Tcl Library Procedures - Tcl

NAME

Tcl_EvalObj, Tcl_EvalFile, Tcl_EvalObjv, Tcl_Eval, Tcl_Eval2, Tcl_GlobalEval, Tcl_VarEval - execute Tcl scripts

SYNOPSIS

ARGUMENTS

DESCRIPTION

FLAG BITS

TCL_EVAL_DIRECT

TCL_EVAL_GLOBAL

MISCELLANEOUS DETAILS

KEYWORDS

NAME

Tcl_EvalObj, Tcl_EvalFile, Tcl_EvalObjv, Tcl_Eval, Tcl_Eval2, Tcl_GlobalEval, Tcl_VarEval - execute Tcl scripts

#include <tcl.h>
int
Tcl_EvalObj(interp, objPtr, flags)
int
Tcl_EvalFile(interp, fileName)
int
Tcl_EvalObjv(interp, objc, objv, command, numBytes, flags)
int
Tcl_Eval(interp, script)
int
Tcl_Eval2(interp, script, numBytes, flags)
int
Tcl_GlobalEval(interp, script)
int
Tcl_VarEval(interp, string, string, ... (char *) NULL)

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 object containing the script to execute.
int flags (in): ORed combination of flag bits that specify additional options. TCL_EVAL_GLOBAL and TCL_EVAL_DIRECT are currently supported.
char *fileName (in): Name of a file containing a Tcl script.
int *objc (in): The number of objects in the array pointed to by objPtr; this is also the number of words in the command.
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.
char *command (in): Points to the beginning of the string representation of the command, if there is one. If the string representation of the command is unknown then an empty string should be supplied. This information is used for command tracing.
int numBytes (in): The number of bytes in command or script, not including any null terminating character. If -1, then all characters up to the first null byte are used.
char *script (in): Points to first byte of script to execute. This script must be in writable memory: temporary modifications are made to it during parsing.
char *string (in): String forming part of a Tcl script.

DESCRIPTION

The procedures described here are invoked to execute Tcl scripts in various forms. Tcl_EvalObj 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 object is evaluated again in the future.

The return value from Tcl_EvalObj (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. 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_EvalObj. If the file couldn't be read then a Tcl error is returned to describe why the file couldn't be read.

Tcl_EvalObjv executes a single pre-parsed command instead of a script. The objc and objv arguments contain the values of the words for the Tcl command, one word in each object in objv. Tcl_EvalObjv evaluates the command and returns a completion code and result just like Tcl_EvalObj. The command argument is used only to provide contextual information to command traces. Note: unlike the other procedures described here, Tcl_EvalObjv does not add any information to the errorInfo variable after an error. It is up to the caller to do this, if it wishes.

Tcl_Eval is similar to Tcl_EvalObj except that the script to be executed is supplied as a string instead of an object and no compilation occurs. 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_EvalObj. Tcl_Eval returns a completion code and result just like Tcl_EvalObj. Note: for backward compatibility with versions before Tcl 8.0, Tcl_Eval copies the object result in interp to interp->result where it can be accessed directly. This makes Tcl_Eval somewhat slower than Tcl_Eval2, which doesn't do the copy.

Tcl_Eval2 is an extended version of Tcl_Eval that takes additional arguments numBytes and flags. For the efficiency reason given above, Tcl_Eval2 is generally preferred over Tcl_Eval.

Tcl_GlobalEval is an older procedure that is now deprecated. It is similar to Tcl_Eval 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). Like Tcl_Eval, it leaves a null-terminated string version of the result in interp->result where it can be accessed directly.

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 NULL to indicate the end of arguments. Tcl_VarEval is now deprecated.

FLAG BITS

Any ORed combination of the following values may be used for the flags argument to procedures such as Tcl_EvalObj:

TCL_EVAL_DIRECT: This flag is only used by Tcl_EvalObj; 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_Eval2. The TCL_EVAL_DIRECT flag is useful in situations where the contents of an object are going to change immediately, so the bytecodes won't be reused in a future execution. In this case, it's faster to execute the script directly.
TCL_EVAL_GLOBAL: 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).

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_EvalObj 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_EvalObj keeps track of how many nested Tcl_EvalObj 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_EvalObj 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_EvalObj other then TCL_OK or TCL_ERROR.

KEYWORDS

execute, file, global, object, result, script

Copyright © 1989-1993 The Regents of the University of California.
Copyright © 1994-1997 Sun Microsystems, Inc.
Copyright © 1995-1997 Roger E. Critchlow Jr.