This chapter discusses SWIG's support of Tcl. SWIG currently requires Tcl 8.0 or a later release. Earlier releases of SWIG supported Tcl 7.x, but this is no longer supported.
If building a C++ extension, add the -c++ option:$ swig -tcl example.i
$ swig -c++ -tcl example.i
This creates a file example_wrap.c or example_wrap.cxx that contains all of the code needed to build a Tcl extension module. To finish building the module, you need to compile this file and link it with the rest of your program.
Be aware that some Tcl versions install this header file with a version number attached to it. If this is the case, you should probably make a symbolic link so that tcl.h points to the correct header file./usr/local/include
The exact commands for doing this vary from platform to platform. SWIG tries to guess the right options when it is installed. Therefore, you may want to start with one of the examples in the SWIG/Examples/tcl directory. If that doesn't work, you will need to read the man-pages for your compiler and linker to get the right set of options. You might also check the SWIG Wiki for additional information.$ swig -tcl example.i $ gcc -c example.c $ gcc -c example_wrap.c -I/usr/local/include $ gcc -shared example.o example_wrap.o -o example.so
When linking the module, the name of the output file has to match the name of the module. If the name of your SWIG module is "example", the name of the corresponding object file should be "example.so". The name of the module is specified using the %module directive or the -module command line option.
The usual procedure for adding a new module to Tcl involves writing a special function Tcl_AppInit() and using it to initialize the interpreter and your module. With SWIG, the tclsh.i and wish.i library files can be used to rebuild the tclsh and wish interpreters respectively. For example:
The tclsh.i library file includes supporting code that contains everything needed to rebuild tclsh. To rebuild the interpreter, you simply do something like this:%module example extern int fact(int); extern int mod(int, int); extern double My_variable; %include tclsh.i // Include code for rebuilding tclsh
You will need to supply the same libraries that were used to build Tcl the first time. This may include system libraries such as -lsocket, -lnsl, and -lpthread. If this actually works, the new version of Tcl should be identical to the default version except that your extension module will be a built-in part of the interpreter.$ swig -tcl example.i $ gcc example.c example_wrap.c \ -Xlinker -export-dynamic \ -DHAVE_CONFIG_H -I/usr/local/include/ \ -L/usr/local/lib -ltcl -lm -ldl \ -o mytclsh
Comment: In practice, you should probably try to avoid static linking if possible. Some programmers may be inclined to use static linking in the interest of getting better performance. However, the performance gained by static linking tends to be rather minimal in most situations (and quite frankly not worth the extra hassle in the opinion of this author).
A common error received by first-time users is the following:$ tclsh % load ./example.so % fact 4 24 %
This error is almost always caused when the name of the shared object file doesn't match the name of the module supplied using the SWIG %module directive. Double-check the interface to make sure the module name and the shared object file match. Another possible cause of this error is forgetting to link the SWIG-generated wrapper code with the rest of your application when creating the extension module.% load ./example.so couldn't find procedure Example_Init %
Another common error is something similar to the following:
This error usually indicates that you forgot to include some object files or libraries in the linking of the shared library file. Make sure you compile both the SWIG wrapper file and your original program into a shared library file. Make sure you pass all of the required libraries to the linker.% load ./example.so couldn't load file "./example.so": ./example.so: undefined symbol: fact %
Sometimes unresolved symbols occur because a wrapper has been created for a function that doesn't actually exist in a library. This usually occurs when a header file includes a declaration for a function that was never actually implemented or it was removed from a library without updating the header file. To fix this, you can either edit the SWIG input file to remove the offending declaration or you can use the %ignore directive to ignore the declaration.
