path: root/doc/Eval.3

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'\" Copyright (c) 1989-1993 The Regents of the University of California.
'\" Copyright (c) 1994-1997 Sun Microsystems, Inc.
'\" Copyright (c) 2000 Scriptics Corporation.
'\" Copyright (c) 2006-2008 Joe Mistachkin.
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'\" RCS: @(#) $Id: Eval.3,v 1.28 2008/06/13 05:45:07 mistachkin Exp $
'\" 
.so man.macros
.TH Tcl_Eval 3 8.6 Tcl "Tcl Library Procedures"
.BS
.SH NAME
Tcl_EvalObjEx, Tcl_EvalFile, Tcl_EvalObjv, Tcl_Eval, Tcl_EvalEx, Tcl_GlobalEval, Tcl_GlobalEvalObj, Tcl_VarEval, Tcl_VarEvalVA, Tcl_CancelEval, Tcl_Canceled \- execute and cancel Tcl scripts
.SH SYNOPSIS
.nf
\fB#include <tcl.h>\fR
.sp
int
\fBTcl_EvalObjEx\fR(\fIinterp, objPtr, flags\fR)
.sp
int
\fBTcl_EvalFile\fR(\fIinterp, fileName\fR)
.sp
int
\fBTcl_EvalObjv\fR(\fIinterp, objc, objv, flags\fR)
.sp
int
\fBTcl_Eval\fR(\fIinterp, script\fR)
.sp
int
\fBTcl_EvalEx\fR(\fIinterp, script, numBytes, flags\fR)
.sp
int
\fBTcl_GlobalEval\fR(\fIinterp, script\fR)
.sp
int
\fBTcl_GlobalEvalObj\fR(\fIinterp, objPtr\fR)
.sp
int
\fBTcl_VarEval\fR(\fIinterp, part, part, ... \fB(char *) NULL\fR)
.sp
int
\fBTcl_VarEvalVA\fR(\fIinterp, argList\fR)
.sp
int
\fBTcl_CancelEval\fR(\fIinterp, clientData, flags\fR)
.sp
int
\fBTcl_Canceled\fR(\fIinterp, flags\fR)
.SH ARGUMENTS
.AS Tcl_Interp **termPtr
.AP Tcl_Interp *interp in
Interpreter in which to execute or cancel the script.  The interpreter's
result is modified to hold the result or error message from the script.
.AP Tcl_Obj *objPtr in
A Tcl object containing the script to execute.
.AP int flags in
ORed combination of flag bits that specify additional options.
\fBTCL_EVAL_GLOBAL\fR and \fBTCL_EVAL_DIRECT\fR are currently supported.
For \fBTcl_CancelEval\fR, only \fBTCL_CANCEL_UNWIND\fR is currently
supported.  For \fBTcl_Canceled\fR, only \fBTCL_LEAVE_ERR_MSG\fR and
\fBTCL_CANCEL_UNWIND\fR are currently supported.
.AP "const char" *fileName in
Name of a file containing a Tcl script.
.AP int objc in
The number of objects in the array pointed to by \fIobjPtr\fR;
this is also the number of words in the command.
.AP 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.
.AP int numBytes in
The number of bytes in \fIscript\fR, not including any
null terminating character.  If \-1, then all characters up to the
first null byte are used.
.AP "const char" *script in
Points to first byte of script to execute (null-terminated and UTF-8).
.AP char *part in
String forming part of a Tcl script.
.AP va_list argList in
An argument list which must have been initialized using
\fBva_start\fR, and cleared using \fBva_end\fR.
.AP ClientData clientData in
Currently, reserved for future use.
It should be set to NULL.
.BE

