Tcl_Eval manual page - Tcl Library Procedures

#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): ORed 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 objPtr; 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.

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 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 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 the interpreter 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.

Tcl_VarEvalVA is the same as Tcl_VarEval except that instead of taking a variable number of arguments it takes an argument list. Interfaces using argument lists have been found to be nonportable in practice. This function is deprecated and will be removed in Tcl 9.0.

FLAG BITS

Any ORed 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.

REFERENCE COUNT MANAGEMENT

Tcl_EvalObjEx and Tcl_GlobalEvalObj both increment and decrement the reference count of their objPtr argument; you must not pass them any value with a reference count of zero. They also manipulate the interpreter result; you must not count on the interpreter result to hold the reference count of any value over these calls.

Tcl_EvalObjv may increment and decrement the reference count of any value passed via its objv argument; you must not pass any value with a reference count of zero. This function also manipulates the interpreter result; you must not count on the interpreter result to hold the reference count of any value over this call.

KEYWORDS

execute, file, global, result, script, value