to a lua_State that represents this new thread. The new thread returned by this function shares with the original thread its global environment, but has an independent execution stack.

There is no explicit function to close or to destroy a thread. Threads are subject to garbage collection, like any Lua object.

lua_newuserdata

[-0, +1, e]

void *lua_newuserdata (lua_State *L, size_t size);

This function allocates a new block of memory with the given size, pushes onto the stack a new full userdata with the block address, and returns this address. The host program can freely use this memory.

lua_next

[-1, +(2|0), e]

int lua_next (lua_State *L, int index);

Pops a key from the stack, and pushes a key–value pair from the table at the given index (the “next” pair after the given key). If there are no more elements in the table, then lua_next returns 0 (and pushes nothing).

A typical traversal looks like this:

     /* table is in the stack at index 't' */
     lua_pushnil(L);  /* first key */
     while (lua_next(L, t) != 0) {
       /* uses 'key' (at index -2) and 'value' (at index -1) */
       printf("%s - %s\n",
              lua_typename(L, lua_type(L, -2)),
              lua_typename(L, lua_type(L, -1)));
       /* removes 'value'; keeps 'key' for next iteration */
       lua_pop(L, 1);
     }

While traversing a table, do not call lua_tolstring directly on a key, unless you know that the key is actually a string. Recall that lua_tolstring may change the value at the given index; this confuses the next call to lua_next.

See function next for the caveats of modifying the table during its traversal.

lua_Number

typedef double lua_Number;

The type of numbers in Lua. By default, it is double, but that can be changed in luaconf.h. Through this configuration file you can change Lua to operate with another type for numbers (e.g., float or long).

lua_pcall

[-(nargs + 1), +(nresults|1), –]

int lua_pcall (lua_State *L, int nargs, int nresults, int msgh);

Calls a function in protected mode.

Both nargs and nresults have the same meaning as in lua_call. If there are no errors during the call, lua_pcall behaves exactly like lua_call. However, if there is any error, lua_pcall catches it, pushes a single value on the stack (the error message), and returns an error code. Like lua_call, lua_pcall always removes the function and its arguments from the stack.

If msgh is 0, then the error message returned on the stack is exactly the original error message. Otherwise, msgh is the stack index of a message handler. (In the current implementation, this index cannot be a pseudo-index.) In case of runtime errors, this function will be called with the error message and its return value will be the message returned on the stack by lua_pcall.

Typically, the message handler is used to add more debug information to the error message, such as a stack traceback. Such information cannot be gathered after the return of lua_pcall, since by then the stack has unwound.

The lua_pcall function returns one of the following codes (defined in lua.h):

• LUA_OK (0): success.
• LUA_ERRRUN: a runtime error.
• LUA_ERRMEM: memory allocation error. For such errors, Lua does not call the message handler.
• LUA_ERRERR: error while running the message handler.
• LUA_ERRGCMM: error while running a __gc metamethod. (This error typically has no relation with the function being called. It is generated by the garbage collector.)

lua_pcallk

[-(nargs + 1), +(nresults|1), –]

int lua_pcallk (lua_State *L,
                int nargs,
                int nresults,
                int errfunc,
                int ctx,
                lua_CFunction k);

This function behaves exactly like lua_pcall, but allows the called function to yield (see §4.7).

lua_pop

[-n, +0, –]

void lua_pop (lua_State *L, int n);

Pops n elements from the stack.

lua_pushboolean

[-0, +1, –]

void lua_pushboolean (lua_State *L, int b);

Pushes a boolean value with value b onto the stack.

lua_pushcclosure

[-n, +1, e]

void lua_pushcclosure (lua_State *L, lua_CFunction fn, int n);

Pushes a new C closure onto the stack.

When a C function is created, it is possible to associate some values with it, thus creating a C closure (see §4.4); these values are then accessible to the function whenever it is called. To associate values with a C function, first these values should be pushed onto the stack (when there are multiple values, the first value is pushed first). Then lua_pushcclosure is called to create and push the C function onto the stack, with the argument n telling how many values should be associated with the function. lua_pushcclosure also pops these values from the stack.

The maximum value for n is 255.

When n is zero, this function creates a light C function, which is just a pointer to the C function. In that case, it never throws a memory error.

lua_pushcfunction

[-0, +1, –]

void lua_pushcfunction (lua_State *L, lua_CFunction f);

Pushes a C function onto the stack. This function receives a pointer to a C function and pushes onto the stack a Lua value of type function that, when called, invokes the corresponding C function.

