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 messages. 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, optionally 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 vari- able will be updated to have the same value. Tcl_LinkVar normally returns TCL_OK; if an error occurs while setting 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 variable must have a proper integer form acceptable to Tcl_GetIntFromObj; attempts to write non-integer values into varName will be rejected with Tcl errors. | 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-inte- | ger values (or values outside the range) into varName will be rejected with Tcl | errors. | 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_GetIntFromObj 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. | 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 unsigned char type; attempts to write non-integer | values (or values outside the range) into varName will be rejected with Tcl errors. | 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_GetIntFromObj 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. | 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 unsigned short type; attempts to write non-integer | values (or values outside the range) into varName will be rejected with Tcl errors. | 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_GetLongFromObj; attempts to write non-inte- | ger or out-of-range values into varName will be rejected with Tcl errors. | 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. 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_GetDoubleFromObj; attempts to write non- real values into varName will be rejected with Tcl errors. | 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_GetDoubleFromObj and must be within the range | acceptable for a float; attempts to write non-real values (or values outside the | range) into varName will be rejected with Tcl errors. 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 vari- able must have a proper integer form acceptable to Tcl_GetWideIntFromObj; attempts to write non-integer values into varName will be rejected with Tcl errors. | 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_GetWideIntFro- | mObj (it will be cast to unsigned); attempts to write non-integer values into var- | Name will be rejected with Tcl errors. 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". Whenever 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 variable'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 vari- able to be updated immediately. In many cases this procedure is not needed, since any attempt to read the Tcl variable will return 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. KEYWORDS boolean, integer, link, read-only, real, string, traces, variable Tcl 7.5 Tcl_LinkVar(3)