Finally, suppose that your extension module is linked with another library like this:
If the foo library is compiled as a shared library, you might get the following problem when you try to use your module:$ gcc -shared example.o example_wrap.o -L/home/beazley/projects/lib -lfoo \ -o example.so
This error is generated because the dynamic linker can't locate the libfoo.so library. When shared libraries are loaded, the system normally only checks a few standard locations such as /usr/lib and /usr/local/lib. To fix this problem, there are several things you can do. First, you can recompile your extension module with extra path information. For example, on Linux you can do this:% load ./example.so couldn't load file "./example.so": libfoo.so: cannot open shared object file: No such file or directory %
Alternatively, you can set the LD_LIBRARY_PATH environment variable to include the directory with your shared libraries. If setting LD_LIBRARY_PATH, be aware that setting this variable can introduce a noticeable performance impact on all other applications that you run. To set it only for Tcl, you might want to do this instead:$ gcc -shared example.o example_wrap.o -L/home/beazley/projects/lib -lfoo \ -Xlinker -rpath /home/beazley/projects/lib \ -o example.so
Finally, you can use a command such as ldconfig to add additional search paths to the default system configuration (this requires root access and you will need to read the man pages).$ env LD_LIBRARY_PATH=/home/beazley/projects/lib tclsh
On most machines, C++ extension modules should be linked using the C++ compiler. For example:
In addition to this, you may need to include additional library files to make it work. For example, if you are using the Sun C++ compiler on Solaris, you often need to add an extra library -lCrun like this:% swig -c++ -tcl example.i % g++ -c example.cxx % g++ -c example_wrap.cxx -I/usr/local/include % g++ -shared example.o example_wrap.o -o example.so
Of course, the extra libraries to use are completely non-portable---you will probably need to do some experimentation.% swig -c++ -tcl example.i % CC -c example.cxx % CC -c example_wrap.cxx -I/usr/local/include % CC -G example.o example_wrap.o -L/opt/SUNWspro/lib -o example.so -lCrun
Sometimes people have suggested that it is necessary to relink the Tcl interpreter using the C++ compiler to make C++ extension modules work. In the experience of this author, this has never actually appeared to be necessary. Relinking the interpreter with C++ really only includes the special run-time libraries described above---as long as you link your extension modules with these libraries, it should not be necessary to rebuild Tcl.
If you aren't entirely sure about the linking of a C++ extension, you might look at an existing C++ program. On many Unix machines, the ldd command will list library dependencies. This should give you some clues about what you might have to include when you link your extension module. For example:
$ ldd swig libstdc++-libc6.1-1.so.2 => /usr/lib/libstdc++-libc6.1-1.so.2 (0x40019000) libm.so.6 => /lib/libm.so.6 (0x4005b000) libc.so.6 => /lib/libc.so.6 (0x40077000) /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x40000000) $
As a final complication, a major weakness of C++ is that it does not define any sort of standard for binary linking of libraries. This means that C++ code compiled by different compilers will not link together properly as libraries nor is the memory layout of classes and data structures implemented in any kind of portable manner. In a monolithic C++ program, this problem may be unnoticed. However, in Tcl, it is possible for different extension modules to be compiled with different C++ compilers. As long as these modules are self-contained, this probably won't matter. However, if these modules start sharing data, you will need to take steps to avoid segmentation faults and other erratic program behavior. If working with lots of software components, you might want to investigate using a more formal standard such as COM.
To utilize 64-bits, the Tcl executable will need to be recompiled as a 64-bit application. In addition, all libraries, wrapper code, and every other part of your application will need to be compiled for 64-bits. If you plan to use other third-party extension modules, they will also have to be recompiled as 64-bit extensions.
If you are wrapping commercial software for which you have no source code, you will be forced to use the same linking standard as used by that software. This may prevent the use of 64-bit extensions. It may also introduce problems on platforms that support more than one linking standard (e.g., -o32 and -n32 on Irix).
If you have a function "bar" in the SWIG file, the prefix option will append the prefix to the name when creating a command and call it "Foo_bar".swig -tcl -prefix Foo example.i
By default, the name of the namespace will be the same as the module name, but you can override it using the -prefix option.swig -tcl -namespace example.i
When the -namespace option is used, objects in the module are always accessed with the namespace name such as Foo::bar.
Now, assuming all went well, SWIG will be automatically invoked when you build your project. Any changes made to the interface file will result in SWIG being automatically invoked to produce a new version of the wrapper file. To run your new Tcl extension, simply run tclsh or wish and use the load command. For example :
MSDOS > tclsh80 % load example.dll % fact 4 24 %
To build the extension, run NMAKE (you may need to run vcvars32 first). This is a pretty minimal Makefile, but hopefully its enough to get you started. With a little practice, you'll be making lots of Tcl extensions.# Makefile for building various SWIG generated extensions SRCS = example.c IFILE = example INTERFACE = $(IFILE).i WRAPFILE = $(IFILE)_wrap.c # Location of the Visual C++ tools (32 bit assumed) TOOLS = c:\msdev TARGET = example.dll CC = $(TOOLS)\bin\cl.exe LINK = $(TOOLS)\bin\link.exe INCLUDE32 = -I$(TOOLS)\include MACHINE = IX86 # C Library needed to build a DLL DLLIBC = msvcrt.lib oldnames.lib # Windows libraries that are apparently needed WINLIB = kernel32.lib advapi32.lib user32.lib gdi32.lib comdlg32.lib winspool.lib # Libraries common to all DLLs LIBS = $(DLLIBC) $(WINLIB) # Linker options LOPT = -debug:full -debugtype:cv /NODEFAULTLIB /RELEASE /NOLOGO / MACHINE:$(MACHINE) -entry:_DllMainCRTStartup@12 -dll # C compiler flags CFLAGS = /Z7 /Od /c /nologo TCL_INCLUDES = -Id:\tcl8.0a2\generic -Id:\tcl8.0a2\win TCLLIB = d:\tcl8.0a2\win\tcl80.lib tcl:: ..\..\swig -tcl -o $(WRAPFILE) $(INTERFACE) $(CC) $(CFLAGS) $(TCL_INCLUDES) $(SRCS) $(WRAPFILE) set LIB=$(TOOLS)\lib $(LINK) $(LOPT) -out:example.dll $(LIBS) $(TCLLIB) example.obj example_wrap.obj
Will be used in Tcl like this :%module example int foo(int a); double bar (double, double b = 3.0); ...
