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+'\"
+'\" Copyright (c) 2003 Donal K. Fellows
+'\"
+'\" See the file "license.terms" for information on usage and redistribution
+'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
+'\" 
+'\" RCS: @(#) $Id: DictObj.3,v 1.11.2.2 2009/11/27 14:53:54 dkf Exp $
+'\" 
+.so man.macros
+.TH Tcl_DictObj 3 8.5 Tcl "Tcl Library Procedures"
+.BS
+'\" Note:  do not modify the .SH NAME line immediately below!
+.SH NAME
+Tcl_NewDictObj, Tcl_DictObjPut, Tcl_DictObjGet, Tcl_DictObjRemove, Tcl_DictObjSize, Tcl_DictObjFirst, Tcl_DictObjNext, Tcl_DictObjDone, Tcl_DictObjPutKeyList, Tcl_DictObjRemoveKeyList \- manipulate Tcl objects as dictionaries
+.SH SYNOPSIS
+.nf
+\fB#include <tcl.h>\fR
+.sp
+Tcl_Obj *
+\fBTcl_NewDictObj\fR()
+.sp
+int
+\fBTcl_DictObjGet\fR(\fIinterp, dictPtr, keyPtr, valuePtrPtr\fR)
+.sp
+int
+\fBTcl_DictObjPut\fR(\fIinterp, dictPtr, keyPtr, valuePtr\fR)
+.sp
+int
+\fBTcl_DictObjRemove\fR(\fIinterp, dictPtr, keyPtr\fR)
+.sp
+int
+\fBTcl_DictObjSize\fR(\fIinterp, dictPtr, sizePtr\fR)
+.sp
+int
+\fBTcl_DictObjFirst\fR(\fIinterp, dictPtr, searchPtr,
+                 keyPtrPtr, valuePtrPtr, donePtr\fR)
+.sp
+void
+\fBTcl_DictObjNext\fR(\fIsearchPtr, keyPtrPtr, valuePtrPtr, donePtr\fR)
+.sp
+void
+\fBTcl_DictObjDone\fR(\fIsearchPtr\fR)
+.sp
+int
+\fBTcl_DictObjPutKeyList\fR(\fIinterp, dictPtr, keyc, keyv, valuePtr\fR)
+.sp
+int
+\fBTcl_DictObjRemoveKeyList\fR(\fIinterp, dictPtr, keyc, keyv\fR)
+.SH ARGUMENTS
+.AS Tcl_DictSearch "**valuePtrPtr" in/out
+.AP Tcl_Interp *interp in
+If an error occurs while converting an object to be a dictionary object,
+an error message is left in the interpreter's result object
+unless \fIinterp\fR is NULL.
+.AP Tcl_Obj *dictPtr in/out
+Points to the dictionary object to be manipulated.
+If \fIdictPtr\fR does not already point to a dictionary object,
+an attempt will be made to convert it to one.
+.AP Tcl_Obj *keyPtr in
+Points to the key for the key/value pair being manipulated within the
+dictionary object.
+.AP Tcl_Obj **keyPtrPtr out
+Points to a variable that will have the key from a key/value pair
+placed within it.  May be NULL to indicate that the caller is not
+interested in the key.
+.AP Tcl_Obj *valuePtr in
+Points to the value for the key/value pair being manipulate within the
+dictionary object (or sub-object, in the case of
+\fBTcl_DictObjPutKeyList\fR.)
+.AP Tcl_Obj **valuePtrPtr out
+Points to a variable that will have the value from a key/value pair
+placed within it.  For \fBTcl_DictObjFirst\fR and
+\fBTcl_DictObjNext\fR, this may be NULL to indicate that the caller is
+not interested in the value.
+.AP int *sizePtr out
+Points to a variable that will have the number of key/value pairs
+contained within the dictionary placed within it.
+.AP Tcl_DictSearch *searchPtr in/out
+Pointer to record to use to keep track of progress in enumerating all
+key/value pairs in a dictionary.  The contents of the record will be
+initialized by the call to \fBTcl_DictObjFirst\fR.  If the enumerating
+is to be terminated before all values in the dictionary have been
+returned, the search record \fImust\fR be passed to
+\fBTcl_DictObjDone\fR to enable the internal locks to be released.
