Embedded interpreter woes?

[Antti Järvinen]

Dear Sirs,

here is a c-code:
-------------------------------
#include <stdio.h>
#include <wchar.h>
#include <tcl.h>
#include <stdlib.h>

Tcl_Interp *tcl_interp ;
char *the_program = "puts stdout $FooBar\nset a_len [ string length $FooBar ]\nputs stdout $a_len" ;

int main(int argc, char **argv)
{
tcl_interp = Tcl_CreateInterp() ;
if(tcl_interp == NULL) {
fprintf(stderr,"problem") ;
return(-1) ;
}
if(Tcl_Init(tcl_interp) == TCL_ERROR) {
fprintf(stderr,"Tcl_init returns TCL_ERROR?\n") ;
return(-2) ;
}
Tcl_FindExecutable(argv[0]) ;

if(Tcl_SetVar(tcl_interp, "FooBar","Value of FooBar",0)==NULL) {
printf("Tcl_SetVar returns null\n") ;
return(-4) ;
}
printf("The_Program->%s<-\n", the_program) ;
printf("\neval=%d\n",Tcl_Eval(tcl_interp, the_program)) ;
return(0) ;
}

-------------------------------

when run on linux box like this:

$ cc unicodeexample2.c -o unicodeexample2 -ltcl -Wall
$ ./unicodeexample2
The_Program->puts stdout $FooBar
set a_len [ string length $FooBar ]
puts stdout $a_len<-

It prints out:
Value of FooBar
Segmentation fault

gdb points here:

Program received signal SIGSEGV, Segmentation fault.
0x4007f7cc in Tcl_ParseCommand () from /usr/lib/libtcl.so.0
(gdb) where
#0 0x4007f7cc in Tcl_ParseCommand () from /usr/lib/libtcl.so.0
#1 0x400807cb in Tcl_EvalEx () from /usr/lib/libtcl.so.0
#2 0x4008051a in Tcl_EvalTokens () from /usr/lib/libtcl.so.0
#3 0x40080848 in Tcl_EvalEx () from /usr/lib/libtcl.so.0
#4 0x40080b89 in Tcl_Eval () from /usr/lib/libtcl.so.0
#5 0x080487c6 in main ()

now:
what the heck I'm doing wrong?

This very same program works wonders when I start tcl interpreter and
copy-paste this code there. If I remove this statement in [] marks and
replace it with some static value, it works. Seems like spawning of
another interpreter breaks something ; what have I broken and where?

This is tried in redhat linuxen 7.2 and 9, having tcl versions
8.3.3 and 8.3.5.

--
Antti Järvinen, cost...@iki.fi
"concerto for two faggots and orchestra"

[miguel sofer]

Antti Järvinen wrote:
> <snip>

> what the heck I'm doing wrong?

Not sure if this is the source of your problem, but ... the call to
Tcl_FindExecutable() should occur BEFORE the first Tcl_CreateInterp().

Tcl_FindExecutable() does more initialization than its name implies :(

Miguel

[Benjamin Riefenstahl]

Hi Antti,

cost...@iki.fi (Antti Järvinen) writes:
> char *the_program = "puts stdout $FooBar\nset a_len [ string length
> $FooBar ]\nputs stdout $a_len" ;

> [...]

> printf("\neval=%d\n",Tcl_Eval(tcl_interp, the_program)) ;

With older Tcl versions, the actual programs that are passed to
Tcl_Eval() must be in modifiable memory (the code temporarily sets
characters to 0). Try this variable declaration instead:

static char the_program[] =
"puts stdout $FooBar\n"
"set a_len [ string length $FooBar ]\n"
"puts stdout $a_len\n"
;

benny

[Antti Järvinen]

Benjamin Riefenstahl <Benjamin.R...@epost.de> writes:
> With older Tcl versions, the actual programs that are passed to
> Tcl_Eval() must be in modifiable memory (the code temporarily sets
> characters to 0). Try this variable declaration instead:
>
> static char the_program[] =
> "puts stdout $FooBar\n"
> "set a_len [ string length $FooBar ]\n"
> "puts stdout $a_len\n"
> ;

Yes,

first I was wondering that I had some end-of-line issues (\r versus \n)
so I did put the tcl-program into a file that I then did read at runtime and
whoop: the program did what expected. And I was confused as content of the
file then really was exactly the same as I had in my memory buffer, including
end-of-line marks.