DOKK / manpages / debian 13 / tcl9.0-doc / Tcl_UpdateLinkedVar.3tcl.en
Tcl_LinkVar(3tcl) Tcl Library Procedures Tcl_LinkVar(3tcl) 







Tcl_LinkArray, Tcl_LinkVar, Tcl_UnlinkVar, Tcl_UpdateLinkedVar -
    link Tcl variable to C variable








#include <tcl.h>

int
Tcl_LinkVar(interp, varName, addr, type)

int
Tcl_LinkArray(interp, varName, addr, type, size)

Tcl_UnlinkVar(interp, varName)

Tcl_UpdateLinkedVar(interp, varName)









  
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.

  
void *addr (in)

  
Address of C variable that is to be linked to varName.
    
In Tcl_LinkArray, may be NULL to tell Tcl to create the
        storage for the array in the variable.

  

  
int type (in)

  
Type of C variable for Tcl_LinkVar or type of array element for
      Tcl_LinkArray. 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 one of the extra ones listed below.
    
In Tcl_LinkVar, the additional linked type
        TCL_LINK_STRING may be used.

    
In Tcl_LinkArray, the additional linked types
        TCL_LINK_CHARS and TCL_LINK_BINARY may be used.

    
All the above for both functions may be optionally OR'ed with
        TCL_LINK_READ_ONLY to make the Tcl variable read-only.

  

  
Tcl_Size size (in)

  
The number of elements in the C array. Must be greater than zero.
    
    

    

  










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 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.


Tcl_LinkArray is similar, but for arrays of fixed size
    (given by the size argument). When asked to allocate the backing C
    array storage (via the addr argument being NULL), it writes the
    address that it allocated to the Tcl interpreter result.


The type argument specifies the type of the C variable, or
    the type of the elements of the C array, and must have one of the following
    values, optionally OR'ed with TCL_LINK_READ_ONLY:



  
  
The C variable, or each element of the C array, 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. Incomplete
      integer representations (like the empty string, '+', '-' or the
      hex/octal/decimal/binary prefix) are accepted as if they are valid
    too.

  
  
The C variable, or each element of the C array, 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/decimal/binary prefix) are
      accepted as if they are valid too.

  
  
The C variable, or each element of the C array, 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. Incomplete integer
      representations (like the empty string, '+', '-' or the
      hex/octal/decimal/binary prefix) are accepted as if they are valid
    too.






If using an array of these, consider using TCL_LINK_CHARS
    instead.





  
  
The C array is of type char * and is mapped into Tcl as a string.
      Any value written into the Tcl variable must have the same length as the
      underlying storage. Only supported with Tcl_LinkArray.

  
  
The C variable, or each element of the C array, 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. Incomplete integer representations (like
      the empty string, '+', '-' or the hex/octal/decimal/binary prefix) are
      accepted as if they are valid too.






If using an array of these, consider using TCL_LINK_BINARY
    instead.





  
  
The C array is of type unsigned char * and is mapped into Tcl as a
      bytearray. Any value written into the Tcl variable must have the same
      length as the underlying storage. Only supported with
      Tcl_LinkArray.

  
  
The C variable, or each element of the C array, 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. Incomplete
      integer representations (like the empty string, '+', '-' or the
      hex/octal/decimal/binary prefix) are accepted as if they are valid
    too.

  
  
The C variable, or each element of the C array, 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. Incomplete integer representations (like
      the empty string, '+', '-' or the hex/octal/decimal/binary prefix) are
      accepted as if they are valid too.

  
  
The C variable, or each element of the C array, 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-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/decimal/binary prefix) are accepted as if they are valid
    too.

  
  
The C variable, or each element of the C array, 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/decimal/binary prefix) are accepted as if they are valid
    too.

  
  
The C variable, or each element of the C array, 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. Incomplete
      integer or real representations (like the empty string, '.', '+', '-' or
      the hex/octal/decimal/binary prefix) are accepted as if they are valid
      too.

  
  
The C variable, or each element of the C array, 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. Incomplete integer or real representations (like the empty string,
      '.', '+', '-' or the hex/octal/decimal/binary prefix) are accepted as if
      they are valid too.

  
  
The C variable, or each element of the C array, 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 acceptable to
      Tcl_GetWideIntFromObj; 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/decimal/binary prefix) are accepted as if they are valid
    too.

  
  
The C variable, or each element of the C array, 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 wideinteger form acceptable to
      Tcl_GetWideUIntFromObj; 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/decimal/binary prefix) are accepted as if they are valid
    too.

  
  
The C variable, or each element of the C array, 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.

  
  
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. 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”. This is only supported by Tcl_LinkVar.




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 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.


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.








Tcl_TraceVar(3tcl)








boolean, integer, link, read-only, real, string, trace,
  variable







  

    7.5
    Tcl