Tcl7.6 C API Man Page -- Eval (n)
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Tcl_Eval, Tcl_VarEval, Tcl_EvalFile, Tcl_GlobalEval - execute Tcl commands


#include <tcl.h>

Tcl_Eval(interp, cmd)

Tcl_VarEval(interp, string, string, ... (char *) NULL)

Tcl_EvalFile(interp, fileName)

Tcl_GlobalEval(interp, cmd)


Tcl_Interp *interp (in) Interpreter in which to execute the command. String result will be stored in interp>result.

*cmd (in) Command (or sequence of commands) to execute. Must be in writable memory (Tcl_Eval makes temporary modifications to the command).

*string (in) String forming part of Tcl command.

*fileName (in) Name of file containing Tcl command string.


All four of these procedures execute Tcl commands. Tcl_Eval is the core procedure: it parses commands from cmd and executes them in order until either an error occurs or it reaches the end of the string. 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 (result value or error message). 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.

Tcl_GlobalEval is similar to Tcl_Eval except that it processes the command at global level. This means that the variable context for the command consists of global variables only (it ignores any Tcl procedure that is active). This produces an effect similar to the Tcl command ``uplevel 0''.

During the processing of a Tcl command it is legal to make nested calls to evaluate other commands (this is how conditionals, loops, and procedures 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, then Tcl_Eval 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.


command, execute, file, global, interpreter, variable

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