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[comment {-*- mode: tcl ; fill-column: 90 -*-}]
[list_begin enumerated]
[enum][vset base][example {
critcl::cproc sqrt {
Tcl_Interp* interp
double x
} object0 {
if (x < 0) {
Tcl_SetObjResult (interp, Tcl_ObjPrintf ("Expected double >=0, but got \"%d\"", x));
Tcl_SetErrorCode (interp, "EXAMPLE", "BAD", "DOMAIN", NULL);
return NULL;
}
return Tcl_NewDoubleObj(sqrt(x));
}
}][vset rebuild]
[enum] In standard C-based packages commands signal errors by returning [const TCL_ERROR],
placing the error message as the interpreter result, and maybe providing an error code via
[fun Tcl_SetErrorCode].
[enum] When using [cmd critcl::cproc] this is limited and hidden.
[enum] The simple and string types for results do not allow failure. The value is returned
to the translation layer, converted into the interpreter result and then reported as
success ([const TCL_OK]).
[enum] The object types on the other hand do allow for failure.
Return a [const NULL] value to signal failure to the translation layer, which then reports
this to the interpreter via the standard [const TCL_ERROR].
[enum] [emph Attention] Setting the desired error message and code into the interpreter is
still the responsibility of the function body.
[list_end]
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