There isn't much more to say...this is pretty straightforward.set a [foo 2] set b [bar 3.5 -1.5] set b [bar 3.5] # Note : default argument is used
Compatibility Note: Variable tracing is currently supported for all C/C++ datatypes. In older versions of SWIG, only variables of type int, double, and char * could be linked. All other types were accessed using special function calls.// example.i %module example ... double My_variable; ... # Tcl script puts $My_variable # Output value of C global variable set My_variable 5.5 # Change the value
is accessed as follows:%module example #define FOO 42
No attempt is made to enforce the read-only nature of a constant. Therefore, a user could reassign the value if they wanted. You will just have to be careful.% puts $FOO 42 %
A peculiarity of installing constants as variables is that it is necessary to use the Tcl global statement to access constants in procedure bodies. For example:
If a program relies on a lot of constants, this can be extremely annoying. To fix the problem, consider using the following typemap rule:proc blah {} { global FOO bar $FOO }
When applied to an input argument, the CONSTANT rule allows a constant to be passed to a function using its actual value or a symbolic identifier name. For example:%apply int CONSTANT { int x }; #define FOO 42 ... void bar(int x);
When an identifier name is given, it is used to perform an implicit hash-table lookup of the value during argument conversion. This allows the global statement to be ommitted.proc blah {} { bar FOO }
A NULL pointer is represented by the string "NULL". NULL pointers can also be explicitly created as follows :_100f8e2_p_Vector
As much as you might be inclined to modify a pointer value directly from Tcl, don't. The hexadecimal encoding is not necessarily the same as the logical memory address of the underlying object. Instead it is the raw byte encoding of the pointer value. The encoding will vary depending on the native byte-ordering of the platform (i.e., big-endian vs. little-endian). Similarly, don't try to manually cast a pointer to a new type by simply replacing the type-string. This is may not work like you expect and it is particularly dangerous when casting C++ objects. If you need to cast a pointer or change its value, consider writing some helper functions instead. For example:_0_p_Vector
If you need to type-cast a lot of objects, it may indicate a serious weakness in your design. Also, if working with C++, you should always try to use the new C++ style casts. For example, in the above code, the C-style cast may return a bogus result whereas as the C++-style cast will return NULL if the conversion can't be performed.%inline %{ /* C-style cast */ Bar *FooToBar(Foo *f) { return (Bar *) f; } /* C++-style cast */ Foo *BarToFoo(Bar *b) { return dynamic_cast<Foo*>(b); } Foo *IncrFoo(Foo *f, int i) { return f+i; } %}
gets mapped into the following collection of C functions :struct Vector { double x,y,z; };
These functions are then used in the resulting Tcl interface. For example :double Vector_x_get(Vector *obj) double Vector_x_set(Vector *obj, double x) double Vector_y_get(Vector *obj) double Vector_y_set(Vector *obj, double y) double Vector_z_get(Vector *obj) double Vector_z_set(Vector *obj, double z)
# v is a Vector that got created somehow % Vector_x_get $v 3.5 % Vector_x_set $v 7.8 # Change x component
Similar access is provided for unions and the data members of C++ classes.
class List { public: List(); ~List(); int search(char *item); void insert(char *item); void remove(char *item); char *get(int n); int length; static void print(List *l); };
When wrapped by SWIG, the following functions are created :
Within Tcl, we can use the functions as follows :List *new_List(); void delete_List(List *l); int List_search(List *l, char *item); void List_insert(List *l, char *item); void List_remove(List *l, char *item); char *List_get(List *l, int n); int List_length_get(List *l); int List_length_set(List *l, int n); void List_print(List *l);
C++ objects are really just pointers (which are represented as strings). Member functions and data are accessed by simply passing a pointer into a collection of accessor functions that take the pointer as the first argument.% set l [new_List] % List_insert $l Ale % List_insert $l Stout % List_insert $l Lager % List_print $l Lager Stout Ale % puts [List_length_get $l] 3 % puts $l _1008560_p_List %
While somewhat primitive, the low-level SWIG interface provides direct and flexible access to almost any C++ object. As it turns out, it is possible to do some rather amazing things with this interface as will be shown in some of the later examples. SWIG also generates an object-based interface that can be used in addition to the basic interface just described here.
