Tcl_Eval(3) Tcl Library Procedures Tcl_Eval(3)______________________________________________________________________________NAME
Tcl_EvalObjEx, Tcl_EvalFile, Tcl_EvalObjv, Tcl_Eval, Tcl_EvalEx,
Tcl_GlobalEval, Tcl_GlobalEvalObj, Tcl_VarEval, Tcl_VarEvalVA, Tcl_Can‐
celEval, Tcl_Canceled - execute and cancel Tcl scripts
SYNOPSIS
#include <tcl.h>
int
Tcl_EvalObjEx(interp, objPtr, flags)
int
Tcl_EvalFile(interp, fileName)
int
Tcl_EvalObjv(interp, objc, objv, flags)
int
Tcl_Eval(interp, script)
int
Tcl_EvalEx(interp, script, numBytes, flags)
int
Tcl_GlobalEval(interp, script)
int
Tcl_GlobalEvalObj(interp, objPtr)
int
Tcl_VarEval(interp, part, part, ... (char *) NULL)
int
Tcl_VarEvalVA(interp, argList)
int
Tcl_CancelEval(interp, clientData, flags)
int
Tcl_Canceled(interp, flags)
ARGUMENTS
Tcl_Interp *interp (in) Interpreter in which to execute or
cancel the script. The inter‐
preter's result is modified to hold
the result or error message from the
script.
Tcl_Obj *objPtr (in) A Tcl object containing the script
to execute.
int flags (in) ORed combination of flag bits that
specify additional options.
TCL_EVAL_GLOBAL and TCL_EVAL_DIRECT
are currently supported. For
Tcl_CancelEval, only TCL_CAN‐
CEL_UNWIND is currently supported.
For Tcl_Canceled, only
TCL_LEAVE_ERR_MSG and TCL_CAN‐
CEL_UNWIND are currently supported.
const char *fileName (in) Name of a file containing a Tcl
script.
int objc (in) The number of objects in the array
pointed to by objPtr; this is also
the number of words in the command.
Tcl_Obj **objv (in) Points to an array of pointers to
objects; each object holds the value
of a single word in the command to
execute.
int numBytes (in) The number of bytes in script, not
including any null terminating char‐
acter. If -1, then all characters
up to the first null byte are used.
const char *script (in) Points to first byte of script to
execute (null-terminated and UTF-8).
char *part (in) String forming part of a Tcl script.
va_list argList (in) An argument list which must have
been initialized using va_start, and
cleared using va_end.
ClientData clientData (in) Currently, reserved for future use.
It should be set to NULL.
_________________________________________________________________DESCRIPTION
The procedures described here are invoked to execute Tcl scripts in
various forms. Tcl_EvalObjEx is the core procedure and is used by many
of the others. It executes the commands in the script stored in objPtr
until either an error occurs or the end of the script is reached. If
this is the first time objPtr has been executed, its commands are com‐
piled into bytecode instructions which are then executed. The byte‐
codes are saved in objPtr so that the compilation step can be skipped
if the object is evaluated again in the future.
The return value from Tcl_EvalObjEx (and all the other procedures
described here) is a Tcl completion code with one of the values TCL_OK,
TCL_ERROR, TCL_RETURN, TCL_BREAK, or TCL_CONTINUE, or possibly some
other integer value originating in an extension. In addition, a result
value or error message is left in interp's result; it can be retrieved
using Tcl_GetObjResult.
Tcl_EvalFile reads the file given by fileName and evaluates its con‐
tents as a Tcl script. It returns the same information as Tcl_EvalOb‐
jEx. If the file could not be read then a Tcl error is returned to
describe why the file could not be read. The eofchar for files is
“\32” (^Z) for all platforms. If you require a “^Z” in code for string
comparison, you can use “\032” or “\u001a”, which will be safely sub‐
stituted by the Tcl interpreter into “^Z”.
Tcl_EvalObjv executes a single pre-parsed command instead of a script.
The objc and objv arguments contain the values of the words for the Tcl
command, one word in each object in objv. Tcl_EvalObjv evaluates the
command and returns a completion code and result just like Tcl_EvalOb‐
jEx. The caller of Tcl_EvalObjv has to manage the reference count of
the elements of objv, insuring that the objects are valid until
Tcl_EvalObjv returns.
Tcl_Eval is similar to Tcl_EvalObjEx except that the script to be exe‐
cuted is supplied as a string instead of an object and no compilation
occurs. The string should be a proper UTF-8 string as converted by
Tcl_ExternalToUtfDString or Tcl_ExternalToUtf when it is known to pos‐
sibly contain upper ASCII characters whose possible combinations might
be a UTF-8 special code. The string is parsed and executed directly
(using Tcl_EvalObjv) instead of compiling it and executing the byte‐
codes. In situations where it is known that the script will never be
executed again, Tcl_Eval may be faster than Tcl_EvalObjEx.
