Tcl_Eval(3) Tcl Library Procedures Tcl_Eval(3)

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NAME

Tcl_EvalObjEx, Tcl_EvalFile, Tcl_EvalObjv, Tcl_Eval, Tcl_EvalEx,
Tcl_GlobalEval, Tcl_GlobalEvalObj, Tcl_VarEval, Tcl_VarEvalVA -
execute 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)

ARGUMENTS

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.

Tcl_Obj *objPtr (in) A Tcl value containing the script
to execute.

int flags (in) OR'ed combination of flag bits
that specify additional options.
TCL_EVAL_GLOBAL and
TCL_EVAL_DIRECT are currently
supported.

const char *fileName (in) Name of a file containing a Tcl
script.

int objc (in) The number of values in the array
pointed to by objv; this is also
the number of words in the
command.

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.

int numBytes (in) The number of bytes in script, not
including any null terminating
character. 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).

const 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.
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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 compiled into bytecode instructions which are then
executed. The bytecodes are saved in objPtr so that the compilation
step can be skipped if the value 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
contents as a Tcl script. It returns the same information as
Tcl_EvalObjEx. 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 substituted by the Tcl interpreter into "^Z".

Tcl_EvalObjv executes a single preparsed command instead of a script.
The objc and objv arguments contain the values of the words for the
Tcl command, one word in each value in objv. Tcl_EvalObjv evaluates
the command and returns a completion code and result just like
Tcl_EvalObjEx. The caller of Tcl_EvalObjv has to manage the
reference count of the elements of objv, insuring that the values are
valid until Tcl_EvalObjv returns.

Tcl_Eval is similar to Tcl_EvalObjEx 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 Tcl_ExternalToUtfDString or Tcl_ExternalToUtf 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 Tcl_EvalObjv) instead of compiling it and
executing the bytecodes. 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 value result in interp to interp->result
(use is deprecated) 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 procedures 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,
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 same way as Tcl_Eval.
The last argument to Tcl_VarEval must be (char *)NULL to indicate the
end of arguments.

Tcl_VarEvalVA is the same as Tcl_VarEval except that instead of
taking a variable number of arguments it takes an argument list.
Tcl_VarEvalVA is now deprecated.

FLAG BITS

Any OR'ed 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 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.

TCL_EVAL_GLOBAL If this flag is set, the script is evaluated
in the global namespace instead of the current
namespace and its variable context consists of
global variables only (it ignores any Tcl
procedures that are active).

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 than TCL_OK or
TCL_ERROR.

KEYWORDS

execute, file, global, result, script, value

Tcl 8.1 Tcl_Eval(3)