.SH DESCRIPTION
.PP
The procedures described here are invoked to execute Tcl scripts in
various forms.
\fBTcl_EvalObjEx\fR is the core procedure and is used by many of the others.
It executes the commands in the script stored in \fIobjPtr\fR
until either an error occurs or the end of the script is reached.
If this is the first time \fIobjPtr\fR has been executed,
its commands are compiled into bytecode instructions
which are then executed.  The
bytecodes are saved in \fIobjPtr\fR so that the compilation step
can be skipped if the object is evaluated again in the future.
.PP
The return value from \fBTcl_EvalObjEx\fR (and all the other procedures
described here) is a Tcl completion code with
one of the values \fBTCL_OK\fR, \fBTCL_ERROR\fR, \fBTCL_RETURN\fR,
\fBTCL_BREAK\fR, or \fBTCL_CONTINUE\fR, or possibly some other
integer value originating in an extension.
In addition, a result value or error message is left in \fIinterp\fR's
result; it can be retrieved using \fBTcl_GetObjResult\fR.
.PP
\fBTcl_EvalFile\fR reads the file given by \fIfileName\fR and evaluates
its contents as a Tcl script.  It returns the same information as
\fBTcl_EvalObjEx\fR.
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
.QW \e32
(^Z) for all platforms. If you require a
.QW ^Z
in code for string comparison, you can use
.QW \e032
or
.QW \eu001a ,
which will be safely substituted by the Tcl interpreter into
.QW ^Z .
.PP
\fBTcl_EvalObjv\fR executes a single pre-parsed command instead of a
script.  The \fIobjc\fR and \fIobjv\fR arguments contain the values
of the words for the Tcl command, one word in each object in
\fIobjv\fR.  \fBTcl_EvalObjv\fR evaluates the command and returns
a completion code and result just like \fBTcl_EvalObjEx\fR.
The caller of \fBTcl_EvalObjv\fR has to manage the reference count of the
elements of \fIobjv\fR, insuring that the objects are valid until
\fBTcl_EvalObjv\fR returns.  
.PP
\fBTcl_Eval\fR is similar to \fBTcl_EvalObjEx\fR except that the script to
be executed 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
\fBTcl_ExternalToUtfDString\fR or \fBTcl_ExternalToUtf\fR when it is known
to possibly contain upper ASCII characters whose possible combinations
might be a UTF-8 special code.  The string is parsed and executed directly
(using \fBTcl_EvalObjv\fR) instead of compiling it and executing the
bytecodes.  In situations where it is known that the script will never be
executed again, \fBTcl_Eval\fR may be faster than \fBTcl_EvalObjEx\fR.
 \fBTcl_Eval\fR returns a completion code and result just like 
\fBTcl_EvalObjEx\fR.  Note: for backward compatibility with versions before
Tcl 8.0, \fBTcl_Eval\fR copies the object result in \fIinterp\fR to
\fIinterp->result\fR (use is deprecated) where it can be accessed directly.
 This makes \fBTcl_Eval\fR somewhat slower than \fBTcl_EvalEx\fR, which
does not do the copy.
.PP
\fBTcl_EvalEx\fR is an extended version of \fBTcl_Eval\fR that takes
additional arguments \fInumBytes\fR and \fIflags\fR.  For the
efficiency reason given above, \fBTcl_EvalEx\fR is generally preferred
over \fBTcl_Eval\fR.
.PP
\fBTcl_GlobalEval\fR and \fBTcl_GlobalEvalObj\fR are older procedures
that are now deprecated.  They are similar to \fBTcl_EvalEx\fR and
\fBTcl_EvalObjEx\fR except that the script is evaluated in the global
namespace and its variable context consists of global variables only
(it ignores any Tcl procedures that are active).  These functions are
equivalent to using the \fBTCL_EVAL_GLOBAL\fR flag (see below).
.PP
\fBTcl_VarEval\fR takes any number of string arguments
of any length, concatenates them into a single string,
then calls \fBTcl_Eval\fR to execute that string as a Tcl command.
It returns the result of the command and also modifies
\fIinterp->result\fR in the same way as \fBTcl_Eval\fR.
The last argument to \fBTcl_VarEval\fR must be NULL to indicate the end
of arguments.  \fBTcl_VarEval\fR is now deprecated.
.PP
\fBTcl_VarEvalVA\fR is the same as \fBTcl_VarEval\fR except that
instead of taking a variable number of arguments it takes an argument
list. Like \fBTcl_VarEval\fR, \fBTcl_VarEvalVA\fR is deprecated.
.PP
\fBTcl_CancelEval\fR cancels or unwinds the script in progress soon after
the next invocation of asynchronous handlers, causing \fBTCL_ERROR\fR to be
the return code for that script.  This function is thread-safe and may be
called from any thread in the process.
.PP
\fBTcl_Canceled\fR checks if the script in progress has been canceled and
returns \fBTCL_ERROR\fR if it has.  Otherwise, \fBTCL_OK\fR is returned.
Extensions 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.

.SH "FLAG BITS"
Any ORed combination of the following values may be used for the
\fIflags\fR argument to procedures such as \fBTcl_EvalObjEx\fR:
.TP 23
\fBTCL_EVAL_DIRECT\fR
This flag is only used by \fBTcl_EvalObjEx\fR; 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 \fBTcl_EvalEx\fR.  The
\fBTCL_EVAL_DIRECT\fR flag is useful in situations where the
contents of an object are going to change immediately, so the
bytecodes will not be reused in a future execution.  In this case,
it is faster to execute the script directly.
.TP 23
\fBTCL_EVAL_GLOBAL\fR
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).
.TP 23
\fBTCL_CANCEL_UNWIND\fR
This flag is only used by \fBTcl_CancelEval\fR and \fBTcl_Canceled\fR;
it is ignored by other procedures.  For \fBTcl_CancelEval\fR, if this
flag is set, the script in progress is canceled and the evaluation
stack for the interpreter is unwound.  For \fBTcl_Canceled\fR, 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.
.TP 23
\fBTCL_LEAVE_ERR_MSG\fR
This flag is only used by \fBTcl_Canceled\fR; it is ignored by
other procedures.  If an error is returned and this bit is set in
\fIflags\fR, then an error message will be left in the interpreter's
result, where it can be retrieved with \fBTcl_GetObjResult\fR or
\fBTcl_GetStringResult\fR.  If this flag bit is not set then no error
message is left and the interpreter's result will not be modified.

.SH "MISCELLANEOUS DETAILS"
.PP
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 \fBTCL_OK\fR is returned
from a nested \fBTcl_EvalObjEx\fR 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 \fBfor\fR, will check for certain
return codes, like \fBTCL_BREAK\fR and \fBTCL_CONTINUE\fR, and process them
specially without returning.
.PP
\fBTcl_EvalObjEx\fR keeps track of how many nested \fBTcl_EvalObjEx\fR
invocations are in progress for \fIinterp\fR.
If a code of \fBTCL_RETURN\fR, \fBTCL_BREAK\fR, or \fBTCL_CONTINUE\fR is
about to be returned from the topmost \fBTcl_EvalObjEx\fR
invocation for \fIinterp\fR,
it converts the return code to \fBTCL_ERROR\fR
and sets \fIinterp\fR's result to an error message indicating that
the \fBreturn\fR, \fBbreak\fR, or \fBcontinue\fR command was
invoked in an inappropriate place.
This means that top-level applications should never see a return code
from \fBTcl_EvalObjEx\fR other then \fBTCL_OK\fR or \fBTCL_ERROR\fR.

.SH KEYWORDS
cancel, execute, file, global, object, result, script, unwind