The following questions tend to be asked regularly on the comp.lang.tcl newsgroup:
At a high level, there are three different solutions to consider.
While the text "Why adding Tcl calls to a C/C++ application is a bad idea" is an interesting dialog concerning the appropriate approach to performing this task, where can one find specific coding examples and documentation regarding what one needs to do, in a C program, if one needs to create an interpreter and then execute tcl commands making use of that interpreter.
Well, one example comes out of the box with both Tcl and Tk. Take a look at the tcl/unix/tclAppInit.c (or tcl/win/tclAppInit.c) files in the tcl source distribution (which is the mainline C module for the tclsh command), and in the Tk source distribution, tk/unix/tkAppInit.c or tk/win/winMain.c (I don't understand why the name difference here...). For MacOS, see tk/mac/tkMacAppInit.c and tk/macosx/tkMacOSXAppInit.c (again, I don't understand the reasoning for file name changes). These provide at least a basic skeleton for initializing an interpreter. Unfortunately, they leave you in an interpretive mode which most people don't want to happen. So another example is needed.
I do know there are two kinds of Tcl actions one can invoke from C/C++ Since Tcl is just a C library, some Tcl actions can be invoked by calling the appropriate Tcl function call.
However, some things in Tcl must be done by invoking Tcl_Eval, after appropriately setting up a Tcl interpreter.
Can someone provide some sample C or C++ code that shows setting up the interpreter, then perhaps invoking things each way?
A dream scenario would do this for Tcl/Tk since that is a superset of the same kind of request for Tcl...
AM Here is some (massaged) code that I use in one application. The idea is:
It does not use the Tcl script library, only the basic built-in commands are available, but this is a very simple set-up after all.
The function InitScript() is used to set up a script library private to the application and to get a functioning Tcl interpreter. The function EvalScriptCommand() is used elsewhere and simply wraps the details so that I do not need to use Tcl routines everywhere.
#include <stdlib.h>
/*
* Static global data
*/
static Tcl_Interp * tcl_interp ; /* Script interpreter */
int
InitScript(
void /* Nothing */
) /* Return okay or not */
{
char * pstr ;
FILE * infile ;
int retval ;
int rc ;
size_t filesize ;
tcl_interp = Tcl_CreateInterp() ;
if ( tcl_interp == NULL )
{
fprintf( stderr, "Could not create interpreter!\n" ) ;
return 1 ;
}
/* Register the commands specific to my application
Tcl_CreateObjCommand( tcl_interp, "session", GppSessionCmd,
(ClientData) NULL, GppDummyDestroy ) ;
/* Read the configuration file with specific script code
(in reality, I use a function that searches for the file and opens it!
Hence I need to do more work ... If you have the file name, then use
Tcl_EvalFile()!)
*/
infile = fopen( "scripts.conf", "r" ) ;
if ( infile == NULL )
{
return 1 ;
}
/* Now, read the whole file ...
*/
fseek( infile, 0L, SEEK_END ) ;
filesize = ftell( infile ) ;
pstr = (char * ) malloc( (filesize+1) * sizeof(char) ) ;
if ( pstr == NULL )
{
return 1;
}
fseek( infile, 0L, SEEK_SET ) ;
fread( pstr, filesize, 1, infile ) ;
pstr[filesize] = '\0' ;
rc = Tcl_Eval( tcl_interp, pstr ) ;
if ( rc != TCL_OK )
{
fprintf( stderr, "Error loading script library\n" ) ;
return 1 ;
}
free( pstr ) ;
return 0;
}
/* Function for encapsulating the details
*/
EvalScriptCommand(
char * command )
{
if ( Tcl_Eval( tcl_interp, command ) == TCL_OK )
{
return 0 ;
}
else
{
return 1 ;
}
}
//compile with g++ and run using ./execDavid Gravereaux writes, on comp.lang.tcl, this code fragment for invoking Tcl from a C program:
Tcl_Interp *interp;
int Init (char *argv0)
{
Tcl_FindExecutable(argv0);
interp = Tcl_CreateInterp();
if (Tcl_Init(interp) != TCL_OK) {
return TCL_ERROR;
}
return TCL_OK;
}
void TearDown () {Tcl_Finalize();}
int EvalFile (char *fileName)
{
return Tcl_EvalFile(interp, fileName);
}
If EvalFile() returns TCL_ERROR, get the error with Tcl_GetStringResult() .
Lectus I've beeing experimenting with "GUIfying" C/C++ programs using Tcl/Tk. Here is how to do it (I tried to make the example simple so it's easy to understand):
C++ code:
#include <iostream>
#include <sstream>
#include <string>
// The procedure to provide the add function
void add(string x, string y)
{
int ix=0;
int iy=0;
// We use stringstream to convert from string to int.
std::stringstream ssx(x);
std::stringstream ssy(y);
ssx >> ix;
ssy >> iy;
// Output the result to stdout.
std::cout << ix+iy << std::endl;
}
// We'll access C or C++ code by passing parameters to the command line program
int main(int argc, char **argv)
{
// Test if we have all args
if (argc < 4)
{
std::cout << "Error" << std::endl;
return 1;
}
// Get the operator and check to see if it's +
std::string opt = argv[1];
if (opt == "+")
{
// Yes, it is, so call add function.
add(argv[2],argv[3]);
}
return 0;
}compiled with $ clang++ test.cpp -o test
And here is the Tcl/TK code with the GUI part:
package require Tk
ttk::label .x -text "X: "
ttk::entry .ex -textvar x
ttk::label .y -text "Y: "
ttk::entry .ey -textvar y
ttk::button .badd -text "Add"
ttk::label .res -text "Result: "
grid .x .ex -padx 5 -pady 2.5
grid .y .ey .badd -padx 5 -pady 2.5
grid .res -padx 5 -pady 2.5
focus .ex
.badd config -command {
if {[catch {open [list "|./test" + $x $y] "r"} fd]} {
puts "Couldn't open pipe."
exit
}
set z [gets $fd]
close $fd
.res config -text "Result: $z"
}Note: Tested on FreeBSD and Linux. On windows you probably need to replace "./test" for "test".