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Tcl Library Procedures

NAME

SYNOPSIS

ARGUMENTS

Tcl_Interp *interp (in)

Interpreter in which to create new command.

char *cmdName (in)

Name of command to create or delete.

Tcl_CmdProc *proc (in)

Implementation of new command: proc will be called whenever cmdName is invoked as a command.

ClientData clientData (in)

Arbitrary one-word value to pass to proc and deleteProc.

Tcl_CmdDeleteProc *deleteProc (in)

Procedure to call before cmdName is deleted from the interpreter; allows for command-specific cleanup. If NULL, then no procedure is called before the command is deleted.

DESCRIPTION

Tcl_CreateCommand defines a new command in interp and associates it with procedure proc such that whenever cmdName is invoked as a Tcl command (via a call to Tcl_Eval) the Tcl interpreter will call proc to process the command. If there is already a command cmdName associated with the interpreter, it is deleted. Proc should have arguments and result that match the type Tcl_CmdProc: typedef int Tcl_CmdProc(
ClientData clientData,
Tcl_Interp *interp,
int argc,
char *argv[]);
When proc is invoked the clientData and interp parameters will be copies of the clientData and interp arguments given to Tcl_CreateCommand. Typically, clientData points to an application-specific data structure that describes what to do when the command procedure is invoked. Argc and argv describe the arguments to the command, argc giving the number of arguments (including the command name) and argv giving the values of the arguments as strings. The argv array will contain argc+1 values; the first argc values point to the argument strings, and the last value is NULL.

Proc must return an integer code that is either TCL_OK, TCL_ERROR, TCL_RETURN, TCL_BREAK, or TCL_CONTINUE. See the Tcl overview man page for details on what these codes mean. Most normal commands will only return TCL_OK or TCL_ERROR. In addition, proc must set interp->result to point to a string value; in the case of a TCL_OK return code this gives the result of the command, and in the case of TCL_ERROR it gives an error message. The Tcl_SetResult procedure provides an easy interface for setting the return value; for complete details on how the interp->result field is managed, see the Tcl_Interp man page. Before invoking a command procedure, Tcl_Eval sets interp->result to point to an empty string, so simple commands can return an empty result by doing nothing at all.

The contents of the argv array are copies made by the Tcl interpreter for the use of proc. Proc may alter any of the strings in argv. However, the argv array is recycled as soon as proc returns, so proc must not set interp->result to point anywhere within the argv values (call Tcl_SetResult with status TCL_VOLATILE if you want to return something from the argv array).

DeleteProc will be invoked when (if) cmdName is deleted. This can occur through a call to Tcl_DeleteCommand or Tcl_DeleteInterp, or by replacing cmdName in another call to Tcl_CreateCommand. DeleteProc is invoked before the command is deleted, and gives the application an opportunity to release any structures associated with the command. DeleteProc should have arguments and result that match the type Tcl_CmdDeleteProc:
typedef void Tcl_CmdDeleteProc(ClientData clientData);

The clientData argument will be the same as the clientData argument passed to Tcl_CreateCommand.

Tcl_DeleteCommand deletes a command from a command interpreter. Once the call completes, attempts to invoke cmdName in interp will result in errors. If cmdName isn't bound as a command in interp then Tcl_DeleteCommand does nothing and returns -1; otherwise it returns 0. There are no restrictions on cmdName: it may refer to a built-in command, an application-specific command, or a Tcl procedure.

KEYWORDS

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Copyright © 1994-1996 Sun Microsystems, Inc.