What is the proper way to get the value of Tcl object via Tcl API

[Nicolas Robert]

Hello ,

I have a list like this :
set myList {1 2 3 4 ::oo::Obj10 foo 10 bar}
A method like this :
method get {} {
# Gets object value.
return $_value
}

And my C code (C experts , Close your eyes!) :
// ...
for (int i = 0; i < count; ++i) {
if (Tcl_GetDoubleFromObj(interp, sub_elements[i], &d) == TCL_OK) {
// Do something...
} else if (!strncmp(Tcl_GetString(sub_elements[i]), "::oo::Obj", 9)) {
strcpy(obj, Tcl_GetString(sub_elements[i]));
strcat(obj, " get"); // method get
if (Tcl_Eval(interp, obj) != TCL_OK) {
return TCL_ERROR;
}
Tcl_ListObjAppendElement(interp, data, Tcl_GetObjResult(interp));
} else {
// Do something...
}
}
//...

I'm using 'strncmp' combined with Tcl_Eval.
I would like to know if there is other method to get the value of my object in a list.
My code works but I don’t know if it is correct.
That's how you'd handle it, something like this ?

Thanks
Nicolas

[Rich]

If you want the result of the 'get' call to be in the list, then one
way is to put it there when you create the list:

Create the list this way:

set myList [list 1 2 3 4 [::oo::Obj10 get] foo 10 bar]

And then you don't need to look for strings that look like oo object
names in the list to then try to create a call to that strings get
method.

[clt.to...@dfgh.net]

You might be better off trying to avoid having to guess how to process the list objects.

However given that you are creating and executing a command from Tcl_Objs, consider using Tcl_EvalObjv, and instead of checking that the string value looks like an object name just execute the get method on the Tcl_Obj and check if there was an error.

// set up command object array (consider doing this only once in your application)
// I think this is the correct way to initalize a C array to NULLs ??
Tcl_Obj* cmd[3] = {NULL, NULL, NULL};

// second word of command is "get"
cmd[1] = Tcl_NewStringObj("get", -1);

// make sure the "get" does not disappear at an inopportune time.
Tcl_IncrRefCount(cmd[1]);

// need to decrement the reference count (Tcl_DecrRefCount(cmd[1]);)
// just before the cmd[] array goes out of scope to avoid a memory leak

...

// try executing a get method on the current list entry
// if there is a chance the sub element has a zero reference count (unlikely for a list element),
// increment it here (and remember to decrement it later to avoid a memory leak)
cmd[0] = sub_elements[i];
if (TCL_OK == Tcl_EvalObjv(interp, cmd, 0)) {
DO SOMETHING with the result in interp
} else {
TRY SOMETHING ELSE
}

I did not compile or execute this YMMV

Dave B

[Nicolas Robert]

Le lundi 5 juin 2023 à 17:05:22 UTC+2, clt.to...@dfgh.net a écrit :
> Create the list this way:
> set myList [list 1 2 3 4 [::oo::Obj10 get] foo 10 bar]

@Rich ,
I can't, the goal here is to check each type, so I need to keep the name of the object.

@Dave

If I understand , In that way so in Tcl :
foreach obj $myList {
if {![catch {$obj get} value]} {
# Do something
}
}
Maybe I'm wrong but in pure Tcl, I would never do like that, It's maybe different in C.
That said
Below my C code :
Tcl_Obj* cmd[2];
cmd[1] = Tcl_NewStringObj ("get", -1);
Tcl_IncrRefCount(cmd[1]);

for (int i = 0; i < count; ++i) {

cmd[0] = sub_elements[i];

Tcl_IncrRefCount(cmd[0]);

if (Tcl_EvalObjv(interp, 2, cmd, 0) == TCL_OK) {
Tcl_DecrRefCount(cmd[0]);

Tcl_ListObjAppendElement(interp, data, Tcl_GetObjResult(interp));
} else {
// Do something...
}
}

Tcl_DecrRefCount(cmd[1]);

I’m not sure about myself, it works , but I tested on a list of 20000 items and my performance is bad, my C code is correct ?

Thanks
Nicolas

[Rich]

Nicolas Robert <nicolasro...@gmail.com> wrote:
> Le lundi 5 juin 2023 à 17:05:22 UTC+2, clt.to...@dfgh.net a écrit :
>> Create the list this way:
>> set myList [list 1 2 3 4 [::oo::Obj10 get] foo 10 bar]
>

> I can't, the goal here is to check each type, so I need to keep the
> name of the object.

Then consider changing your list definition:

set myList [list val 1 val 2 val 3 val 4 obj ::oo::Obj10 val foo val 10 val bar]

Then (in Tcl) you could process something like this way:

foreach {type content} $myList {
switch -exact -- $type {
val { # do something with a value }
obj { # do a [$content get] to get the value, then do something
with the value and the object name }
}
}

A similar 'loop' in C could be crafted but I'm not going to attempt to
type that out here (it would likely contain many syntax errors).

[Nicolas Robert]

Rich,

I do not know the type of my strings before testing them via a loop.
So my loop in Tcl is like this :
foreach content $myList {
if {[string is ...]} {...}
if {[info object isa object ...] {...}
}

I’d like to do the same in C.

Nicolas