New example
git-svn-id: https://swig.svn.sourceforge.net/svnroot/swig/trunk/SWIG@727 626c5289-ae23-0410-ae9c-e8d60b6d4f22
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Dave Beazley
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19
Examples/tcl/variables/Makefile
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19
Examples/tcl/variables/Makefile
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TOP = ../..
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SWIG = $(TOP)/../swig
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SRCS = example.c
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TARGET = my_tclsh
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DLTARGET = example
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INTERFACE = example.i
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all::
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$(MAKE) -f $(TOP)/Makefile SRCS='$(SRCS)' SWIG='$(SWIG)' \
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TARGET='$(DLTARGET)' INTERFACE='$(INTERFACE)' tcl
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static::
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$(MAKE) -f $(TOP)/Makefile SRCS='$(SRCS)' SWIG='$(SWIG)' \
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TARGET='$(TARGET)' INTERFACE='$(INTERFACE)' tclsh
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clean::
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rm -f *_wrap* *.o my_tclsh *~ .~* core *.so *.sl
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check: all
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54
Examples/tcl/variables/example.c
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54
Examples/tcl/variables/example.c
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/* File : example.c */
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/* I'm a file containing some C global variables */
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#include <stdio.h>
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#include <stdlib.h>
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int ivar = 0;
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short svar = 0;
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long lvar = 0;
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unsigned int uivar = 0;
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unsigned short usvar = 0;
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unsigned long ulvar = 0;
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signed char scvar = 0;
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unsigned char ucvar = 0;
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char cvar = 0;
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float fvar = 0;
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double dvar = 0;
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char *strvar = 0;
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int *iptrvar = 0;
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char name[256] = "Dave";
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/* A variable that we will make read-only in the interface */
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int status = 1;
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/* A debugging function to print out their values */
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void print_vars() {
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printf("ivar = %d\n", ivar);
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printf("svar = %d\n", svar);
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printf("lvar = %ld\n", lvar);
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printf("uivar = %u\n", uivar);
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printf("usvar = %u\n", usvar);
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printf("ulvar = %lu\n", ulvar);
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printf("scvar = %d\n", scvar);
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printf("ucvar = %u\n", ucvar);
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printf("fvar = %g\n", fvar);
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printf("dvar = %g\n", dvar);
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printf("cvar = %c\n", cvar);
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printf("strvar = %s\n", strvar ? strvar : "(null)");
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printf("iptrvar = %x\n", iptrvar);
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printf("name = %s\n", name);
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printf("status = %d\n", status);
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}
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/* A function to create an integer (to test iptrvar) */
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int *new_int(int value) {
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int *ip = (int *) malloc(sizeof(int));
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*ip = value;
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return ip;
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}
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31
Examples/tcl/variables/example.i
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31
Examples/tcl/variables/example.i
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/* File : example.i */
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%module example
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/* Some global variable declarations */
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extern int ivar;
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extern short svar;
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extern long lvar;
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extern unsigned int uivar;
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extern unsigned short usvar;
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extern unsigned long ulvar;
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extern signed char scvar;
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extern unsigned char ucvar;
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extern char cvar;
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extern float fvar;
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extern double dvar;
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extern char *strvar;
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extern int *iptrvar;
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extern char name[256];
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/* Some helper functions to make it easier to test */
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extern void print_vars();
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extern int *new_int(int value);
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/* A read-only variable */
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%readonly
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extern int status;
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%readwrite
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63
Examples/tcl/variables/example.tcl
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63
Examples/tcl/variables/example.tcl
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# file: example.tcl
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catch { load ./example.so example} ;# Unix
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catch { load ./example.dll example} ;# Windows
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# Try to set the values of some global variables
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set ivar 42
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set svar -31000
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set lvar 65537
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set uivar 123456
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set usvar 61000
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set ulvar 654321
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set scvar -13
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set ucvar 251
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set cvar "S"
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set fvar 3.14159
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set dvar 2.1828
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set strvar "Hello World"
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set iptrvar [new_int 37]
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# Now print out the values of the variables
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puts "Variables (values printed from Tcl)"
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puts "ivar = $ivar"
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puts "svar = $svar"
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puts "lvar = $lvar"
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puts "uivar = $uivar"
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puts "usvar = $usvar"
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puts "ulvar = $ulvar"
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puts "scvar = $scvar"
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puts "ucvar = $ucvar"
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puts "fvar = $fvar"
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puts "dvar = $dvar"
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puts "cvar = $cvar"
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puts "strvar = $strvar"
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puts "iptrvar = $iptrvar"
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puts "name = $name"
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puts "\nVariables (values printed from C)"
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print_vars
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puts "\nNow I'm going to try and modify some read only variables";
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puts " Tring to set 'name'";
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if { [catch {
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set name "Whoa!"
