shared_source/c_tcl_base_7_5_w_mods/tcllink.c

/* $Header$ */
/* 
 * tclLink.c --
 *
 *      This file implements linked variables (a C variable that is
 *      tied to a Tcl variable).  The idea of linked variables was
 *      first suggested by Andreas Stolcke and this implementation is
 *      based heavily on a prototype implementation provided by
 *      him.
 *
 * Copyright (c) 1993 The Regents of the University of California.
 * Copyright (c) 1994-1997 Sun Microsystems, Inc.
 *
 * See the file "license.terms" for information on usage and redistribution
 * of this file, and for a DISCLAIMER OF ALL WARRANTIES.
 *
 * RCS: @(#) $Id: tcllink.c,v 1.1.1.1 2001/06/13 04:42:27 dtashley Exp $
 */

#include "tclInt.h"

/*
 * For each linked variable there is a data structure of the following
 * type, which describes the link and is the clientData for the trace
 * set on the Tcl variable.
 */

typedef struct Link {
    Tcl_Interp *interp;         /* Interpreter containing Tcl variable. */
    char *varName;              /* Name of variable (must be global).  This
                                 * is needed during trace callbacks, since
                                 * the actual variable may be aliased at
                                 * that time via upvar. */
    char *addr;                 /* Location of C variable. */
    int type;                   /* Type of link (TCL_LINK_INT, etc.). */
    union {
        int i;
        double d;
    } lastValue;                /* Last known value of C variable;  used to
                                 * avoid string conversions. */
    int flags;                  /* Miscellaneous one-bit values;  see below
                                 * for definitions. */
} Link;

/*
 * Definitions for flag bits:
 * LINK_READ_ONLY -             1 means errors should be generated if Tcl
 *                              script attempts to write variable.
 * LINK_BEING_UPDATED -         1 means that a call to Tcl_UpdateLinkedVar
 *                              is in progress for this variable, so
 *                              trace callbacks on the variable should
 *                              be ignored.
 */

#define LINK_READ_ONLY          1
#define LINK_BEING_UPDATED      2

/*
 * Forward references to procedures defined later in this file:
 */

static char *           LinkTraceProc _ANSI_ARGS_((ClientData clientData,
                            Tcl_Interp *interp, char *name1, char *name2,
                            int flags));
static char *           StringValue _ANSI_ARGS_((Link *linkPtr,
                            char *buffer));

/*
 *----------------------------------------------------------------------
 *
 * Tcl_LinkVar --
 *
 *      Link a C variable to a Tcl variable so that changes to either
 *      one causes the other to change.
 *
 * Results:
 *      The return value is TCL_OK if everything went well or TCL_ERROR
 *      if an error occurred (the interp's result is also set after
 *      errors).
 *
 * Side effects:
 *      The value at *addr is linked to the Tcl variable "varName",
 *      using "type" to convert between string values for Tcl and
 *      binary values for *addr.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_LinkVar(interp, varName, addr, type)
    Tcl_Interp *interp;         /* Interpreter in which varName exists. */
    char *varName;              /* Name of a global variable in interp. */
    char *addr;                 /* Address of a C variable to be linked
                                 * to varName. */
    int type;                   /* Type of C variable: TCL_LINK_INT, etc. 
                                 * Also may have TCL_LINK_READ_ONLY
                                 * OR'ed in. */
{
    Link *linkPtr;
    char buffer[TCL_DOUBLE_SPACE];
    int code;

    linkPtr = (Link *) ckalloc(sizeof(Link));
    linkPtr->interp = interp;
    linkPtr->varName = (char *) ckalloc((unsigned) (strlen(varName) + 1));
    strcpy(linkPtr->varName, varName);
    linkPtr->addr = addr;
    linkPtr->type = type & ~TCL_LINK_READ_ONLY;
    if (type & TCL_LINK_READ_ONLY) {
        linkPtr->flags = LINK_READ_ONLY;
    } else {
        linkPtr->flags = 0;
    }
    if (Tcl_SetVar(interp, varName, StringValue(linkPtr, buffer),
            TCL_GLOBAL_ONLY|TCL_LEAVE_ERR_MSG) == NULL) {
        ckfree(linkPtr->varName);
        ckfree((char *) linkPtr);
        return TCL_ERROR;
    }
    code = Tcl_TraceVar(interp, varName, TCL_GLOBAL_ONLY|TCL_TRACE_READS
            |TCL_TRACE_WRITES|TCL_TRACE_UNSETS, LinkTraceProc,
            (ClientData) linkPtr);
    if (code != TCL_OK) {
        ckfree(linkPtr->varName);
        ckfree((char *) linkPtr);
    }
    return code;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_UnlinkVar --
 *
 *      Destroy the link between a Tcl variable and a C variable.
 *
 * Results:
 *      None.
 *
 * Side effects:
 *      If "varName" was previously linked to a C variable, the link
 *      is broken to make the variable independent.  If there was no
 *      previous link for "varName" then nothing happens.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_UnlinkVar(interp, varName)
    Tcl_Interp *interp;         /* Interpreter containing variable to unlink. */
    char *varName;              /* Global variable in interp to unlink. */
{
    Link *linkPtr;