Using the object oriented interface requires no additional modifications or recompilation of the SWIG module (the functions are just used differently).class List { public: List(); ~List(); int search(char *item); void insert(char *item); void remove(char *item); char *get(int n); int length; static void print(List *l); };
MyObject o # Creates a new object named `o' MyObject o -this $objptr # Turn a pointer to an existing C++ object into a # Tcl object named `o' MyObject -this $objptr # Turn the pointer $objptr into a Tcl "object" MyObject -args args # Create a new object and pick a name for it. A handle # will be returned and is the same as the pointer value. MyObject # The same as MyObject -args, but for constructors that # take no arguments.
Thus, for our List class, you can create new List objects as follows :
List l # Create a new list l set listptr [new_List] # Create a new List using low level interface List l2 -this $listptr # Turn it into a List object named `l2' set l3 [List] # Create a new list. The name of the list is in $l3 List -this $listptr # Turn $listptr into a Tcl object of the same name
Assuming you're not completely confused at this point, the best way to think of this is that there are really two different ways of representing an object. One approach is to simply use the pointer value as the name of an object. For example :
The second approach is to allow you to pick a name for an object such as "foo". The different types of constructors are really just a mechanism for using either approach._100e8f8_p_List
Or if you let SWIG generate the name of the object, it works like this:% List l % l insert "Bob" % l insert "Mary" % l search "Dave" 0 % ...
% set l [List] % $l insert "Bob" # Note $l contains the name of the object % $l insert "Mary" % $l search "Dave" 0 %
It is also possible to explicitly delete the object using the delete method. For example:% rename l "" # Destroy list object `l'
If applicable, SWIG will automatically call the corresponding C/C++ destructor when the object is destroyed.% l -delete
The cget method currently only allows retrieval of one member at a time. Extracting multiple members will require repeated calls.% l cget -length # Get the length of the list 13
The member -this contains the pointer to the object that is compatible with other SWIG functions. Thus, the following call would be legal
% List l # Create a new list object % l insert Mike % List_print [l cget -this] # Print it out using low-level function
In a structure such as the following :% l configure -length 10 # Change length to 10 (probably not a good idea, but # possible).
you can change the value of all or some of the members as follows :struct Vector { double x, y, z; };
% v configure -x 3.5 -y 2 -z -1.0
The order of attributes does not matter.
To handle object ownership, two object methods are available:
When Tcl owns an object, it is released when the Tcl variable is destroyed. Otherwise, the Tcl variable is destroyed without calling the corresponding C/C++ destructor.% obj -disown # Release ownership % obj -acquire # Acquire ownership
Here is a script that illustrates how these things work :
# Example 1 : Using a named object List l # Create a new list l insert Dave # Call some methods l insert Jane l insert Pat List_print [l cget -this] # Call a static method (which requires the pointer value) # Example 2: Let SWIG pick a name set l [List] # Create a new list $l insert Dave # Call some methods $l insert Jane $l insert Pat List_print $l # Call static method (name of object is same as pointer) # Example 3: Already existing object set l [new_List] # Create a raw object using low-level interface List_insert $l Dave # Call some methods (using low-level functions) List -this $l # Turn it into a Tcl object instead $l insert Jane $l insert Part List_print $l # Call static method (uses pointer value as before).
