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Tcl_LinkVar(3) Tcl Library Procedures Tcl_LinkVar(3) ________________________________________________________________________________ NAME Tcl_LinkVar, Tcl_UnlinkVar, Tcl_UpdateLinkedVar - link Tcl variable to C variable SYNOPSIS #include <tcl.h> int Tcl_LinkVar(interp, varName, addr, type) Tcl_UnlinkVar(interp, varName) Tcl_UpdateLinkedVar(interp, varName) ARGUMENTS Tcl_Interp *interp (in) Interpreter that contains varName. Also used by Tcl_LinkVar to return error mes- sages. const char *varName (in) Name of global variable. char *addr (in) Address of C variable that is to be linked to varName. int type (in) Type of C variable. Must be one of TCL_LINK_INT, TCL_LINK_UINT, TCL_LINK_CHAR, TCL_LINK_UCHAR, TCL_LINK_SHORT, TCL_LINK_USHORT, TCL_LINK_LONG, TCL_LINK_ULONG, TCL_LINK_WIDE_INT, TCL_LINK_WIDE_UINT, TCL_LINK_FLOAT, TCL_LINK_DOUBLE, TCL_LINK_BOOLEAN, or TCL_LINK_STRING, op- tionally OR'ed with TCL_LINK_READ_ONLY to make Tcl variable read-only. ________________________________________________________________________________ DESCRIPTION Tcl_LinkVar uses variable traces to keep the Tcl variable named by varName in sync with the C variable at the address given by addr. Whenever the Tcl variable is read the value of the C variable will be returned, and whenever the Tcl variable is written the C variable will be updated to have the same value. Tcl_LinkVar normally returns TCL_OK; if an error occurs while set- ting up the link (e.g. because varName is the name of array) then TCL_ERROR is returned and the interpreter's result contains an error message. The type argument specifies the type of the C variable, and must have one of the following values, optionally OR'ed with TCL_LINK_READ_ONLY: TCL_LINK_INT The C variable is of type int. Any value written into the Tcl vari- able must have a proper integer form acceptable to Tcl_GetIntFro- mObj; attempts to write non-integer values into varName will be re- jected with Tcl errors. Incomplete integer representations (like the empty string, '+', '-' or the hex/octal/binary prefix) are accepted as if they are valid too. TCL_LINK_UINT The C variable is of type unsigned int. Any value written into the Tcl variable must have a proper unsigned integer form acceptable to Tcl_GetWideIntFromObj and in the platform's defined range for the unsigned int type; attempts to write non-integer values (or values outside the range) into varName will be rejected with Tcl errors. Incomplete integer representations (like the empty string, '+', '-' or the hex/octal/binary prefix) are accepted as if they are valid too. TCL_LINK_CHAR The C variable is of type char. Any value written into the Tcl variable must have a proper integer form acceptable to Tcl_GetInt- FromObj and be in the range of the char datatype; attempts to write non-integer or out-of-range values into varName will be rejected with Tcl errors. Incomplete integer representations (like the empty string, '+', '-' or the hex/octal/binary prefix) are accepted as if they are valid too. TCL_LINK_UCHAR The C variable is of type unsigned char. Any value written into the Tcl variable must have a proper unsigned integer form acceptable to Tcl_GetIntFromObj and in the platform's defined range for the un- signed char type; attempts to write non-integer values (or values outside the range) into varName will be rejected with Tcl errors. Incomplete integer representations (like the empty string, '+', '-' or the hex/octal/binary prefix) are accepted as if they are valid too. TCL_LINK_SHORT The C variable is of type short. Any value written into the Tcl variable must have a proper integer form acceptable to Tcl_GetInt- FromObj and be in the range of the short datatype; attempts to write non-integer or out-of-range values into varName will be rejected with Tcl errors. Incomplete integer representations (like the empty string, '+', '-' or the hex/octal/binary prefix) are accepted as if they are valid too. TCL_LINK_USHORT The C variable is of type unsigned short. Any value written into the Tcl variable must have a proper unsigned integer form acceptable to Tcl_GetIntFromObj and in the platform's defined range for the un- signed short type; attempts to write non-integer values (or values outside the range) into varName will be rejected with Tcl errors. Incomplete integer representations (like the empty string, '+', '-' or the hex/octal/binary prefix) are accepted as if they are valid too. TCL_LINK_LONG The C variable is of type long. Any value written into the Tcl variable must have a proper integer form acceptable to Tcl_Get- LongFromObj; attempts to write non-integer or out-of-range values into varName will be rejected with Tcl errors. Incomplete integer representations (like the empty string, '+', '-' or the hex/oc- tal/binary prefix) are accepted as if they are