    linkPtr = (Link *) Tcl_VarTraceInfo(interp, varName, TCL_GLOBAL_ONLY,
            LinkTraceProc, (ClientData) NULL);
    if (linkPtr == NULL) {
        return;
    }
    Tcl_UntraceVar(interp, varName,
            TCL_GLOBAL_ONLY|TCL_TRACE_READS|TCL_TRACE_WRITES|TCL_TRACE_UNSETS,
            LinkTraceProc, (ClientData) linkPtr);
    ckfree(linkPtr->varName);
    ckfree((char *) linkPtr);
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_UpdateLinkedVar --
 *
 *      This procedure is invoked after a linked variable has been
 *      changed by C code.  It updates the Tcl variable so that
 *      traces on the variable will trigger.
 *
 * Results:
 *      None.
 *
 * Side effects:
 *      The Tcl variable "varName" is updated from its C value,
 *      causing traces on the variable to trigger.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_UpdateLinkedVar(interp, varName)
    Tcl_Interp *interp;         /* Interpreter containing variable. */
    char *varName;              /* Name of global variable that is linked. */
{
    Link *linkPtr;
    char buffer[TCL_DOUBLE_SPACE];
    int savedFlag;

    linkPtr = (Link *) Tcl_VarTraceInfo(interp, varName, TCL_GLOBAL_ONLY,
            LinkTraceProc, (ClientData) NULL);
    if (linkPtr == NULL) {
        return;
    }
    savedFlag = linkPtr->flags & LINK_BEING_UPDATED;
    linkPtr->flags |= LINK_BEING_UPDATED;
    Tcl_SetVar(interp, linkPtr->varName, StringValue(linkPtr, buffer),
            TCL_GLOBAL_ONLY);
    linkPtr->flags = (linkPtr->flags & ~LINK_BEING_UPDATED) | savedFlag;
}

/*
 *----------------------------------------------------------------------
 *
 * LinkTraceProc --
 *
 *      This procedure is invoked when a linked Tcl variable is read,
 *      written, or unset from Tcl.  It's responsible for keeping the
 *      C variable in sync with the Tcl variable.
 *
 * Results:
 *      If all goes well, NULL is returned; otherwise an error message
 *      is returned.
 *
 * Side effects:
 *      The C variable may be updated to make it consistent with the
 *      Tcl variable, or the Tcl variable may be overwritten to reject
 *      a modification.
 *
 *----------------------------------------------------------------------
 */

static char *
LinkTraceProc(clientData, interp, name1, name2, flags)
    ClientData clientData;      /* Contains information about the link. */
    Tcl_Interp *interp;         /* Interpreter containing Tcl variable. */
    char *name1;                /* First part of variable name. */
    char *name2;                /* Second part of variable name. */
    int flags;                  /* Miscellaneous additional information. */
{
    Link *linkPtr = (Link *) clientData;
    int changed;
    char buffer[TCL_DOUBLE_SPACE];
    char *value, **pp, *result;
    Tcl_Obj *objPtr;

    /*
     * If the variable is being unset, then just re-create it (with a
     * trace) unless the whole interpreter is going away.
     */

    if (flags & TCL_TRACE_UNSETS) {
        if (flags & TCL_INTERP_DESTROYED) {
            ckfree(linkPtr->varName);
            ckfree((char *) linkPtr);
        } else if (flags & TCL_TRACE_DESTROYED) {
            Tcl_SetVar(interp, linkPtr->varName, StringValue(linkPtr, buffer),
                    TCL_GLOBAL_ONLY);
            Tcl_TraceVar(interp, linkPtr->varName, TCL_GLOBAL_ONLY
                    |TCL_TRACE_READS|TCL_TRACE_WRITES|TCL_TRACE_UNSETS,
                    LinkTraceProc, (ClientData) linkPtr);
        }
        return NULL;
    }