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puts "Hey, what's going on?!?! This shouldn't work"
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}]} {
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puts "Good."
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}
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puts " Trying to set 'status'";
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if { [catch {
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set status 0
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puts "Hey, what's going on?!?! This shouldn't work"
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}]} {
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puts "Good."
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}
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88
Examples/tcl/variables/index.html
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88
Examples/tcl/variables/index.html
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<html>
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<head>
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<title>SWIG:Examples:tcl:variables</title>
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</head>
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<body bgcolor="#ffffff">
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<tt>SWIG/Examples/tcl/variables/</tt>
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<hr>
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<H2>Wrapping C Global Variables</H2>
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<tt>$Header$</tt><br>
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<p>
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When a C global variable appears in an interface file, SWIG tries to wrap it using a technique
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known as "variable linking." The idea is pretty simple---we try to create a Tcl
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variable that works exactly like you would expect in a Tcl script, but which magically
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retrieves or updates the value of the underlying C variable.
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Click <a href="example.i">here</a> to see a SWIG interface with some variable declarations in it.
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<h2>Manipulating Variables from Tcl</h2>
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Click <a href="example.tcl">here</a> to see a script that updates and prints out the values of
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the variables defined in the above file. Notice how the C global variables work just
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like normal Tcl variables.
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<h2>Key points</h2>
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<ul>
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<li>The <tt>set</tt> statement changes the value of the corresponding C global variable.
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<li>Whenever you access the value of a variable such as <tt>$ivar</tt>, the value
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of the C global variable is read.
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<li>If a C program changes a global variable independently of Tcl, this change is
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automatically reflected in the Tcl variable (i.e., reads will always return the
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most up to date value of the variable).
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<li>When a global variable has the type "<tt>char *</tt>", SWIG manages it as a character
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string. However, whenever the value of such a variable is set from Tcl, the old
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value is destroyed using <tt>free()</tt> or <tt>delete</tt> (the choice of which depends
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on whether or not SWIG was run with the -c++ option).
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<li><tt>signed char</tt> and <tt>unsigned char</tt> are handled as small 8-bit integers.
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<li>Array variables such as '<tt>char name[256]</tt>' are read-only variables because
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SWIG doesn't really know how to change the "value" of an array. You can work
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around this by writing some kind of helper function in the SWIG interface.
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For example:
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<blockquote>
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<pre>
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%inline %{
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void set_name(char *newname) {
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strncpy(name,newname,256);
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}
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%}
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</pre>
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</blockquote>
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</ul>
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<h2>Creating read-only variables</h2>
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The <tt>%readonly</tt> and <tt>%readwrite</tt> directives can be used to
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specify a collection of read-only variables. For example:
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<blockquote>
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<pre>
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%readonly
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int status;
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double blah;
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...
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%readwrite
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</pre>
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</blockquote>
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The <tt>%readonly</tt> directive remains in effect until it is explicitly disabled
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using the <tt>%readwrite</tt> directive.
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<h2>Comments</h2>
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<ul>
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<li>Management of global variables is one of the most problematic aspects
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of C/C++ wrapping because the scripting interface and resulting memory management
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is much trickier than simply creating a wrapper function.
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<p>
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<li>You may be better off hiding global variables behind a function based
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interface.
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</ul>
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</body>
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</html>
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<hr>
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