As well as other features and bugfixes.
tolua is a tool that greatly simplifies the integration of C/C++ code with Lua. Based on a cleaned header file (or extracts from real header files), tolua automatically generates the binding code to access C/C++ features from Lua. Using Lua API and tag method facilities, tolua maps C/C++ constants, external variables, functions, classes, and methods to Lua.
This manual is for tolua++ version 1.0 and is implemented upon Lua 5.0 and based on tolua 5.0. See Compatibility for details on switching from older versions.
The sections below describe how to use tolua. Please contact us with bug reports, suggestions, and comments.
Let's start with some examples. If we specify as input the following C-like header file to tolua:
#define FALSE 0 #define TRUE 1 enum { POINT = 100, LINE, POLYGON }
Object* createObejct (int type); void drawObject (Object* obj, double red, double green, double blue); int isSelected (Object* obj);A C file that binds such a code to Lua is automatically generated. Therefore, in Lua code, we can access the C code, writing, for instance:
... myLine = createObject(LINE) ... if isSelected(myLine) == TRUE then drawObject(myLine, 1.0, 0.0, 0.0); else drawObject(myLine, 1.0, 1.0, 1.0); end ...Also, consider a C++-like header file:
#define FALSE 0 #define TRUE 1
class Shape { void draw (void); void draw (double red, double green, double blue); int isSelected (void); };
class Line : public Shape { Line (double x1, double y1, double x2, double y2); ~Line (void); };If this file is used as input to tolua, a C++ file is automatically generated proving access to such a code from Lua. Therefore, it would be valid to write Lua statements like:
... myLine = Line:new (0,0,1,1) ... if myLine:isSelected() == TRUE then myLine:draw(1.0,0.0,0.0) else myLine:draw() end ... myLine:delete() ...The package file (usually with extension .pkg) passed to tolua is not the real C/C++ header file, but a cleaned version of it. tolua does not implement a complete parse to interpret C/C++ code, but it understands a few declarations that are used to describe the features that are to be exported to Lua. Regular header files can be included into packages files; tolua will extract the code specified by the user to parse from the header (see Basic Concepts).
tolua -o myfile.c myfile.pkg
The generated code must be compiled and linked with the application to provide the desired access from Lua. Each parsed file represents a package being exported to Lua. By default, the package name is the input file root name (myfile in the example). The user can specify a different name for the package:
tolua -n pkgname -o myfile.c myfile.pkg
The package should also be explicitly initialized. To initialize the package from our C/C++ code, we must declare and call the initialization function. The initialization function is defined as
int tolua_pkgname_open (lua_State*);
where pkgname represents the name of the package being bound. If we are using C++, we can opt for automatic initialization:
tolua -a -n pkgname -o myfile.c myfile.pkg
In that case, the initialization function is automatically called. However, if we are planning to use multiple Lua states, automatic initialization does not work, because the order static variables are initialized in C++ is not defined.
Optionally, the prototype of the open function can be outputted to a header file, which name is given by the -H option.
The binding code generated by tolua uses a set of functions defined in the tolua library. Thus, this library also has to be linked with the application. The file tolua.h is also necessary to compile the generated code.
An application can use tolua object oriented framework (see exported utility functions) without binding any package. In that case, the application must call tolua initialization function (this function is called by any package file initialization function):
int tolua_open (void);
$pfile "include_file"
A package file may also include regular C/C++ header files, using the hfile or cfile directive:
$cfile "example.h"
In which case, tolua will extract the code enclosed between tolua_begin and tolua_end, or or tolua_export for a single line. Consider this C++ header as example:
#ifndef EXAMPLE_H #define EXAMPLE_H class Example { // tolua_export private: string name; int number; public: void set_number(int number); //tolua_begin string get_name(); int get_number(); }; // tolua_end #endif
In this case, the code that's not supported by tolua (the private part of the class), along with the function set_number is left outside of the package that includes this header.
Finally, lua files can be included on a package file, using $lfile:
$lfile "example.lua"
New on tolua++: an extra way to include source files is available since version 1.0.4 of tolua++, using ifile:
$ifile "filename"
ifile also takes extra optional parameters after the filename, for example:
$ifile "widget.h", GUI
$ifile "vector.h", math, 3d
ifile's default behaviour is to include the whole file, untouched. However, the contents of the file and the extra parameters are put through the include_file_hook function before being included into the package (see Customizing tolua++ for more details).