or perhapsvoid add(int x, int y, int *result) { *result = x + y; }
The easiest way to handle these situations is to use the typemaps.i file. For example:int sub(int *x, int *y) { return *x+*y; }
In Tcl, this allows you to pass simple values instead of pointer. For example:%module example %include "typemaps.i" void add(int, int, int *OUTPUT); int sub(int *INPUT, int *INPUT);
Notice how the INPUT parameters allow integer values to be passed instead of pointers and how the OUTPUT parameter creates a return result.set a [add 3 4] puts $a 7
If you don't want to use the names INPUT or OUTPUT, use the %apply directive. For example:
%module example %include "typemaps.i" %apply int *OUTPUT { int *result }; %apply int *INPUT { int *x, int *y}; void add(int x, int y, int *result); int sub(int *x, int *y);
If a function mutates one of its parameters like this,
you can use INOUT like this:void negate(int *x) { *x = -(*x); }
In Tcl, a mutated parameter shows up as a return value. For example:%include "typemaps.i" ... void negate(int *INOUT);
set a [negate 3] puts $a -3
The most common use of these special typemap rules is to handle functions that return more than one value. For example, sometimes a function returns a result as well as a special error code:
To wrap such a function, simply use the OUTPUT rule above. For example:/* send message, return number of bytes sent, along with success code */ int send_message(char *text, int len, int *success);
When used in Tcl, the function will return multiple values as a list.%module example %include "typemaps.i" %apply int *OUTPUT { int *success }; ... int send_message(char *text, int *success);
Another common use of multiple return values are in query functions. For example:set r [send_message "Hello World"] set bytes [lindex $r 0] set success [lindex $r 1]
To wrap this, you might use the following:void get_dimensions(Matrix *m, int *rows, int *columns);
Now, in Perl:%module example %include "typemaps.i" %apply int *OUTPUT { int *rows, int *columns }; ... void get_dimensions(Matrix *m, int *rows, *columns);
set dim [get_dimensions $m] set r [lindex $dim 0] set c [lindex $dim 1]
class RangeError {}; // Used for an exception class DoubleArray { private: int n; double *ptr; public: // Create a new array of fixed size DoubleArray(int size) { ptr = new double[size]; n = size; } // Destroy an array ~DoubleArray() { delete ptr; } // Return the length of the array int length() { return n; } // Get an item from the array and perform bounds checking. double getitem(int i) { if ((i >= 0) && (i < n)) return ptr[i]; else throw RangeError(); } // Set an item in the array and perform bounds checking. void setitem(int i, double val) { if ((i >= 0) && (i < n)) ptr[i] = val; else { throw RangeError(); } } };
The functions associated with this class can throw a C++ range exception for an out-of-bounds array access. We can catch this in our Tcl extension by specifying the following in an interface file :
%exception { try { $action // Gets substituted by actual function call } catch (RangeError) { Tcl_SetStringObj(tcl_result,"Array index out-of-bounds"); return TCL_ERROR; } }
As shown, the exception handling code will be added to every wrapper function. Since this is somewhat inefficient. You might consider refining the exception handler to only apply to specific methods like this:
In this case, the exception handler is only attached to methods and functions named getitem and setitem.%exception getitem { try { $action } catch (RangeError) { Tcl_SetStringObj(tcl_result,"Array index out-of-bounds"); return TCL_ERROR; } } %exception setitem { try { $action } catch (RangeError) { Tcl_SetStringObj(tcl_result,"Array index out-of-bounds"); return TCL_ERROR; } }
If you had a lot of different methods, you can avoid extra typing by using a macro. For example:
Since SWIG's exception handling is user-definable, you are not limited to C++ exception handling. See the chapter on "Customization Features" for more examples.%define RANGE_ERROR { try { $action } catch (RangeError) { Tcl_SetStringObj(tcl_result,"Array index out-of-bounds"); return TCL_ERROR; } } %enddef %exception getitem RANGE_ERROR; %exception setitem RANGE_ERROR;
Before proceeding, it should be stressed that typemaps are not a required part of using SWIG---the default wrapping behavior is enough in most cases. Typemaps are only used if you want to change some aspect of the primitive C-Tcl interface.
%module example %typemap(in) int { if (Tcl_GetIntFromObj(interp,$input,&$1) == TCL_ERROR) return TCL_ERROR; printf("Received an integer : %d\n",$1); } extern int fact(int n);
Typemaps are always associated with some specific aspect of code generation. In this case, the "in" method refers to the conversion of input arguments to C/C++. The datatype int is the datatype to which the typemap will be applied. The supplied C code is used to convert values. In this code a number of special variable prefaced by a $ are used. The $1 variable is placeholder for a local variable of type int. The $input variable is the input object of type Tcl_Obj *.