Any function to be registered in Lua must follow the correct protocol to receive its parameters and return its results (see lua_CFunction).

lua_pushcfunction is defined as a macro:

     #define lua_pushcfunction(L,f)  lua_pushcclosure(L,f,0)

Note that f is used twice.

lua_pushfstring

[-0, +1, e]

const char *lua_pushfstring (lua_State *L, const char *fmt, ...);

Pushes onto the stack a formatted string and returns a pointer to this string. It is similar to the ISO C function sprintf, but has some important differences:

• You do not have to allocate space for the result: the result is a Lua string and Lua takes care of memory allocation (and deallocation, through garbage collection).
• The conversion specifiers are quite restricted. There are no flags, widths, or precisions. The conversion specifiers can only be ‘%%‘ (inserts a ‘%‘ in the string), ‘%s‘ (inserts a zero-terminated string, with no size restrictions), ‘%f‘ (inserts a lua_Number), ‘%p‘ (inserts a pointer as a hexadecimal numeral), ‘%d‘ (inserts an int), and ‘%c‘ (inserts an int as a byte).

lua_pushglobaltable

[-0, +1, –]

void lua_pushglobaltable (lua_State *L);

Pushes the global environment onto the stack.

lua_pushinteger

[-0, +1, –]

void lua_pushinteger (lua_State *L, lua_Integer n);

Pushes a number with value n onto the stack.

lua_pushlightuserdata

[-0, +1, –]

void lua_pushlightuserdata (lua_State *L, void *p);

Pushes a light userdata onto the stack.

Userdata represent C values in Lua. A light userdata represents a pointer, a void*. It is a value (like a number): you do not create it, it has no individual metatable, and it is not collected (as it was never created). A light userdata is equal to “any” light userdata with the same C address.

lua_pushliteral

[-0, +1, e]

const char *lua_pushliteral (lua_State *L, const char *s);

This macro is equivalent to lua_pushlstring, but can be used only when s is a literal string. It automatically provides the string length.

lua_pushlstring

[-0, +1, e]

const char *lua_pushlstring (lua_State *L, const char *s, size_t len);

Pushes the string pointed to by s with size len onto the stack. Lua makes (or reuses) an internal copy of the given string, so the memory at s can be freed or reused immediately after the function returns. The string can contain any binary data, including embedded zeros.

Returns a pointer to the internal copy of the string.

lua_pushnil

[-0, +1, –]

void lua_pushnil (lua_State *L);

Pushes a nil value onto the stack.

lua_pushnumber

[-0, +1, –]

void lua_pushnumber (lua_State *L, lua_Number n);

Pushes a number with value n onto the stack.

lua_pushstring

[-0, +1, e]

const char *lua_pushstring (lua_State *L, const char *s);

Pushes the zero-terminated string pointed to by s onto the stack. Lua makes (or reuses) an internal copy of the given string, so the memory at s can be freed or reused immediately after the function returns.

Returns a pointer to the internal copy of the string.

If s is NULL, pushes nil and returns NULL.

lua_pushthread

[-0, +1, –]

int lua_pushthread (lua_State *L);

Pushes the thread represented by L onto the stack. Returns 1 if this thread is the main thread of its state.

lua_pushunsigned

[-0, +1, –]

void lua_pushunsigned (lua_State *L, lua_Unsigned n);

Pushes a number with value n onto the stack.

lua_pushvalue

[-0, +1, –]

void lua_pushvalue (lua_State *L, int index);

Pushes a copy of the element at the given index onto the stack.

lua_pushvfstring

[-0, +1, e]

const char *lua_pushvfstring (lua_State *L,
                              const char *fmt,
                              va_list argp);

Equivalent to lua_pushfstring, except that it receives a va_list instead of a variable number of arguments.

lua_rawequal

[-0, +0, –]

int lua_rawequal (lua_State *L, int index1, int index2);

Returns 1 if the two values in indices index1 and index2 are primitively equal (that is, without calling metamethods). Otherwise returns 0. Also returns 0 if any of the indices are non valid.

lua_rawget

[-1, +1, –]

void lua_rawget (lua_State *L, int index);

Similar to lua_gettable, but does a raw access (i.e., without metamethods).

lua_rawgeti

[-0, +1, –]

void lua_rawgeti (lua_State *L, int index, int n);

