Tcl interpreter undefined reference error while compiling with gcc

Question

I am new to Tcl scripting and would like to use C to embed Tcl codes. This is the code that I have copied from a website to test the Tcl-C working.

test.c

#include <stdio.h>
#include <tcl.h>
void main ()
{
   Tcl_Interp *myinterp;
   char *action = "set a [expr 5 * 8]; puts $a";
   int status;
   printf ("Your Program will run ... \n");
   myinterp = Tcl_CreateInterp();
   status = Tcl_Eval(myinterp,action);
   printf ("Your Program has completed\n");
   getch();
}

I am using MinGW to compile this file.

I have copied the contents of the C:\Tcl\include folder into the C:\MinGW\include folder as well.

My gcc command for compiling :

gcc -o test.exe test.c

The error message shown :

C:\Users\user\AppData\Local\Temp\ccEHJKCb.o:tcl_connection_test.c:(.text+0x23): undefined reference to `_imp__Tcl_CreateInterp'
C:\Users\user\AppData\Local\Temp\ccEHJKCb.o:tcl_connection_test.c:(.text+0x3d): undefined reference to `_imp__Tcl_Eval'
c:/mingw/bin/../lib/gcc/mingw32/4.8.1/../../../../mingw32/bin/ld.exe: C:\Users\user\AppData\Local\Temp\ccEHJKCb.o: bad reloc address 0x20 in section `.eh_frame'
c:/mingw/bin/../lib/gcc/mingw32/4.8.1/../../../../mingw32/bin/ld.exe: final link failed: Invalid operation
collect2.exe: error: ld returned 1 exit status

I don't seem to have any libtcl file in the Tcl folder.

The Tcl version is ActiveTcl 8.5.15.0.297577.

Any help would be really appreciated.

Answer 1

Your example how to embed Tcl is outdated, and you are missing certain things in your link line (-ltcl85 for example). If you simply add -ltcl85 to your link line it should start to work.

It does not work in your case, because you installed the x64 (64-Bit version) of ActiveTcl, which provides x64 dlls, not 32-Bit ones. But the standard mingw gcc only works with 32-Bit libraries.

So to get this to work:

1. Download the 32-Bit ActiveTcl distribution
2. Compile your code with gcc -o test.exe test.c -Lc:/tcl/lib -Ic:/tcl/include -ltcl86
3. Adjust your path so the c:\tcl\bin\tcl86.dll is found in PATH, make also sure Tcl finds its libdir (set TCL_LIBRARY=c:\tcl\lib\tcl8.6)
4. run your program

But for more complex examples, you still need to initialise the library and a do some boilerplate code, so please call Tcl_FindExecutable(argv[0]); before the call to Tcl_CreateInterp() otherwise a few commands (e.g. clock might just not work as expected).

Have a look at http://www.tcl.tk/cgi-bin/tct/tip/66.html for some more details. Also have a look at the Tcl source distribution and the source for the tclsh shell.

Answer 2

You're very close to getting it right.

The Tcler's Wiki has a few examples, some of which are very confusing to be frank, but this one from this page is the best I've spotted recently. (The comments are mine.)

#include <stdlib.h>
#include <tcl.h>

int main (int argc, char *argv[]) {
    Tcl_Interp *interp;
    const char *script = "proc p1 a { puts $a }";

    // Initialize the Tcl library; ***STRONGLY RECOMMENDED***
    Tcl_FindExecutable(argv[0]);

    // Create the interpreter, the execution context
    interp = Tcl_CreateInterp();

    // Initialise the interpreter
    if (TCL_OK != Tcl_Init(interp)) {
        fprintf(stderr, "Tcl_Init error: %s\n", Tcl_GetStringResult(interp));
        exit(EXIT_FAILURE);
    }

    // Define a procedure
    Tcl_Eval(interp, script);
    fprintf(stderr, "res 1: %s\n", Tcl_GetStringResult(interp));

    // Check if the procedure exists
    Tcl_Eval(interp, "puts [info commands p*]");
    fprintf(stderr, "res 2: %s\n", Tcl_GetStringResult(interp));

    // Call the procedure
    Tcl_Eval(interp, "p1 abc");
    fprintf(stderr, "res 3: %s\n", Tcl_GetStringResult(interp));

    // We could use Tcl_DeleteInterpreter to clean up here, but why bother?  
    return EXIT_SUCCESS;
}

What else were you missing? Simple. You forgot to tell the C compiler to use the Tcl library when building the executable; the compiler (or, more strictly, the linker) is in places a stupid piece of code. The exact option to use to get the linker to add the library in will depend on your system configuration, but is probably going to be -ltcl, -ltcl8.5 or -ltcl8.6; which it is depends on the filename and all sorts of things that we can't check exactly without being on your system. The names do fit a simple pattern though.

It's also possible that you might need to pass the -L option in to tell the linker about additional library locations. (There's an equivalent -I for telling the compiler where to find include files, so you don't have to copy everything into one gigantic unmanageable directory.)

The order of arguments can matter. Libraries should be listed after the source file:

gcc -o test.exe test.c -L/mingw/path/to/library/directory -ltcl86

(If you're using old, unsupported versions of Tcl — why would you do that?! — then the code above won't work because Tcl_Eval then took a writable string. But that was fixed many years ago and upgrading to a current version is the fix.)