path: root/doc/CrtCommand.3

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.TH Tcl_CreateCommand 3 "" Tcl "Tcl Library Procedures"
.so man.macros
.BS
.SH NAME
Tcl_CreateCommand \- implement new commands in C
.SH SYNOPSIS
.nf
\fB#include <tcl.h>\fR
.sp
Tcl_Command
\fBTcl_CreateCommand\fR(\fIinterp, cmdName, proc, clientData, deleteProc\fR)
.SH ARGUMENTS
.AS Tcl_CmdDeleteProc *deleteProc
.AP Tcl_Interp *interp in
Interpreter in which to create new command.
.AP "const char" *cmdName in
Name of command.
.AP Tcl_CmdProc *proc in
Implementation of new command:  \fIproc\fR will be called whenever
\fIcmdName\fR is invoked as a command.
.AP ClientData clientData in
Arbitrary one-word value to pass to \fIproc\fR and \fIdeleteProc\fR.
.AP Tcl_CmdDeleteProc *deleteProc in
Procedure to call before \fIcmdName\fR is deleted from the interpreter;
allows for command-specific cleanup.  If NULL, then no procedure is
called before the command is deleted.
.BE
.SH DESCRIPTION
.PP
\fBTcl_CreateCommand\fR defines a new command in \fIinterp\fR and associates
it with procedure \fIproc\fR such that whenever \fIcmdName\fR is
invoked as a Tcl command (via a call to \fBTcl_Eval\fR) the Tcl interpreter
will call \fIproc\fR to process the command.
It differs from \fBTcl_CreateObjCommand\fR in that a new string-based
command is defined;
that is, a command procedure is defined that takes an array of
argument strings instead of values.
The value-based command procedures registered by \fBTcl_CreateObjCommand\fR
can execute significantly faster than the string-based command procedures
defined by \fBTcl_CreateCommand\fR.
This is because they take Tcl values as arguments
and those values can retain an internal representation that
can be manipulated more efficiently.
Also, Tcl's interpreter now uses values internally.
In order to invoke a string-based command procedure
registered by \fBTcl_CreateCommand\fR,
it must generate and fetch a string representation
from each argument value before the call.
New commands should be defined using \fBTcl_CreateObjCommand\fR.
We support \fBTcl_CreateCommand\fR for backwards compatibility.
.PP
The procedures \fBTcl_DeleteCommand\fR, \fBTcl_GetCommandInfo\fR,
and \fBTcl_SetCommandInfo\fR are used in conjunction with
\fBTcl_CreateCommand\fR.
.PP
\fBTcl_CreateCommand\fR will delete an existing command \fIcmdName\fR,
if one is already associated with the interpreter.
It returns a token that may be used to refer
to the command in subsequent calls to \fBTcl_GetCommandName\fR.
If \fIcmdName\fR contains any \fB::\fR namespace qualifiers,
then the command is added to the specified namespace;
otherwise the command is added to the global namespace.
If \fBTcl_CreateCommand\fR is called for an interpreter that is in
the process of being deleted, then it does not create a new command
and it returns NULL.
\fIProc\fR should have arguments and result that match the type
\fBTcl_CmdProc\fR:
.PP
.CS
typedef int \fBTcl_CmdProc\fR(
        ClientData \fIclientData\fR,
        Tcl_Interp *\fIinterp\fR,
        int \fIargc\fR,
        const char *\fIargv\fR[]);
.CE
.PP
When \fIproc\fR is invoked the \fIclientData\fR and \fIinterp\fR
parameters will be copies of the \fIclientData\fR and \fIinterp\fR
arguments given to \fBTcl_CreateCommand\fR.
Typically, \fIclientData\fR points to an application-specific
data structure that describes what to do when the command procedure
is invoked.  \fIArgc\fR and \fIargv\fR describe the arguments to
the command, \fIargc\fR giving the number of arguments (including
the command name) and \fIargv\fR giving the values of the arguments
as strings.  The \fIargv\fR array will contain \fIargc\fR+1 values;
the first \fIargc\fR values point to the argument strings, and the
last value is NULL.  
Note that the argument strings should not be modified as they may
point to constant strings or may be shared with other parts of the
interpreter.
.PP
Note that the argument strings are encoded in normalized UTF-8 since
version 8.1 of Tcl.
.PP
\fIProc\fR must return an integer code that is expected to be one of
\fBTCL_OK\fR, \fBTCL_ERROR\fR, \fBTCL_RETURN\fR, \fBTCL_BREAK\fR, or
\fBTCL_CONTINUE\fR.  See the Tcl overview man page
for details on what these codes mean.  Most normal commands will only
return \fBTCL_OK\fR or \fBTCL_ERROR\fR.  In addition, \fIproc\fR must set
the interpreter result;
in the case of a \fBTCL_OK\fR return code this gives the result
of the command, and in the case of \fBTCL_ERROR\fR it gives an error message.
The \fBTcl_SetResult\fR procedure provides an easy interface for setting
the return value;  for complete details on how the interpreter result
field is managed, see the \fBTcl_Interp\fR man page.
Before invoking a command procedure,
\fBTcl_Eval\fR sets the interpreter result to point to an empty string,
so simple commands can return an empty result by doing nothing at all.
.PP
The contents of the \fIargv\fR array belong to Tcl and are not
guaranteed to persist once \fIproc\fR returns:  \fIproc\fR should
not modify them, nor should it set the interpreter result to point
anywhere within the \fIargv\fR values.
Call \fBTcl_SetResult\fR with status \fBTCL_VOLATILE\fR if you want
to return something from the \fIargv\fR array.
.PP
\fIDeleteProc\fR will be invoked when (if) \fIcmdName\fR is deleted. This can
occur through a call to \fBTcl_DeleteCommand\fR or \fBTcl_DeleteInterp\fR,
or by replacing \fIcmdName\fR in another call to \fBTcl_CreateCommand\fR.
\fIDeleteProc\fR is invoked before the command is deleted, and gives the
application an opportunity to release any structures associated
with the command.  \fIDeleteProc\fR should have arguments and
result that match the type \fBTcl_CmdDeleteProc\fR:
.PP
.CS
typedef void \fBTcl_CmdDeleteProc\fR(
        ClientData \fIclientData\fR);
.CE
.PP
The \fIclientData\fR argument will be the same as the \fIclientData\fR
argument passed to \fBTcl_CreateCommand\fR.
.SH "SEE ALSO"
Tcl_CreateObjCommand, Tcl_DeleteCommand, Tcl_GetCommandInfo,
Tcl_SetCommandInfo, Tcl_GetCommandName, Tcl_SetObjResult
.SH KEYWORDS
bind, command, create, delete, interpreter, namespace