Pushes onto the stack the value t[n], where t is the table at the given index. The access is raw; that is, it does not invoke metamethods.

lua_rawgetp

[-0, +1, –]

void lua_rawgetp (lua_State *L, int index, const void *p);

Pushes onto the stack the value t[k], where t is the table at the given index and k is the pointer p represented as a light userdata. The access is raw; that is, it does not invoke metamethods.

lua_rawlen

[-0, +0, –]

size_t lua_rawlen (lua_State *L, int index);

Returns the raw “length” of the value at the given index: for strings, this is the string length; for tables, this is the result of the length operator (‘#‘) with no metamethods; for userdata, this is the size of the block of memory allocated for the userdata; for other values, it is 0.

lua_rawset

[-2, +0, e]

void lua_rawset (lua_State *L, int index);

Similar to lua_settable, but does a raw assignment (i.e., without metamethods).

lua_rawseti

[-1, +0, e]

void lua_rawseti (lua_State *L, int index, int n);

Does the equivalent of t[n] = v, where t is the table at the given index and v is the value at the top of the stack.

This function pops the value from the stack. The assignment is raw; that is, it does not invoke metamethods.

lua_rawsetp

[-1, +0, e]

void lua_rawsetp (lua_State *L, int index, const void *p);

Does the equivalent of t[k] = v, where t is the table at the given index, k is the pointer p represented as a light userdata, and v is the value at the top of the stack.

This function pops the value from the stack. The assignment is raw; that is, it does not invoke metamethods.

lua_Reader

typedef const char * (*lua_Reader) (lua_State *L,
                                    void *data,
                                    size_t *size);

The reader function used by lua_load. Every time it needs another piece of the chunk, lua_load calls the reader, passing along its data parameter. The reader must return a pointer to a block of memory with a new piece of the chunk and set size to the block size. The block must exist until the reader function is called again. To signal the end of the chunk, the reader must return NULL or set size to zero. The reader function may return pieces of any size greater than zero.

lua_register

[-0, +0, e]

void lua_register (lua_State *L, const char *name, lua_CFunction f);

Sets the C function f as the new value of global name. It is defined as a macro:

     #define lua_register(L,n,f) \
            (lua_pushcfunction(L, f), lua_setglobal(L, n))

lua_remove

[-1, +0, –]

void lua_remove (lua_State *L, int index);

Removes the element at the given valid index, shifting down the elements above this index to fill the gap. This function cannot be called with a pseudo-index, because a pseudo-index is not an actual stack position.

lua_replace

[-1, +0, –]

void lua_replace (lua_State *L, int index);

Moves the top element into the given valid index without shifting any element (therefore replacing the value at the given index), and then pops the top element.

lua_resume

[-?, +?, –]

int lua_resume (lua_State *L, lua_State *from, int nargs);

Starts and resumes a coroutine in a given thread.

To start a coroutine, you push onto the thread stack the main function plus any arguments; then you call lua_resume, with nargs being the number of arguments. This call returns when the coroutine suspends or finishes its execution. When it returns, the stack contains all values passed to lua_yield, or all values returned by the body function. lua_resume returns LUA_YIELD if the coroutine yields, LUA_OK if the coroutine finishes its execution without errors, or an error code in case of errors (see lua_pcall).

In case of errors, the stack is not unwound, so you can use the debug API over it. The error message is on the top of the stack.

To resume a coroutine, you remove any results from the last lua_yield, put on its stack only the values to be passed as results from yield, and then call lua_resume.

The parameter from represents the coroutine that is resuming L. If there is no such coroutine, this parameter can be NULL.

lua_setallocf

[-0, +0, –]

void lua_setallocf (lua_State *L, lua_Alloc f, void *ud);

Changes the allocator function of a given state to f with user data ud.

lua_setfield

[-1, +0, e]

void lua_setfield (lua_State *L, int index, const char *k);

Does the equivalent to t[k] = v, where t is the value at the given index and v is the value at the top of the stack.

This function pops the value from the stack. As in Lua, this function may trigger a metamethod for the “newindex” event (see §2.4).

lua_setglobal

[-1, +0, e]

void lua_setglobal (lua_State *L, const char *name);

Pops a value from the stack and sets it as the new value of global name.

lua_setmetatable

[-1, +0, –]

void lua_setmetatable (lua_State *L, int index);

Pops a table from the stack and sets it as the new metatable for the value at the given index.

lua_settable

[-2, +0, e]

void lua_settable (lua_State *L, int index);

Does the equivalent to t[k] = v, where t is the value at the given index, v is the value at the top of the stack, and k is the value just below the top.