+.AP int *donePtr out
+Points to a variable that will have a non-zero value written into it
+when the enumeration of the key/value pairs in a dictionary has
+completed, and a zero otherwise.
+.AP int keyc in
+Indicates the number of keys that will be supplied in the \fIkeyv\fR
+array.
+.AP "Tcl_Obj *const" *keyv in
+Array of \fIkeyc\fR pointers to objects that
+\fBTcl_DictObjPutKeyList\fR and \fBTcl_DictObjRemoveKeyList\fR will
+use to locate the key/value pair to manipulate within the
+sub-dictionaries of the main dictionary object passed to them.
+.BE
+
+.SH DESCRIPTION
+.PP
+Tcl dictionary objects have an internal representation that supports
+efficient mapping from keys to values and which guarantees that the
+particular ordering of keys within the dictionary remains the same
+modulo any keys being deleted (which removes them from the order) or
+added (which adds them to the end of the order). If reinterpreted as a
+list, the values at the even-valued indices in the list will be the
+keys of the dictionary, and each will be followed (in the odd-valued
+index) by the value associated with that key.
+.PP
+The procedures described in this man page are used to
+create, modify, index, and iterate over dictionary objects from C code.
+.PP
+\fBTcl_NewDictObj\fR creates a new, empty dictionary object.  The
+string representation of the object will be invalid, and the reference
+count of the object will be zero.
+.PP
+\fBTcl_DictObjGet\fR looks up the given key within the given
+dictionary and writes a pointer to the value associated with that key
+into the variable pointed to by \fIvaluePtrPtr\fR, or a NULL if the
+key has no mapping within the dictionary.  The result of this
+procedure is \fBTCL_OK\fR, or \fBTCL_ERROR\fR if the \fIdictPtr\fR cannot be
+converted to a dictionary.
+.PP
+\fBTcl_DictObjPut\fR updates the given dictionary so that the given
+key maps to the given value; any key may exist at most once in any
+particular dictionary.  The dictionary must not be shared, but the key
+and value may be.  This procedure may increase the reference count of
+both key and value if it proves necessary to store them.  Neither key
+nor value should be NULL.  The result of this procedure is \fBTCL_OK\fR, or
+\fBTCL_ERROR\fR if the \fIdictPtr\fR cannot be converted to a dictionary.
+.PP
+\fBTcl_DictObjRemove\fR updates the given dictionary so that the given
+key has no mapping to any value.  The dictionary must not be shared,
+but the key may be.  The key actually stored in the dictionary will
+have its reference count decremented if it was present.  It is not an
+error if the key did not previously exist.  The result of this
+procedure is \fBTCL_OK\fR, or \fBTCL_ERROR\fR if the \fIdictPtr\fR cannot be
+converted to a dictionary.
+.PP
+\fBTcl_DictObjSize\fR updates the given variable with the number of
+key/value pairs currently in the given dictionary. The result of this
+procedure is \fBTCL_OK\fR, or \fBTCL_ERROR\fR if the \fIdictPtr\fR cannot be
+converted to a dictionary.
+.PP
+\fBTcl_DictObjFirst\fR commences an iteration across all the key/value
+pairs in the given dictionary, placing the key and value in the
+variables pointed to by the \fIkeyPtrPtr\fR and \fIvaluePtrPtr\fR
+arguments (which may be NULL to indicate that the caller is
+uninterested in they key or variable respectively.)  The next
+key/value pair in the dictionary may be retrieved with
+\fBTcl_DictObjNext\fR.  Concurrent updates of the dictionary's
+internal representation will not modify the iteration processing
+unless the dictionary is unshared, when this will trigger premature
+termination of the iteration instead (which Tcl scripts cannot trigger
+via the \fBdict\fR command.)  The \fIsearchPtr\fR argument points to a
+piece of context that is used to identify which particular iteration
+is being performed, and is initialized by the call to
+\fBTcl_DictObjFirst\fR.  The \fIdonePtr\fR argument points to a
+variable that is updated to be zero of there are further key/value
+pairs to be iterated over, or non-zero if the iteration is complete.