Tcl_Eval returns a completion code and result just like Tcl_EvalObjEx.
Note: for backward compatibility with versions before Tcl 8.0, Tcl_Eval
copies the object result in interp to interp->result (use is depre‐
cated) where it can be accessed directly.
This makes Tcl_Eval somewhat slower than Tcl_EvalEx, which does not do
the copy.
Tcl_EvalEx is an extended version of Tcl_Eval that takes additional
arguments numBytes and flags. For the efficiency reason given above,
Tcl_EvalEx is generally preferred over Tcl_Eval.
Tcl_GlobalEval and Tcl_GlobalEvalObj are older procedures that are now
deprecated. They are similar to Tcl_EvalEx and Tcl_EvalObjEx except
that the script is evaluated in the global namespace and its variable
context consists of global variables only (it ignores any Tcl proce‐
dures that are active). These functions are equivalent to using the
TCL_EVAL_GLOBAL flag (see below).
Tcl_VarEval takes any number of string arguments of any length, con‐
catenates them into a single string, then calls Tcl_Eval to execute
that string as a Tcl command. It returns the result of the command and
also modifies interp->result in the same way as Tcl_Eval. The last
argument to Tcl_VarEval must be NULL to indicate the end of arguments.
Tcl_VarEval is now deprecated.
Tcl_VarEvalVA is the same as Tcl_VarEval except that instead of taking
a variable number of arguments it takes an argument list. Like
Tcl_VarEval, Tcl_VarEvalVA is deprecated.
Tcl_CancelEval cancels or unwinds the script in progress soon after the
next invocation of asynchronous handlers, causing TCL_ERROR to be the
return code for that script. This function is thread-safe and may be
called from any thread in the process.
Tcl_Canceled checks if the script in progress has been canceled and
returns TCL_ERROR if it has. Otherwise, TCL_OK is returned. Exten‐
sions can use this function to check to see if they should abort a long
running command. This function is thread sensitive and may only be
called from the thread the interpreter was created in.
FLAG BITS
Any ORed combination of the following values may be used for the flags
argument to procedures such as Tcl_EvalObjEx:
TCL_EVAL_DIRECT This flag is only used by Tcl_EvalObjEx; it is
ignored by other procedures. If this flag bit
is set, the script is not compiled to bytecodes;
instead it is executed directly as is done by
Tcl_EvalEx. The TCL_EVAL_DIRECT flag is useful
in situations where the contents of an object
are going to change immediately, so the byte‐
codes will not be reused in a future execution.
In this case, it is faster to execute the script
directly.
TCL_EVAL_GLOBAL If this flag is set, the script is processed at
global level. This means that it is evaluated
in the global namespace and its variable context
consists of global variables only (it ignores
any Tcl procedures at are active).
TCL_CANCEL_UNWIND This flag is only used by Tcl_CancelEval and
Tcl_Canceled; it is ignored by other procedures.
For Tcl_CancelEval, if this flag is set, the
script in progress is canceled and the evalua‐
tion stack for the interpreter is unwound. For
Tcl_Canceled, if this flag is set, the script in
progress is considered to be canceled only if
the evaluation stack for the interpreter is
being unwound.
TCL_LEAVE_ERR_MSG This flag is only used by Tcl_Canceled; it is
ignored by other procedures. If an error is
returned and this bit is set in flags, then an
error message will be left in the interpreter's
result, where it can be retrieved with Tcl_GetO‐
bjResult or Tcl_GetStringResult. If this flag
bit is not set then no error message is left and
the interpreter's result will not be modified.
MISCELLANEOUS DETAILS
During the processing of a Tcl command it is legal to make nested calls
to evaluate other commands (this is how procedures and some control
structures are implemented). If a code other than TCL_OK is returned
from a nested Tcl_EvalObjEx invocation, then the caller should normally
return immediately, passing that same return code back to its caller,
and so on until the top-level application is reached. A few commands,
like for, will check for certain return codes, like TCL_BREAK and
TCL_CONTINUE, and process them specially without returning.
Tcl_EvalObjEx keeps track of how many nested Tcl_EvalObjEx invocations
are in progress for interp. If a code of TCL_RETURN, TCL_BREAK, or
TCL_CONTINUE is about to be returned from the topmost Tcl_EvalObjEx
invocation for interp, it converts the return code to TCL_ERROR and
sets interp's result to an error message indicating that the return,
break, or continue command was invoked in an inappropriate place. This
means that top-level applications should never see a return code from
Tcl_EvalObjEx other then TCL_OK or TCL_ERROR.
KEYWORDS
cancel, execute, file, global, object, result, script, unwind
Tcl 8.6 Tcl_Eval(3)