When this example is compiled into a Tcl module, it operates as follows:
% load ./example.so % fact 6 Received an integer : 6 720
In this example, the typemap is applied to all occurrences of the int datatype. You can refine this by supplying an optional parameter name. For example:
In this case, the typemap code is only attached to arguments that exactly match int n.%module example %typemap(in) int n { if (Tcl_GetIntFromObj(interp,$input,&$1) == TCL_ERROR) return TCL_ERROR; printf("n = %d\n",$1); } extern int fact(int n);
The application of a typemap to specific datatypes and argument names involves more than simple text-matching--typemaps are fully integrated into the SWIG type-system. When you define a typemap for int, that typemap applies to int and qualified variations such as const int. In addition, the typemap system follows typedef declarations. For example:
However, the matching of typedef only occurs in one direction. If you defined a typemap for Integer, it is not applied to arguments of type int.%typemap(in) int n { if (Tcl_GetIntFromObj(interp,$input,&$1) == TCL_ERROR) return TCL_ERROR; printf("n = %d\n",$1); } typedef int Integer; extern int fact(Integer n); // Above typemap is applied
Typemaps can also be defined for groups of consecutive arguments. For example:
When a multi-argument typemap is defined, the arguments are always handled as a single Tcl object. This allows the function to be used like this (notice how the length parameter is ommitted):%typemap(in) (char *str, int len) { $1 = Tcl_GetStringFromObj($input,&$2); }; int count(char c, char *str, int len);
% count e "Hello World" 1
The following list details all of the typemap methods that can be used by the Tcl module:%typemap(out) int { Tcl_SetObjResult(interp,Tcl_NewIntObj($1)); }
%typemap(in)
Converts Tcl objects to input function arguments%typemap(out)
Converts return value of a C function to a Tcl object%typemap(varin)
Assigns a C global variable from a Tcl object%typemap(varout)
Returns a C global variable as a Tcl object%typemap(freearg)
Cleans up a function argument (if necessary)%typemap(argout)
Output argument processing%typemap(ret)
Cleanup of function return values%typemap(consttab)
Creation of Tcl constants (constant table)%typemap(constcode)
Creation of Tcl constants (init function)%typemap(memberin)
Setting of structure/class member data%typemap(globalin)
Setting of C global variables%typemap(check)
Checks function input values.%typemap(default)
Set a default value for an argument (making it optional).%typemap(ignore)
Ignore an argument, but initialize its value.%typemap(arginit)
Initialize an argument to a value before any conversions occur.Examples of these methods will appear shortly.
$1
A C local variable corresponding to the actual type specified in the %typemap directive. For input values, this is a C local variable that's supposed to hold an argument value. For output values, this is the raw result that's supposed to be returned to Tcl.
$input
A Tcl_Obj * holding a raw Tcl object with an argument or variable value.
$result
A Tcl_Obj * that holds the result to be returned to Tcl.
$1_name
The parameter name that was matched.
$1_type
The actual C datatype matched by the typemap.
$1_ltype
An assignable version of the datatype matched by the typemap (a type that can appear on the left-hand-side of a C assignment operation). This type is stripped of qualifiers and may be an altered version of $1_type. All arguments and local variables in wrapper functions are declared using this type so that their values can be properly assigned.$symname
The Tcl name of the wrapper function being created.
In Tcl:%module argv // This tells SWIG to treat char ** as a special case %typemap(in) char ** { Tcl_Obj **listobjv; int nitems; int i; if (Tcl_ListObjGetElements(interp, $input, &nitems, &listobjv) == TCL_ERROR) { return TCL_ERROR; } $1 = (char **) malloc((nitems+1)*sizeof(char *)); for (i = 0; i < nitems; i++) { $1[i] = Tcl_GetStringFromObj(listobjv[i],0); } $1[i] = 0; } // This gives SWIG some cleanup code that will get called after the function call %typemap(freearg) char ** { if ($1) { free($1); } } // Now a test functions %inline %{ int print_args(char **argv) { int i = 0; while (argv[i]) { printf("argv[%d] = %s\n", i,argv[i]); i++; } return i; } %} %include tclsh.i
% print_args {John Guido Larry} argv[0] = John argv[1] = Guido argv[2] = Larry 3
When wrapped, SWIG matches the argout typemap to the "double *outvalue" argument. The "ignore" typemap tells SWIG to simply ignore this argument when generating wrapper code. As a result, a Tcl function using these typemaps will work like this :// A typemap defining how to return an argument by appending it to the result %typemap(argout) double *outvalue { Tcl_Obj *o = Tcl_NewDoubleObj($1); Tcl_ListObjAppendElement(interp,$result,o); } // A typemap telling SWIG to ignore an argument for input // However, we still need to pass a pointer to the C function %typemap(ignore) double *outvalue (double temp) { $1 = &temp; } // Now a function returning two values int mypow(double a, double b, double *outvalue) { if ((a < 0) || (b < 0)) return -1; *outvalue = pow(a,b); return 0; };
