1Tcl_CreateCommand(3) Tcl Library Procedures Tcl_CreateCommand(3)
2______________________________________________________________________________
6
8 Tcl_CreateCommand - implement new commands in C
9
11 #include <tcl.h>
12 Tcl_Command
14 Tcl_CreateCommand(interp, cmdName, proc, clientData, deleteProc)
15
17 Tcl_Interp *interp (in) Interpreter in which to
18 create new command.
19 const char *cmdName (in) Name of command.
21 Tcl_CmdProc *proc (in) Implementation of new com‐
23 mand: proc will be called
24 whenever cmdName is invoked
25 as a command.
26 ClientData clientData (in) Arbitrary one-word value to
28 pass to proc and
29 deleteProc.
30 Tcl_CmdDeleteProc *deleteProc (in) Procedure to call before
32 cmdName is deleted from the
33 interpreter; allows for
34 command-specific cleanup.
35 If NULL, then no procedure
36 is called before the com‐
37 mand is deleted.
38______________________________________________________________________________
39
41 Tcl_CreateCommand defines a new command in interp and associates it
42 with procedure proc such that whenever cmdName is invoked as a Tcl com‐
43 mand (via a call to Tcl_Eval) the Tcl interpreter will call proc to
44 process the command. It differs from Tcl_CreateObjCommand in that a
45 new string-based command is defined; that is, a command procedure is
46 defined that takes an array of argument strings instead of values. The
47 value-based command procedures registered by Tcl_CreateObjCommand can
48 execute significantly faster than the string-based command procedures
49 defined by Tcl_CreateCommand. This is because they take Tcl values as
50 arguments and those values can retain an internal representation that
51 can be manipulated more efficiently. Also, Tcl's interpreter now uses
52 values internally. In order to invoke a string-based command procedure
53 registered by Tcl_CreateCommand, it must generate and fetch a string
54 representation from each argument value before the call. New commands
55 should be defined using Tcl_CreateObjCommand. We support Tcl_Create‐
56 Command for backwards compatibility.
57 The procedures Tcl_DeleteCommand, Tcl_GetCommandInfo, and Tcl_SetCom‐
59 mandInfo are used in conjunction with Tcl_CreateCommand.
60 Tcl_CreateCommand will delete an existing command cmdName, if one is
62 already associated with the interpreter. It returns a token that may
63 be used to refer to the command in subsequent calls to Tcl_GetCommand‐
64 Name. If cmdName contains any :: namespace qualifiers, then the com‐
65 mand is added to the specified namespace; otherwise the command is
66 added to the global namespace. If Tcl_CreateCommand is called for an
67 interpreter that is in the process of being deleted, then it does not
68 create a new command and it returns NULL. Proc should have arguments
69 and result that match the type Tcl_CmdProc:
70 typedef int Tcl_CmdProc(
72 ClientData clientData,
73 Tcl_Interp *interp,
74 int argc,
75 const char *argv[]);
76 When proc is invoked the clientData and interp parameters will be
78 copies of the clientData and interp arguments given to Tcl_CreateCom‐
79 mand. Typically, clientData points to an application-specific data
80 structure that describes what to do when the command procedure is
81 invoked. Argc and argv describe the arguments to the command, argc
82 giving the number of arguments (including the command name) and argv
83 giving the values of the arguments as strings. The argv array will
84 contain argc+1 values; the first argc values point to the argument
85 strings, and the last value is NULL. Note that the argument strings
86 should not be modified as they may point to constant strings or may be
87 shared with other parts of the interpreter.
88 Note that the argument strings are encoded in normalized UTF-8 since
90 version 8.1 of Tcl.
91 Proc must return an integer code that is expected to be one of TCL_OK,
93 TCL_ERROR, TCL_RETURN, TCL_BREAK, or TCL_CONTINUE. See the Tcl over‐
94 view man page for details on what these codes mean. Most normal com‐
95 mands will only return TCL_OK or TCL_ERROR. In addition, proc must set
96 the interpreter result; in the case of a TCL_OK return code this gives
97 the result of the command, and in the case of TCL_ERROR it gives an
98 error message. The Tcl_SetResult procedure provides an easy interface
99 for setting the return value; for complete details on how the inter‐
100 preter result field is managed, see the Tcl_Interp man page. Before
101 invoking a command procedure, Tcl_Eval sets the interpreter result to
102 point to an empty string, so simple commands can return an empty result
103 by doing nothing at all.
104 The contents of the argv array belong to Tcl and are not guaranteed to
106 persist once proc returns: proc should not modify them, nor should it
107 set the interpreter result to point anywhere within the argv values.
108 Call Tcl_SetResult with status TCL_VOLATILE if you want to return some‐
109 thing from the argv array.
110 DeleteProc will be invoked when (if) cmdName is deleted. This can occur
112 through a call to Tcl_DeleteCommand or Tcl_DeleteInterp, or by replac‐
113 ing cmdName in another call to Tcl_CreateCommand. DeleteProc is
114 invoked before the command is deleted, and gives the application an
115 opportunity to release any structures associated with the command.
116 DeleteProc should have arguments and result that match the type
117 Tcl_CmdDeleteProc:
118 typedef void Tcl_CmdDeleteProc(
120 ClientData clientData);
121 The clientData argument will be the same as the clientData argument
123 passed to Tcl_CreateCommand.
124
126 Tcl_CreateObjCommand, Tcl_DeleteCommand, Tcl_GetCommandInfo, Tcl_Set‐
127 CommandInfo, Tcl_GetCommandName, Tcl_SetObjResult
128
130 bind, command, create, delete, interpreter, namespace
131Tcl Tcl_CreateCommand(3)