valid too. TCL_LINK_ULONG The C variable is of type unsigned long. Any value written into the Tcl variable must have a proper unsigned integer form acceptable to Tcl_GetWideIntFromObj and in the platform's defined range for the unsigned long type; attempts to write non-integer values (or values outside the range) into varName will be rejected with Tcl errors. Incomplete integer representations (like the empty string, '+', '-' or the hex/octal/binary prefix) are accepted as if they are valid too. TCL_LINK_DOUBLE The C variable is of type double. Any value written into the Tcl variable must have a proper real form acceptable to Tcl_GetDouble- FromObj; attempts to write non-real values into varName will be re- jected with Tcl errors. Incomplete integer or real representations (like the empty string, '.', '+', '-' or the hex/octal/binary pre- fix) are accepted as if they are valid too. TCL_LINK_FLOAT The C variable is of type float. Any value written into the Tcl variable must have a proper real form acceptable to Tcl_GetDouble- FromObj and must be within the range acceptable for a float; at- tempts to write non-real values (or values outside the range) into varName will be rejected with Tcl errors. Incomplete integer or real representations (like the empty string, '.', '+', '-' or the hex/oc- tal/binary prefix) are accepted as if they are valid too. TCL_LINK_WIDE_INT The C variable is of type Tcl_WideInt (which is an integer type at least 64-bits wide on all platforms that can support it.) Any value written into the Tcl variable must have a proper integer form ac- ceptable to Tcl_GetWideIntFromObj; attempts to write non-integer values into varName will be rejected with Tcl errors. Incomplete in- teger representations (like the empty string, '+', '-' or the hex/octal/binary prefix) are accepted as if they are valid too. TCL_LINK_WIDE_UINT The C variable is of type Tcl_WideUInt (which is an unsigned integer type at least 64-bits wide on all platforms that can support it.) Any value written into the Tcl variable must have a proper unsigned integer form acceptable to Tcl_GetWideIntFromObj (it will be cast to unsigned); attempts to write non-integer values into varName will be rejected with Tcl errors. Incomplete integer representations (like the empty string, '+', '-' or the hex/octal/binary prefix) are ac- cepted as if they are valid too. TCL_LINK_BOOLEAN The C variable is of type int. If its value is zero then it will read from Tcl as "0"; otherwise it will read from Tcl as "1". When- ever varName is modified, the C variable will be set to a 0 or 1 value. Any value written into the Tcl variable must have a proper boolean form acceptable to Tcl_GetBooleanFromObj; attempts to write non-boolean values into varName will be rejected with Tcl errors. TCL_LINK_STRING The C variable is of type char *. If its value is not NULL then it must be a pointer to a string allocated with Tcl_Alloc or ckalloc. Whenever the Tcl variable is modified the current C string will be freed and new memory will be allocated to hold a copy of the vari- able's new value. If the C variable contains a NULL pointer then the Tcl variable will read as "NULL". If the TCL_LINK_READ_ONLY flag is present in type then the variable will be read-only from Tcl, so that its value can only be changed by modifying the C variable. Attempts to write the variable from Tcl will be rejected with errors. Tcl_UnlinkVar removes the link previously set up for the variable given by varName. If there does not exist a link for varName then the procedure has no effect. Tcl_UpdateLinkedVar may be invoked after the C variable has changed to force the Tcl variable to be updated immediately. In many cases this pro- cedure is not needed, since any attempt to read the Tcl variable will re- turn the latest value of the C variable. However, if a trace has been set on the Tcl variable (such as a Tk widget that wishes to display the value of the variable), the trace will not trigger when the C variable has changed. Tcl_UpdateLinkedVar ensures that any traces on the Tcl variable are invoked. Note that, as with any call to a Tcl interpreter, Tcl_UpdateLinkedVar must be called from the same thread that created the interpreter. The safest mechanism is to ensure that the C variable is only ever updated from the same thread that created the interpreter (possibly in response to an event posted with Tcl_ThreadQueueEvent), but when it is necessary to update the variable in a separate thread, it is advised that Tcl_AsyncMark be used to indicate to the thread hosting the interpreter that it is ready to run Tcl_UpdateLinkedVar. SEE ALSO Tcl_TraceVar(3) KEYWORDS boolean, integer, link, read-only, real, string, trace, variable Tcl 7.5 Tcl_LinkVar(3)
NAME | SYNOPSIS | ARGUMENTS | DESCRIPTION | SEE ALSO | KEYWORDS
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