+The order of iteration is implementation-defined.  If the
+\fIdictPtr\fR argument cannot be converted to a dictionary,
+\fBTcl_DictObjFirst\fR returns \fBTCL_ERROR\fR and the iteration is not
+commenced, and otherwise it returns \fBTCL_OK\fR.
+.PP
+When \fBTcl_DictObjFirst\fR is called upon a dictionary, a lock is placed on
+the dictionary to enable that dictionary to be iterated over safely without
+regard for whether the dictionary is modified during the iteration. Because of
+this, once the iteration over a dictionary's keys has finished (whether
+because all values have been iterated over as indicated by the variable
+indicated by the \fIdonePtr\fR argument being set to one, or because no
+further values are required) the \fBTcl_DictObjDone\fR function must be called
+with the same \fIsearchPtr\fR as was passed to \fBTcl_DictObjFirst\fR so that
+the internal locks can be released. Once a particular \fIsearchPtr\fR is
+passed to \fBTcl_DictObjDone\fR, passing it to \fBTcl_DictObjNext\fR (without
+first initializing it with \fBTcl_DictObjFirst\fR) will result in no values
+being produced and the variable pointed to by \fIdonePtr\fR being set to one.
+It is safe to call \fBTcl_DictObjDone\fR multiple times on the same
+\fIsearchPtr\fR for each call to \fBTcl_DictObjFirst\fR.
+.PP
+The procedures \fBTcl_DictObjPutKeyList\fR and
+\fBTcl_DictObjRemoveKeyList\fR are the close analogues of
+\fBTcl_DictObjPut\fR and \fBTcl_DictObjRemove\fR respectively, except
+that instead of working with a single dictionary, they are designed to
+operate on a nested tree of dictionaries, with inner dictionaries
+stored as values inside outer dictionaries.  The \fIkeyc\fR and
+\fIkeyv\fR arguments specify a list of keys (with outermost keys
+first) that acts as a path to the key/value pair to be affected.  Note
+that there is no corresponding operation for reading a value for a
+path as this is easy to construct from repeated use of
+\fBTcl_DictObjGet\fR. With \fBTcl_DictObjPutKeyList\fR, nested
+dictionaries are created for non-terminal keys where they do not
+already exist. With \fBTcl_DictObjRemoveKeyList\fR, all non-terminal
+keys must exist and have dictionaries as their values.
+.SH EXAMPLE
+Using the dictionary iteration interface to search determine if there
+is a key that maps to itself:
+.PP
+.CS
+Tcl_DictSearch search;
+Tcl_Obj *key, *value;
+int done;
+
+/*
+ * Assume interp and objPtr are parameters.  This is the
+ * idiomatic way to start an iteration over the dictionary; it
+ * sets a lock on the internal representation that ensures that
+ * there are no concurrent modification issues when normal
+ * reference count management is also used.  The lock is
+ * released automatically when the loop is finished, but must
+ * be released manually when an exceptional exit from the loop
+ * is performed. However it is safe to try to release the lock
+ * even if we've finished iterating over the loop.
+ */
+if (\fBTcl_DictObjFirst\fR(interp, objPtr, &search,
+        &key, &value, &done) != TCL_OK) {
+    return TCL_ERROR;
+}
+for (; !done ; \fBTcl_DictObjNext\fR(&search, &key, &value, &done)) {
+    /*
+     * Note that strcmp() is not a good way of comparing
+     * objects and is just used here for demonstration
+     * purposes.
+     */
+    if (!strcmp(Tcl_GetString(key), Tcl_GetString(value))) {
+        break;
+    }
+}
+\fBTcl_DictObjDone\fR(&search);
+Tcl_SetObjResult(interp, Tcl_NewBooleanObj(!done));
+return TCL_OK;
+.CE
+.SH "SEE ALSO"
+Tcl_NewObj, Tcl_DecrRefCount, Tcl_IncrRefCount, Tcl_InitObjHashTable
+.SH KEYWORDS
+dict, dict object, dictionary, dictionary object, hash table, iteration, object