1Tcl_Main(3)                 Tcl Library Procedures                 Tcl_Main(3)
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NAME

8       Tcl_Main,  Tcl_SetMainLoop - main program and event loop definition for
9       Tcl-based applications
10

SYNOPSIS

12       #include <tcl.h>
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14       Tcl_Main(argc, argv, appInitProc)
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16       Tcl_SetMainLoop(mainLoopProc)
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ARGUMENTS

19       int argc (in)                                Number  of   elements   in
20                                                    argv.
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22       char *argv[] (in)                            Array  of strings contain‐
23                                                    ing   command-line   argu‐
24                                                    ments.
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26       Tcl_AppInitProc *appInitProc (in)            Address of an application-
27                                                    specific    initialization
28                                                    procedure.   The value for
29                                                    this argument  is  usually
30                                                    Tcl_AppInit.
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32       Tcl_MainLoopProc *mainLoopProc (in)          Address of an application-
33                                                    specific event loop proce‐
34                                                    dure.
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DESCRIPTION

39       Tcl_Main  can  serve  as  the main program for Tcl-based shell applica‐
40       tions.  A “shell application” is a program like tclsh or wish that sup‐
41       ports both interactive interpretation of Tcl and evaluation of a script
42       contained in a file given as a  command  line  argument.   Tcl_Main  is
43       offered  as  a convenience to developers of shell applications, so they
44       do not have to reproduce all of the code for proper  initialization  of
45       the  Tcl  library  and  interactive  shell  operation.  Other styles of
46       embedding Tcl in an application are not supported by  Tcl_Main.   Those
47       must  be  achieved  by calling lower level functions in the Tcl library
48       directly.
49
50       The Tcl_Main function has been offered by the Tcl library since release
51       Tcl  7.4.   In  older releases of Tcl, the Tcl library itself defined a
52       function main, but that lacks flexibility of embedding style and having
53       a  function  main  in  a library (particularly a shared library) causes
54       problems on many systems.  Having main in the Tcl  library  would  also
55       make  it  hard to use Tcl in C++ programs, since C++ programs must have
56       special C++ main functions.
57
58       Normally each shell application contains a  small  main  function  that
59       does  nothing  but invoke Tcl_Main.  Tcl_Main then does all the work of
60       creating and running a tclsh-like application.
61
62       Tcl_Main is not provided by the public interface of Tcl's stub library.
63       Programs  that  call  Tcl_Main  must be linked against the standard Tcl
64       library.  Extensions (stub-enabled or not) are  not  intended  to  call
65       Tcl_Main.
66
67       Tcl_Main is not thread-safe.  It should only be called by a single mas‐
68       ter thread of a multi-threaded application.  This restriction is not  a
69       problem with normal use described above.
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71       Tcl_Main  and therefore all applications based upon it, like tclsh, use
72       Tcl_GetStdChannel to initialize the standard channels to their  default
73       values. See Tcl_StandardChannels for more information.
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75       Tcl_Main  supports  two  modes of operation, depending on the values of
76       argc and argv.  If the first few arguments  in  argv  match  ?-encoding
77       name?  fileName,  where  fileName  does not begin with the character -,
78       then fileName is taken to be the name of a file  containing  a  startup
79       script,  and  name  is taken to be the name of the encoding of the con‐
80       tents of that file, which Tcl_Main will attempt  to  evaluate.   Other‐
81       wise, Tcl_Main will enter an interactive mode.
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83       In  either mode, Tcl_Main will define in its master interpreter the Tcl
84       variables argc, argv, argv0, and tcl_interactive, as described  in  the
85       documentation for tclsh.
86
87       When  it  has  finished its own initialization, but before it processes
88       commands, Tcl_Main calls the procedure given by the  appInitProc  argu‐
89       ment.   This procedure provides a “hook” for the application to perform
90       its own initialization of the interpreter created by Tcl_Main, such  as
91       defining  application-specific  commands.   The  procedure must have an
92       interface that matches the type Tcl_AppInitProc:
93              typedef int Tcl_AppInitProc(Tcl_Interp *interp);
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95       AppInitProc is almost always a pointer to Tcl_AppInit; for more details
96       on this procedure, see the documentation for Tcl_AppInit.
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98       When the appInitProc is finished, Tcl_Main enters one of its two modes.
99       If a startup script has been provided, Tcl_Main  attempts  to  evaluate
100       it.   Otherwise,  interactive mode begins with examination of the vari‐
101       able tcl_rcFileName in the master interpreter.  If that variable exists
102       and  holds  the  name of a readable file, the contents of that file are
103       evaluated in  the  master  interpreter.   Then  interactive  operations
104       begin, with prompts and command evaluation results written to the stan‐
105       dard output channel, and commands read from the standard input  channel
106       and then evaluated.  The prompts written to the standard output channel
107       may be  customized  by  defining  the  Tcl  variables  tcl_prompt1  and
108       tcl_prompt2  as  described in the documentation for tclsh.  The prompts
109       and command evaluation results are written to the standard output chan‐
110       nel  only if the Tcl variable tcl_interactive in the master interpreter
111       holds a non-zero integer value.
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113       Tcl_SetMainLoop allows setting an event loop procedure to be run.  This
114       allows,  for  example,  Tk  to  be dynamically loaded and set its event
115       loop.  The event loop will run following the startup  script.   If  you
116       are in interactive mode, setting the main loop procedure will cause the
117       prompt to become fileevent based and then the loop procedure is called.
118       When the loop procedure returns in interactive mode, interactive opera‐
119       tion will continue.  The main loop procedure  must  have  an  interface
120       that matches the type Tcl_MainLoopProc:
121              typedef void Tcl_MainLoopProc(void);
122
123       Tcl_Main  does  not  return.  Normally a program based on Tcl_Main will
124       terminate when the exit command is evaluated.  In interactive mode,  if
125       an  EOF  or channel error is encountered on the standard input channel,
126       then Tcl_Main itself will evaluate the exit command after the main loop
127       procedure  (if  any)  returns.  In non-interactive mode, after Tcl_Main
128       evaluates the startup script, and the  main  loop  procedure  (if  any)
129       returns, Tcl_Main will also evaluate the exit command.
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SEE ALSO

133       tclsh(1),         Tcl_GetStdChannel(3),        Tcl_StandardChannels(3),
134       Tcl_AppInit(3), exit(n)
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KEYWORDS

138       application-specific initialization, command-line arguments, main  pro‐
139       gram
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143Tcl                                   8.4                          Tcl_Main(3)
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