    /*
     * If we were invoked because of a call to Tcl_UpdateLinkedVar, then
     * don't do anything at all.  In particular, we don't want to get
     * upset that the variable is being modified, even if it is
     * supposed to be read-only.
     */

    if (linkPtr->flags & LINK_BEING_UPDATED) {
        return NULL;
    }

    /*
     * For read accesses, update the Tcl variable if the C variable
     * has changed since the last time we updated the Tcl variable.
     */

    if (flags & TCL_TRACE_READS) {
        switch (linkPtr->type) {
            case TCL_LINK_INT:
            case TCL_LINK_BOOLEAN:
                changed = *(int *)(linkPtr->addr) != linkPtr->lastValue.i;
                break;
            case TCL_LINK_DOUBLE:
                changed = *(double *)(linkPtr->addr) != linkPtr->lastValue.d;
                break;
            case TCL_LINK_STRING:
                changed = 1;
                break;
            default:
                return "internal error: bad linked variable type";
        }
        if (changed) {
            Tcl_SetVar(interp, linkPtr->varName, StringValue(linkPtr, buffer),
                    TCL_GLOBAL_ONLY);
        }
        return NULL;
    }

    /*
     * For writes, first make sure that the variable is writable.  Then
     * convert the Tcl value to C if possible.  If the variable isn't
     * writable or can't be converted, then restore the varaible's old
     * value and return an error.  Another tricky thing: we have to save
     * and restore the interpreter's result, since the variable access
     * could occur when the result has been partially set.
     */

    if (linkPtr->flags & LINK_READ_ONLY) {
        Tcl_SetVar(interp, linkPtr->varName, StringValue(linkPtr, buffer),
                TCL_GLOBAL_ONLY);
        return "linked variable is read-only";
    }
    value = Tcl_GetVar(interp, linkPtr->varName, TCL_GLOBAL_ONLY);
    if (value == NULL) {
        /*
         * This shouldn't ever happen.
         */
        return "internal error: linked variable couldn't be read";
    }

    objPtr = Tcl_GetObjResult(interp);
    Tcl_IncrRefCount(objPtr);
    Tcl_ResetResult(interp);
    result = NULL;

    switch (linkPtr->type) {
        case TCL_LINK_INT:
            if (Tcl_GetInt(interp, value, &linkPtr->lastValue.i) != TCL_OK) {
                Tcl_SetObjResult(interp, objPtr);
                Tcl_SetVar(interp, linkPtr->varName,
                        StringValue(linkPtr, buffer), TCL_GLOBAL_ONLY);
                result = "variable must have integer value";
                goto end;
            }
            *(int *)(linkPtr->addr) = linkPtr->lastValue.i;
            break;
        case TCL_LINK_DOUBLE:
            if (Tcl_GetDouble(interp, value, &linkPtr->lastValue.d)
                    != TCL_OK) {
                Tcl_SetObjResult(interp, objPtr);
                Tcl_SetVar(interp, linkPtr->varName,
                        StringValue(linkPtr, buffer), TCL_GLOBAL_ONLY);
                result = "variable must have real value";
                goto end;
            }
            *(double *)(linkPtr->addr) = linkPtr->lastValue.d;
            break;
        case TCL_LINK_BOOLEAN:
            if (Tcl_GetBoolean(interp, value, &linkPtr->lastValue.i)
                    != TCL_OK) {
                Tcl_SetObjResult(interp, objPtr);
                Tcl_SetVar(interp, linkPtr->varName,
                        StringValue(linkPtr, buffer), TCL_GLOBAL_ONLY);
                result = "variable must have boolean value";
                goto end;
            }
            *(int *)(linkPtr->addr) = linkPtr->lastValue.i;
            break;
        case TCL_LINK_STRING:
            pp = (char **)(linkPtr->addr);
            if (*pp != NULL) {
                ckfree(*pp);
            }
            *pp = (char *) ckalloc((unsigned) (strlen(value) + 1));
            strcpy(*pp, value);
            break;
        default:
            return "internal error: bad linked variable type";
    }
    end:
    Tcl_DecrRefCount(objPtr);
    return result;
}

