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markom |
'\"
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'\" Copyright (c) 1989-1993 The Regents of the University of California.
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'\" Copyright (c) 1994-1997 Sun Microsystems, Inc.
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'\"
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'\" See the file "license.terms" for information on usage and redistribution
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'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
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'\"
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'\" RCS: @(#) $Id: Eval.3,v 1.1.1.1 2002-01-16 10:25:23 markom Exp $
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'\"
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.so man.macros
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.TH Tcl_Eval 3 7.0 Tcl "Tcl Library Procedures"
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.BS
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.SH NAME
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Tcl_Eval, Tcl_VarEval, Tcl_EvalFile, Tcl_GlobalEval \- execute Tcl commands
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.SH SYNOPSIS
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.nf
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\fB#include \fR
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.sp
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int
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\fBTcl_Eval\fR(\fIinterp, cmd\fR)
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.sp
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int
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\fBTcl_VarEval\fR(\fIinterp, string, string, ... \fB(char *) NULL\fR)
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.sp
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int
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\fBTcl_EvalFile\fR(\fIinterp, fileName\fR)
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.sp
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int
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\fBTcl_GlobalEval\fR(\fIinterp, cmd\fR)
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.SH ARGUMENTS
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.AS Tcl_Interp **termPtr;
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.AP Tcl_Interp *interp in
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Interpreter in which to execute the command.
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A string result will be stored in \fIinterp->result\fR.
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.AP char *cmd in
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Command (or sequence of commands) to execute. Must be in writable
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memory (\fBTcl_Eval\fR makes temporary modifications to the command).
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.AP char *string in
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String forming part of Tcl command.
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.AP char *fileName in
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Name of file containing Tcl command string.
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.BE
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.SH DESCRIPTION
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.PP
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All four of these procedures execute Tcl commands.
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\fBTcl_Eval\fR is the core procedure and is used by all the others.
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It executes the commands in the script held by \fIcmd\fR
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until either an error occurs or it reaches the end of the script.
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.PP
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Note that \fBTcl_Eval\fR and \fBTcl_GlobalEval\fR
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have been largely replaced by the
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object-based procedures \fBTcl_EvalObj\fR and \fBTcl_GlobalEvalObj\fR.
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Those object-based procedures evaluate a script held in a Tcl object
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instead of a string.
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The object argument can retain the bytecode instructions for the script
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and so avoid reparsing the script each time it is executed.
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\fBTcl_Eval\fR is implemented using \fBTcl_EvalObj\fR
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but is slower because it must reparse the script each time
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since there is no object to retain the bytecode instructions.
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.PP
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The return value from \fBTcl_Eval\fR is one of the Tcl return codes
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\fBTCL_OK\fR, \fBTCL_ERROR\fR, \fBTCL_RETURN\fR, \fBTCL_BREAK\fR, or
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\fBTCL_CONTINUE\fR, and \fIinterp->result\fR will point to
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a string with additional information (a result value or error message).
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If an error occurs during compilation, this return information
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describes the error.
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Otherwise, this return information corresponds to the last command
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executed from \fIcmd\fR.
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.PP
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\fBTcl_VarEval\fR takes any number of string arguments
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of any length, concatenates them into a single string,
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then calls \fBTcl_Eval\fR to execute that string as a Tcl command.
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It returns the result of the command and also modifies
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\fIinterp->result\fR in the usual fashion for Tcl commands.
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The last argument to \fBTcl_VarEval\fR must be NULL to indicate the end
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of arguments.
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.PP
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\fBTcl_EvalFile\fR reads the file given by \fIfileName\fR and evaluates
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its contents as a Tcl command by calling \fBTcl_Eval\fR. It returns
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a standard Tcl result that reflects the result of evaluating the file.
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If the file couldn't be read then a Tcl error is returned to describe
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why the file couldn't be read.
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.PP
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During the processing of a Tcl command it is legal to make nested
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calls to evaluate other commands (this is how procedures and
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some control structures are implemented).
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If a code other than \fBTCL_OK\fR is returned
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from a nested \fBTcl_Eval\fR invocation,
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then the caller should normally return immediately,
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passing that same return code back to its caller,
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and so on until the top-level application is reached.
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A few commands, like \fBfor\fR, will check for certain
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return codes, like \fBTCL_BREAK\fR and \fBTCL_CONTINUE\fR, and process them
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specially without returning.
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.PP
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\fBTcl_Eval\fR keeps track of how many nested \fBTcl_Eval\fR
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invocations are in progress for \fIinterp\fR.
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If a code of \fBTCL_RETURN\fR, \fBTCL_BREAK\fR, or \fBTCL_CONTINUE\fR is
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about to be returned from the topmost \fBTcl_Eval\fR
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invocation for \fIinterp\fR,
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it converts the return code to \fBTCL_ERROR\fR
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and sets \fIinterp->result\fR
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to point to an error message indicating that
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the \fBreturn\fR, \fBbreak\fR, or \fBcontinue\fR command was
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invoked in an inappropriate place.
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This means that top-level applications should never see a return code
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from \fBTcl_Eval\fR other then \fBTCL_OK\fR or \fBTCL_ERROR\fR.
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.SH "SEE ALSO"
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Tcl_EvalObj, Tcl_GlobalEvalObj
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.SH KEYWORDS
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command, execute, file, global, object, object result, variable
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