Functions in C/C++ can also manipulate Lua objects explicitly. Thus lua_Object is also considered a basic type. In this case, any Lua value matches it.
New on tolua++: The C++ type string is also considered a basic type, and is passed as a value to lua (using the c_str() method). This feature can be turned off with the command line option -S.
For user defined types, constness is preserved. Thus passing a non constant user defined type to a function that expects constant type generates an type mismatching error.
typedef double real;
Otherwise, real would be interpreted as a user defined type and would not be mapped to Lua numbers.
/* specify the files to be included */
$#include "header1.h" // include first header $#include "header2.h" // include second headerAs illustrated, tolua also accepts comments, using C or C++ convention, inside the package file. Nested C-like comments can also be used.
Also note that files included with $cfile or $hfile don't need to be included using this method, this is done automatically by tolua.
In the following sections, we describe how to specify the C/C++ code we want to bind to Lua. The formats are simplified valid C/C++ statements.
#define NAME [ VALUE ]The value, as showed above, is optional. If such a code is inserted inside the file being processed, tolua generates a code that allows the use of NAME as a Lua global variable that has the corresponding C/C++ constant value. Only numeric constants are accepted.
New on tolua++: All other preprocessor directives are ignored.
For enum's, the general format is:
enum { NAME1 [ = VALUE1 ] , NAME2 [ = VALUE2 ] , ... NAMEn [ = VALUEn ] };Similarly, tolua creates a set of global variables, named NAMEi, with their corresponding values.
[extern] type var;tolua binds such declarations to Lua global variables. Thus, in Lua, we can access the C/C++ variable naturally. If the variable is non constant, we can also assign the variable a new value from Lua. Global variables that represent arrays of value can also be bound to Lua. Arrays can be of any type. The corresponding Lua objects for arrays are Lua tables indexed with numeric values; however, be aware that index 1 in Lua is mapped to index 0 in an C/C++ array. Arrays must be pre dimensioned. For instance:
double v[10];
New on tolua++: External variables can use the tolua_readonly modifier (see Additional Features)
type funcname (type1 par1[, type2 par2[,...typeN parN]]);The returned type can be void, meaning no value is returned. A function can also have no parameter. In that case, void may be specified in the place of the list of parameters. The parameter types must follow the rules already posted. tolua creates a Lua function binding the C/C++ function. When calling a function from Lua, the parameter types must match the corresponding C/C++ types, otherwise, tolua generates an error and reports which parameter is wrongly specified. If a parameter name is omitted, tolua names it automatically, but its type should be a basic type or user type previously used.
The arrays must be pre dimensioned. For instance:
void func (double a[3]);
is a valid function declaration for tolua and calling this function from Lua would be done by, for instance:
p = {1.0,1.5,8.6}
func (p)
The array dimension need not be a constant expression; the dimension can also be specified by any expression that can be evaluated in run time. For instance:
void func (int n, int m, double image[n*m]);
is also valid since the expression n*m is valid in the binding function scope. However, be aware that tolua uses dynamic allocation for binding this function, what can degrade the performance.
Despite the dimension specification, it is important to know that all arrays passed to the actual C/C++ function are in the local scope of the binding function. So, if the C/C++ function being called needs to hold the array pointer for later use, the binding code will not work properly.
void func (int a);
void func (double a);
represent two different functions in C++, they are the same function for tolua, because both int and double are mapped to the same Lua type: number.
Another tricky situation occurs when expecting pointers. Suppose:
void func (char* s); void func (void* p); void func (Object1* ptr); void func (Object2* prt);Although these four functions represent different functions in C++, a Lua statement like:
func(nil)matches all of them.
It is important to know that tolua decides which function will be called in run-time, trying to match each provided function. tolua first tries to call the last specified function; if it fails, tolua then tries the previous one. This process is repeated until one function matches the calling code or the first function is reached. For that reason, the mismatching error message, when it occurs, is based on the first function specification. When performance is important, we can specify the most used function as the last one, because it will be tried first.
tolua allows the use of overloaded functions in C, see Renaming for details.