This function pops both the key and the value from the stack. As in Lua, this function may trigger a metamethod for the “newindex” event (see §2.4).

lua_settop

[-?, +?, –]

void lua_settop (lua_State *L, int index);

Accepts any index, or 0, and sets the stack top to this index. If the new top is larger than the old one, then the new elements are filled with nil. If index is 0, then all stack elements are removed.

lua_setuservalue

[-1, +0, –]

void lua_setuservalue (lua_State *L, int index);

Pops a table or nil from the stack and sets it as the new value associated to the userdata at the given index.

lua_State

typedef struct lua_State lua_State;

An opaque structure that points to a thread and indirectly (through the thread) to the whole state of a Lua interpreter. The Lua library is fully reentrant: it has no global variables. All information about a state is accessible through this structure.

A pointer to this structure must be passed as the first argument to every function in the library, except to lua_newstate, which creates a Lua state from scratch.

lua_status

[-0, +0, –]

int lua_status (lua_State *L);

Returns the status of the thread L.

The status can be 0 (LUA_OK) for a normal thread, an error code if the thread finished the execution of a lua_resume with an error, or LUA_YIELD if the thread is suspended.

You can only call functions in threads with status LUA_OK. You can resume threads with status LUA_OK (to start a new coroutine) or LUA_YIELD (to resume a coroutine).

lua_toboolean

[-0, +0, –]

int lua_toboolean (lua_State *L, int index);

Converts the Lua value at the given index to a C boolean value (0 or 1). Like all tests in Lua, lua_toboolean returns true for any Lua value different from false and nil; otherwise it returns false. (If you want to accept only actual boolean values, use lua_isboolean to test the value’s type.)

lua_tocfunction

[-0, +0, –]

lua_CFunction lua_tocfunction (lua_State *L, int index);

Converts a value at the given index to a C function. That value must be a C function; otherwise, returns NULL.

lua_tointeger

[-0, +0, –]

lua_Integer lua_tointeger (lua_State *L, int index);

Equivalent to lua_tointegerx with isnum equal to NULL.

lua_tointegerx

[-0, +0, –]

lua_Integer lua_tointegerx (lua_State *L, int index, int *isnum);

Converts the Lua value at the given index to the signed integral type lua_Integer. The Lua value must be a number or a string convertible to a number (see §3.4.2); otherwise, lua_tointegerx returns 0.

If the number is not an integer, it is truncated in some non-specified way.

If isnum is not NULL, its referent is assigned a boolean value that indicates whether the operation succeeded.

lua_tolstring

[-0, +0, e]

const char *lua_tolstring (lua_State *L, int index, size_t *len);

Converts the Lua value at the given index to a C string. If len is not NULL, it also sets *len with the string length. The Lua value must be a string or a number; otherwise, the function returns NULL. If the value is a number, then lua_tolstring also changes the actual value in the stack to a string. (This change confuses lua_next when lua_tolstring is applied to keys during a table traversal.)

lua_tolstring returns a fully aligned pointer to a string inside the Lua state. This string always has a zero (‘\0‘) after its last character (as in C), but can contain other zeros in its body. Because Lua has garbage collection, there is no guarantee that the pointer returned by lua_tolstring will be valid after the corresponding value is removed from the stack.

lua_tonumber

[-0, +0, –]

lua_Number lua_tonumber (lua_State *L, int index);

Equivalent to lua_tonumberx with isnum equal to NULL.

lua_tonumberx

[-0, +0, –]

lua_Number lua_tonumberx (lua_State *L, int index, int *isnum);

Converts the Lua value at the given index to the C type lua_Number (see lua_Number). The Lua value must be a number or a string convertible to a number (see §3.4.2); otherwise, lua_tonumberx returns 0.

If isnum is not NULL, its referent is assigned a boolean value that indicates whether the operation succeeded.

lua_topointer

[-0, +0, –]

const void *lua_topointer (lua_State *L, int index);

Converts the value at the given index to a generic C pointer (void*). The value can be a userdata, a table, a thread, or a function; otherwise, lua_topointer returns NULL. Different objects will give different pointers. There is no way to convert the pointer back to its original value.

