path: root/doc/Eval.3

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.so man.macros
.TH Tcl_Eval 3 8.1 Tcl "Tcl Library Procedures"
.BS
.SH NAME
Tcl_EvalObjEx, Tcl_EvalObjv, Tcl_Eval, Tcl_EvalEx \- execute Tcl scripts
.SH SYNOPSIS
.nf
\fB#include <tcl.h>\fR
.sp
int
\fBTcl_EvalObjEx\fR(\fIinterp, objPtr, flags\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)
.SH ARGUMENTS
.AS Tcl_Interp **termPtr
.AP Tcl_Interp *interp in
Interpreter in which to execute 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 value 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.
.AP "const char" *fileName in
Name of a file containing a Tcl script.
.AP int objc in
The number of values 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 values; each value 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.
.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 value 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_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 value 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 values 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 a value 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.
.PP
\fBTcl_EvalEx\fR is an extended version of \fBTcl_Eval\fR that takes
additional arguments \fInumBytes\fR and \fIflags\fR.  \fBTcl_EvalEx\fR
is generally preferred over \fBTcl_Eval\fR.

.SH "FLAG BITS"
.PP
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 a value 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 that are active).

.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
execute, file, global, result, script, value