Tcl_Eval(3) Tcl (7.0) Tcl_Eval(3)
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NAME
Tcl_Eval, Tcl_VarEval, Tcl_EvalFile, Tcl_GlobalEval -
execute Tcl commands
SYNOPSIS
#include <tcl.h>
int
Tcl_Eval(interp, cmd)
int
Tcl_VarEval(interp, string, string, ... (char *) NULL)
int
Tcl_EvalFile(interp, fileName)
int
Tcl_GlobalEval(interp, cmd)
ARGUMENTS
Tcl_Interp *interp (in) Interpreter in which to
execute the command. A
string result will be
stored in interp-
>result.
char *cmd (in) Command (or sequence of
commands) to execute.
Must be in writable
memory (Tcl_Eval makes
temporary modifications
to the command).
char *string (in) String forming part of
Tcl command.
char *fileName (in) Name of file containing
Tcl command string.
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DESCRIPTION
All four of these procedures execute Tcl commands. Tcl_Eval
is the core procedure and is used by all the others. It
executes the commands in the script held by cmd until either
an error occurs or it reaches the end of the script.
Note that Tcl_Eval and Tcl_GlobalEval have been largely
replaced by the object-based procedures Tcl_EvalObj and
Tcl_GlobalEvalObj. Those object-based procedures evaluate a
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Tcl_Eval(3) Tcl (7.0) Tcl_Eval(3)
script held in a Tcl object instead of a string. The object
argument can retain the bytecode instructions for the script
and so avoid reparsing the script each time it is executed.
Tcl_Eval is implemented using Tcl_EvalObj but is slower
because it must reparse the script each time since there is
no object to retain the bytecode instructions.
The return value from Tcl_Eval is one of the Tcl return
codes TCL_OK, TCL_ERROR, TCL_RETURN, TCL_BREAK, or
TCL_CONTINUE, and interp->result will point to a string with
additional information (a result value or error message).
If an error occurs during compilation, this return
information describes the error. Otherwise, this return
information corresponds to the last command executed from
cmd.
Tcl_VarEval takes any number of string arguments of any
length, concatenates 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 usual fashion for Tcl commands. The last
argument to Tcl_VarEval must be NULL to indicate the end of
arguments.
Tcl_EvalFile reads the file given by fileName and evaluates
its contents as a Tcl command by calling Tcl_Eval. It
returns a standard Tcl result that reflects the result of
evaluating the file. If the file couldn't be read then a
Tcl error is returned to describe why the file couldn't be
read.
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_Eval
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_Eval keeps track of how many nested Tcl_Eval 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_Eval invocation for interp, it converts the
return code to TCL_ERROR and sets interp->result to point 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_Eval other then TCL_OK or TCL_ERROR.
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Tcl_Eval(3) Tcl (7.0) Tcl_Eval(3)
SEE ALSO
Tcl_EvalObj, Tcl_GlobalEvalObj
KEYWORDS
command, execute, file, global, object, object result,
variable
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