% mypow 2 3 # Returns two values, a status value and the result 0 8 %
Integers
Floating PointTcl_Obj *Tcl_NewIntObj(int Value); void Tcl_SetIntObj(Tcl_Obj *obj, int Value); int Tcl_GetIntFromObj(Tcl_Interp *, Tcl_Obj *obj, int *ip);
StringsTcl_Obj *Tcl_NewDoubleObj(double Value); void Tcl_SetDoubleObj(Tcl_Obj *obj, double value); int Tcl_GetDoubleFromObj(Tcl_Interp *, Tcl_Obj *o, double *dp);
ListsTcl_Obj *Tcl_NewStringObj(char *str, int len); void Tcl_SetStringObj(Tcl_Obj *obj, char *str, int len); char *Tcl_GetStringFromObj(Tcl_Obj *obj, int *len); void Tcl_AppendToObj(Tcl_Obj *obj, char *str, int len);
ObjectsTcl_Obj *Tcl_NewListObj(int objc, Tcl_Obj *objv); int Tcl_ListObjAppendList(Tcl_Interp *, Tcl_Obj *listPtr, Tcl_Obj *elemListPtr); int Tcl_ListObjAppendElement(Tcl_Interp *, Tcl_Obj *listPtr, Tcl_Obj *element); int Tcl_ListObjGetElements(Tcl_Interp *, Tcl_Obj *listPtr, int *objcPtr, Tcl_Obj ***objvPtr); int Tcl_ListObjLength(Tcl_Interp *, Tcl_Obj *listPtr, int *intPtr); int Tcl_ListObjIndex(Tcl_Interp *, Tcl_Obj *listPtr, int index, Tcl_Obj_Obj **objptr); int Tcl_ListObjReplace(Tcl_Interp *, Tcl_Obj *listPtr, int first, int count, int objc, Tcl_Obj *objv);
Tcl_Obj *Tcl_DuplicateObj(Tcl_Obj *obj); void Tcl_IncrRefCount(Tcl_Obj *obj); void Tcl_DecrRefCount(Tcl_Obj *obj); int Tcl_IsShared(Tcl_Obj *obj);
Integer conversion
%typemap(in) int, short, long { int temp; if (Tcl_GetIntFromObj(interp, $input, &temp) == TCL_ERROR) return TCL_ERROR; $1 = ($1_ltype) temp; }
Floating point conversion%typemap(out) int, short, long { Tcl_SetIntObj($result,(int) $1); }
%typemap(in) float, double { double temp; if (Tcl_GetDoubleFromObj(interp, $input, &temp) == TCL_ERROR) return TCL_ERROR; $1 = ($1_ltype) temp; }
String Conversion%typemap(out) float, double { Tcl_SetDoubleObj($result, $1); }
%typemap(in) char * { int len; $1 = Tcl_GetStringFromObj(interp, &len); } }
%typemap(out) char * { Tcl_SetStringObj($result,$1); }
int SWIG_ConvertPtr(Tcl_Interp *interp, Tcl_Obj *obj, void **ptr, swig_type_info *ty, int flags)
Converts a Tcl object obj to a C pointer. The result of the conversion is placed into the pointer located at ptr. ty is a SWIG type descriptor structure. flags is used to handle error checking and other aspects of conversion. It is currently reserved for future expansion. Returns 0 on success and -1 on error.
Tcl_Obj *SWIG_NewPointerObj(void *ptr, swig_type_info *ty, int flags)
Creates a new Tcl pointer object. ptr is the pointer to convert, ty is the SWIG type descriptor structure that describes the type, and own is a flag reserved for future expansion.Both of these functions require the use of a special SWIG type-descriptor structure. This structure contains information about the mangled name of the datatype, type-equivalence information, as well as information about converting pointer values under C++ inheritance. For a type of Foo *, the type descriptor structure is usually accessed as follows:
In a typemap, the type descriptor should always be accessed using the special typemap variable $1_descriptor. For example:Foo *f; if (SWIG_ConvertPtr(interp,$input, (void **) &f, SWIGTYPE_p_Foo, 0) == -1) return NULL; Tcl_Obj *; obj = SWIG_NewPointerObj(f, SWIGTYPE_p_Foo, 0);
%typemap(in) Foo * { if ((SWIG_ConvertPtr(interp, $input,(void **) &$1, $1_descriptor,0)) == -1) return NULL; }
If necessary, the descriptor for any type can be obtained using the $descriptor() macro in a typemap. For example:
%typemap(in) Foo * { if ((SWIG_ConvertPtr(interp,$input,(void **) &$1, $descriptor(Foo *), 0)) == -1) return NULL; }
After building the SWIG generated module, you need to execute the "pkg_mkIndex" command inside tclsh. For example :% swig -tcl -pkgversion 2.3 example.i
This creates a file "pkgIndex.tcl" with information about the package. To use yourunix > tclsh % pkg_mkIndex . example.so % exit
package, you now need to move it to its own subdirectory which has the same name as the package. For example :
./example/ pkgIndex.tcl # The file created by pkg_mkIndex example.so # The SWIG generated module
Finally, assuming that you're not entirely confused at this point, make sure that the example subdirectory is visible from the directories contained in either the tcl_library or auto_path variables. At this point you're ready to use the package as follows :
unix > tclsh % package require example % fact 4 24 %
If you're working with an example in the current directory and this doesn't work, do this instead :
unix > tclsh % lappend auto_path . % package require example % fact 4 24
As a final note, most SWIG examples do not yet use the package commands. For simple extensions it may be easier just to use the load command instead.
