1Tcl_LinkVar(3) Tcl Library Procedures Tcl_LinkVar(3)
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6
8 Tcl_LinkVar, Tcl_UnlinkVar, Tcl_UpdateLinkedVar - link Tcl variable to
9 C variable
10
12 #include <tcl.h>
13 int
15 Tcl_LinkVar(interp, varName, addr, type)
16 Tcl_UnlinkVar(interp, varName)
18 Tcl_UpdateLinkedVar(interp, varName)
20
22 Tcl_Interp *interp (in) Interpreter that contains varName.
23 Also used by Tcl_LinkVar to return
24 error messages.
25 CONST char *varName (in) Name of global variable.
27 char *addr (in) Address of C variable that is to be
29 linked to varName.
30 int type (in) Type of C variable. Must be one of
32 TCL_LINK_INT, TCL_LINK_DOUBLE, │
33 TCL_LINK_WIDE_INT, TCL_LINK_BOOLEAN,
34 or TCL_LINK_STRING, optionally OR'ed
35 with TCL_LINK_READ_ONLY to make Tcl
36 variable read-only.
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38
41 Tcl_LinkVar uses variable traces to keep the Tcl variable named by var‐
42 Name in sync with the C variable at the address given by addr. When‐
43 ever the Tcl variable is read the value of the C variable will be
44 returned, and whenever the Tcl variable is written the C variable will
45 be updated to have the same value. Tcl_LinkVar normally returns
46 TCL_OK; if an error occurs while setting up the link (e.g. because
47 varName is the name of array) then TCL_ERROR is returned and the inter‐
48 preter's result contains an error message.
49 The type argument specifies the type of the C variable, and must have
51 one of the following values, optionally OR'ed with TCL_LINK_READ_ONLY:
52 TCL_LINK_INT
54 The C variable is of type int. Any value written into the Tcl
55 variable must have a proper integer form acceptable to Tcl_Get‐
56 IntFromObj; attempts to write non-integer values into varName
57 will be rejected with Tcl errors.
58 TCL_LINK_DOUBLE
60 The C variable is of type double. Any value written into the
61 Tcl variable must have a proper real form acceptable to Tcl_Get‐
62 DoubleFromObj; attempts to write non-real values into varName
63 will be rejected with Tcl errors.
64 TCL_LINK_WIDE_INT
66 The C variable is of type Tcl_WideInt (which is an integer type │
67 at least 64-bits wide on all platforms that can support it.) │
68 Any value written into the Tcl variable must have a proper inte‐ │
69 ger form acceptable to Tcl_GetWideIntFromObj; attempts to write │
70 non-integer values into varName will be rejected with Tcl │
71 errors.
72 TCL_LINK_BOOLEAN
74 The C variable is of type int. If its value is zero then it
75 will read from Tcl as ``0''; otherwise it will read from Tcl as
76 ``1''. Whenever varName is modified, the C variable will be set
77 to a 0 or 1 value. Any value written into the Tcl variable must
78 have a proper boolean form acceptable to Tcl_GetBooleanFromObj;
79 attempts to write non-boolean values into varName will be
80 rejected with Tcl errors.
81 TCL_LINK_STRING
83 The C variable is of type char *. If its value is not NULL then │
84 it must be a pointer to a string allocated with Tcl_Alloc or │
85 ckalloc. Whenever the Tcl variable is modified the current C
86 string will be freed and new memory will be allocated to hold a
87 copy of the variable's new value. If the C variable contains a
88 NULL pointer then the Tcl variable will read as ``NULL''.
89 If the TCL_LINK_READ_ONLY flag is present in type then the variable
91 will be read-only from Tcl, so that its value can only be changed by
92 modifying the C variable. Attempts to write the variable from Tcl will
93 be rejected with errors.
94 Tcl_UnlinkVar removes the link previously set up for the variable given
96 by varName. If there does not exist a link for varName then the proce‐
97 dure has no effect.
98 Tcl_UpdateLinkedVar may be invoked after the C variable has changed to
100 force the Tcl variable to be updated immediately. In many cases this
101 procedure is not needed, since any attempt to read the Tcl variable
102 will return the latest value of the C variable. However, if a trace
103 has been set on the Tcl variable (such as a Tk widget that wishes to
104 display the value of the variable), the trace will not trigger when the
105 C variable has changed. Tcl_UpdateLinkedVar ensures that any traces on
106 the Tcl variable are invoked.
107
110 boolean, integer, link, read-only, real, string, traces, variable
111Tcl 7.5 Tcl_LinkVar(3)