Typically this function is used only for debug information.

lua_tostring

[-0, +0, e]

const char *lua_tostring (lua_State *L, int index);

Equivalent to lua_tolstring with len equal to NULL.

lua_tothread

[-0, +0, –]

lua_State *lua_tothread (lua_State *L, int index);

Converts the value at the given index to a Lua thread (represented as lua_State*). This value must be a thread; otherwise, the function returns NULL.

lua_tounsigned

[-0, +0, –]

lua_Unsigned lua_tounsigned (lua_State *L, int index);

Equivalent to lua_tounsignedx with isnum equal to NULL.

lua_tounsignedx

[-0, +0, –]

lua_Unsigned lua_tounsignedx (lua_State *L, int index, int *isnum);

Converts the Lua value at the given index to the unsigned integral type lua_Unsigned. The Lua value must be a number or a string convertible to a number (see §3.4.2); otherwise, lua_tounsignedx returns 0.

If the number is not an integer, it is truncated in some non-specified way. If the number is outside the range of representable values, it is normalized to the remainder of its division by one more than the maximum representable value.

If isnum is not NULL, its referent is assigned a boolean value that indicates whether the operation succeeded.

lua_touserdata

[-0, +0, –]

void *lua_touserdata (lua_State *L, int index);

If the value at the given index is a full userdata, returns its block address. If the value is a light userdata, returns its pointer. Otherwise, returns NULL.

lua_type

[-0, +0, –]

int lua_type (lua_State *L, int index);

Returns the type of the value in the given valid index, or LUA_TNONE for a non-valid (but acceptable) index. The types returned by lua_type are coded by the following constants defined in lua.h: LUA_TNIL, LUA_TNUMBER, LUA_TBOOLEAN, LUA_TSTRING, LUA_TTABLE, LUA_TFUNCTION, LUA_TUSERDATA, LUA_TTHREAD, and LUA_TLIGHTUSERDATA.

lua_typename

[-0, +0, –]

const char *lua_typename (lua_State *L, int tp);

Returns the name of the type encoded by the value tp, which must be one the values returned by lua_type.

lua_Unsigned

typedef unsigned long lua_Unsigned;

The type used by the Lua API to represent unsigned integral values. It must have at least 32 bits.

By default it is an unsigned int or an unsigned long, whichever can hold 32-bit values.

lua_upvalueindex

[-0, +0, –]

int lua_upvalueindex (int i);

Returns the pseudo-index that represents the i-th upvalue of the running function (see §4.4).

lua_version

[-0, +0, v]

const lua_Number *lua_version (lua_State *L);

Returns the address of the version number stored in the Lua core. When called with a valid lua_State, returns the address of the version used to create that state. When called with NULL, returns the address of the version running the call.

lua_Writer

typedef int (*lua_Writer) (lua_State *L,
                           const void* p,
                           size_t sz,
                           void* ud);

The type of the writer function used by lua_dump. Every time it produces another piece of chunk, lua_dump calls the writer, passing along the buffer to be written (p), its size (sz), and the data parameter supplied to lua_dump.

The writer returns an error code: 0 means no errors; any other value means an error and stops lua_dump from calling the writer again.

lua_xmove

[-?, +?, –]

void lua_xmove (lua_State *from, lua_State *to, int n);

Exchange values between different threads of the same state.

This function pops n values from the stack from, and pushes them onto the stack to.

lua_yield

[-?, +?, –]

int lua_yield (lua_State *L, int nresults);

This function is equivalent to lua_yieldk, but it has no continuation (see §4.7). Therefore, when the thread resumes, it returns to the function that called the function calling lua_yield.

lua_yieldk

[-?, +?, –]

int lua_yieldk (lua_State *L, int nresults, int ctx, lua_CFunction k);

Yields a coroutine.

This function should only be called as the return expression of a C function, as follows:

     return lua_yieldk (L, n, i, k);

When a C function calls lua_yieldk in that way, the running coroutine suspends its execution, and the call to lua_resume that started this coroutine returns. The parameter nresults is the number of values from the stack that are passed as results to lua_resume.

When the coroutine is resumed again, Lua calls the given continuation function k to continue the execution of the C function that yielded (see §4.7). This continuation function receives the same stack from the previous function, with the results removed and replaced by the arguments passed to lua_resume. Moreover, the continuation function may access the value ctx by calling lua_getctx.