/*
 *----------------------------------------------------------------------
 *
 * StringValue --
 *
 *      Converts the value of a C variable to a string for use in a
 *      Tcl variable to which it is linked.
 *
 * Results:
 *      The return value is a pointer to a string that represents
 *      the value of the C variable given by linkPtr.
 *
 * Side effects:
 *      None.
 *
 *----------------------------------------------------------------------
 */

static char *
StringValue(linkPtr, buffer)
    Link *linkPtr;              /* Structure describing linked variable. */
    char *buffer;               /* Small buffer to use for converting
                                 * values.  Must have TCL_DOUBLE_SPACE
                                 * bytes or more. */
{
    char *p;

    switch (linkPtr->type) {
        case TCL_LINK_INT:
            linkPtr->lastValue.i = *(int *)(linkPtr->addr);
            TclFormatInt(buffer, linkPtr->lastValue.i);
            return buffer;
        case TCL_LINK_DOUBLE:
            linkPtr->lastValue.d = *(double *)(linkPtr->addr);
            Tcl_PrintDouble((Tcl_Interp *) NULL, linkPtr->lastValue.d, buffer);
            return buffer;
        case TCL_LINK_BOOLEAN:
            linkPtr->lastValue.i = *(int *)(linkPtr->addr);
            if (linkPtr->lastValue.i != 0) {
                return "1";
            }
            return "0";
        case TCL_LINK_STRING:
            p = *(char **)(linkPtr->addr);
            if (p == NULL) {
                return "NULL";
            }
            return p;
    }

    /*
     * This code only gets executed if the link type is unknown
     * (shouldn't ever happen).
     */