While these could be called directly, we could also write a Tcl script like this :/* File : array.i */ %module array %inline %{ double *new_double(int size) { return (double *) malloc(size*sizeof(double)); } void delete_double(double *a) { free(a); } double get_double(double *a, int index) { return a[index]; } void set_double(double *a, int index, double val) { a[index] = val; } int *new_int(int size) { return (int *) malloc(size*sizeof(int)); } void delete_int(int *a) { free(a); } int get_int(int *a, int index) { return a[index]; } int set_int(int *a, int index, int val) { a[index] = val; } %}
proc Array {type size} { set ptr [new_$type $size] set code { set method [lindex $args 0] set parms [concat $ptr [lrange $args 1 end]] switch $method { get {return [eval "get_$type $parms"]} set {return [eval "set_$type $parms"]} delete {eval "delete_$type $ptr; rename $ptr {}"} } } # Create a procedure uplevel "proc $ptr args {set ptr $ptr; set type $type;$code}" return $ptr }
Our script allows easy array access as follows :
set a [Array double 100] ;# Create a double [100] for {set i 0} {$i < 100} {incr i 1} { ;# Clear the array $a set $i 0.0 } $a set 3 3.1455 ;# Set an individual element set b [$a get 10] ;# Retrieve an element set ia [Array int 50] ;# Create an int[50] for {set i 0} {$i < 50} {incr i 1} { ;# Clear it $ia set $i 0 } $ia set 3 7 ;# Set an individual element set ib [$ia get 10] ;# Get an individual element $a delete ;# Destroy a $ia delete ;# Destroy ia
The cool thing about this approach is that it makes a common interface for two different types of arrays. In fact, if we were to add more C datatypes to our wrapper file, the Tcl code would work with those as well--without modification. If an unsupported datatype was requested, the Tcl code would simply return with an error so there is very little danger of blowing something up (although it is easily accomplished with an out of bounds array access).
# swig_c++.tcl # Provides a simple object oriented interface using # SWIG's low level interface. # proc new {objectType handle_r args} { # Creates a new SWIG object of the given type, # returning a handle in the variable "handle_r". # # Also creates a procedure for the object and a trace on # the handle variable that deletes the object when the # handle varibale is overwritten or unset upvar $handle_r handle # # Create the new object # eval set handle \[new_$objectType $args\] # # Set up the object procedure # proc $handle {cmd args} "eval ${objectType}_\$cmd $handle \$args" # # And the trace ... # uplevel trace variable $handle_r uw "{deleteObject $objectType $handle}" # # Return the handle so that 'new' can be used as an argument to a procedure # return $handle } proc deleteObject {objectType handle name element op} { # # Check that the object handle has a reasonable form # if {![regexp {_[0-9a-f]*_(.+)_p} $handle]} { error "deleteObject: not a valid object handle: $handle" } # # Remove the object procedure # catch {rename $handle {}} # # Delete the object # delete_$objectType $handle } proc delete {handle_r} { # # A synonym for unset that is more familiar to C++ programmers # uplevel unset $handle_r }
To use this file, we simply source it and execute commands such as "new" and "delete" to manipulate objects. For example :
// list.i %module List %{ #include "list.h" %} // Very simple C++ example class List { public: List(); // Create a new list ~List(); // Destroy a list int search(char *value); void insert(char *); // Insert a new item into the list void remove(char *); // Remove item from list char *get(int n); // Get the nth item in the list int length; // The current length of the list static void print(List *l); // Print out the contents of the list };
Now a Tcl script using the interface...
The cool thing about this example is that it works with any C++ object wrapped by SWIG and requires no special compilation. Proof that a short, but clever Tcl script can be combined with SWIG to do many interesting things.load ./list.so list ; # Load the module source swig_c++.tcl ; # Source the object file new List l $l insert Dave $l insert John $l insert Guido $l remove Dave puts $l length_get delete l