    return "??";
}

/* End of tcllink.c */
1	/* $Header$ */
2	/*
3	* tclLink.c --
4	*
5	* This file implements linked variables (a C variable that is
6	* tied to a Tcl variable). The idea of linked variables was
7	* first suggested by Andreas Stolcke and this implementation is
8	* based heavily on a prototype implementation provided by
9	* him.
10	*
11	* Copyright (c) 1993 The Regents of the University of California.
12	* Copyright (c) 1994-1997 Sun Microsystems, Inc.
13	*
14	* See the file "license.terms" for information on usage and redistribution
15	* of this file, and for a DISCLAIMER OF ALL WARRANTIES.
16	*
17	* RCS: @(#) $Id: tcllink.c,v 1.1.1.1 2001/06/13 04:42:27 dtashley Exp $
18	*/
19
20	#include "tclInt.h"
21
22	/*
23	* For each linked variable there is a data structure of the following
24	* type, which describes the link and is the clientData for the trace
25	* set on the Tcl variable.
26	*/
27
28	typedef struct Link {
29	Tcl_Interp interp; / Interpreter containing Tcl variable. */
30	char varName; / Name of variable (must be global). This
31	* is needed during trace callbacks, since
32	* the actual variable may be aliased at
33	* that time via upvar. */
34	char addr; / Location of C variable. */
35	int type; /* Type of link (TCL_LINK_INT, etc.). */
36	union {
37	int i;
38	double d;
39	} lastValue; /* Last known value of C variable; used to
40	* avoid string conversions. */
41	int flags; /* Miscellaneous one-bit values; see below
42	* for definitions. */
43	} Link;
44
45	/*
46	* Definitions for flag bits:
47	* LINK_READ_ONLY - 1 means errors should be generated if Tcl
48	* script attempts to write variable.
49	* LINK_BEING_UPDATED - 1 means that a call to Tcl_UpdateLinkedVar
50	* is in progress for this variable, so
51	* trace callbacks on the variable should
52	* be ignored.
53	*/
54
55	#define LINK_READ_ONLY 1
56	#define LINK_BEING_UPDATED 2
57
58	/*
59	* Forward references to procedures defined later in this file:
60	*/
61
62	static char * LinkTraceProc _ANSI_ARGS_((ClientData clientData,
63	Tcl_Interp interp, char name1, char *name2,
64	int flags));
65	static char * StringValue _ANSI_ARGS_((Link *linkPtr,
66	char *buffer));
67
68	/*
69	*----------------------------------------------------------------------
70	*
71	* Tcl_LinkVar --
72	*
73	* Link a C variable to a Tcl variable so that changes to either
74	* one causes the other to change.
75	*
76	* Results:
77	* The return value is TCL_OK if everything went well or TCL_ERROR
78	* if an error occurred (the interp's result is also set after
79	* errors).
80	*
81	* Side effects:
82	* The value at *addr is linked to the Tcl variable "varName",
83	* using "type" to convert between string values for Tcl and
84	* binary values for *addr.
85	*
86	*----------------------------------------------------------------------
87	*/
88
89	int
90	Tcl_LinkVar(interp, varName, addr, type)
91	Tcl_Interp interp; / Interpreter in which varName exists. */
92	char varName; / Name of a global variable in interp. */
93	char addr; / Address of a C variable to be linked
94	* to varName. */
95	int type; /* Type of C variable: TCL_LINK_INT, etc.
96	* Also may have TCL_LINK_READ_ONLY
97	* OR'ed in. */
98	{
99	Link *linkPtr;
100	char buffer[TCL_DOUBLE_SPACE];
101	int code;
102
103	linkPtr = (Link *) ckalloc(sizeof(Link));
104	linkPtr->interp = interp;
105	linkPtr->varName = (char *) ckalloc((unsigned) (strlen(varName) + 1));
106	strcpy(linkPtr->varName, varName);
107	linkPtr->addr = addr;
108	linkPtr->type = type & ~TCL_LINK_READ_ONLY;
109	if (type & TCL_LINK_READ_ONLY) {
110	linkPtr->flags = LINK_READ_ONLY;
111	} else {
112	linkPtr->flags = 0;
113	}
114	if (Tcl_SetVar(interp, varName, StringValue(linkPtr, buffer),
115	TCL_GLOBAL_ONLY\|TCL_LEAVE_ERR_MSG) == NULL) {
116	ckfree(linkPtr->varName);
117	ckfree((char *) linkPtr);
118	return TCL_ERROR;
119	}
120	code = Tcl_TraceVar(interp, varName, TCL_GLOBAL_ONLY\|TCL_TRACE_READS
121	\|TCL_TRACE_WRITES\|TCL_TRACE_UNSETS, LinkTraceProc,
122	(ClientData) linkPtr);
123	if (code != TCL_OK) {
124	ckfree(linkPtr->varName);
125	ckfree((char *) linkPtr);
126	}
127	return code;
128	}
129
130	/*
131	*----------------------------------------------------------------------
132	*
133	* Tcl_UnlinkVar --
134	*
135	* Destroy the link between a Tcl variable and a C variable.
136	*
137	* Results:
138	* None.
139	*
140	* Side effects:
141	* If "varName" was previously linked to a C variable, the link
142	* is broken to make the variable independent. If there was no
143	* previous link for "varName" then nothing happens.
144	*
145	*----------------------------------------------------------------------
146	*/
147
148	void
149	Tcl_UnlinkVar(interp, varName)
150	Tcl_Interp interp; / Interpreter containing variable to unlink. */
151	char varName; / Global variable in interp to unlink. */
152	{
153	Link *linkPtr;
154
155	linkPtr = (Link *) Tcl_VarTraceInfo(interp, varName, TCL_GLOBAL_ONLY,
156	LinkTraceProc, (ClientData) NULL);
157	if (linkPtr == NULL) {
158	return;
159	}
160	Tcl_UntraceVar(interp, varName,
161	TCL_GLOBAL_ONLY\|TCL_TRACE_READS\|TCL_TRACE_WRITES\|TCL_TRACE_UNSETS,
162	LinkTraceProc, (ClientData) linkPtr);
163	ckfree(linkPtr->varName);
164	ckfree((char *) linkPtr);
165	}
166
167	/*
168	*----------------------------------------------------------------------
169	*
170	* Tcl_UpdateLinkedVar --
171	*
172	* This procedure is invoked after a linked variable has been
173	* changed by C code. It updates the Tcl variable so that
174	* traces on the variable will trigger.
175	*
176	* Results:
177	* None.
178	*
179	* Side effects:
180	* The Tcl variable "varName" is updated from its C value,
181	* causing traces on the variable to trigger.
182	*
183	*----------------------------------------------------------------------
184	*/
185
186	void
187	Tcl_UpdateLinkedVar(interp, varName)
188	Tcl_Interp interp; / Interpreter containing variable. */
189	char varName; / Name of global variable that is linked. */
190	{
191	Link *linkPtr;
192	char buffer[TCL_DOUBLE_SPACE];
193	int savedFlag;
194
195	linkPtr = (Link *) Tcl_VarTraceInfo(interp, varName, TCL_GLOBAL_ONLY,
196	LinkTraceProc, (ClientData) NULL);
197	if (linkPtr == NULL) {
198	return;
199	}
200	savedFlag = linkPtr->flags & LINK_BEING_UPDATED;
201	linkPtr->flags \|= LINK_BEING_UPDATED;
202	Tcl_SetVar(interp, linkPtr->varName, StringValue(linkPtr, buffer),
203	TCL_GLOBAL_ONLY);
204	linkPtr->flags = (linkPtr->flags & ~LINK_BEING_UPDATED) \| savedFlag;
205	}
206
207	/*
208	*----------------------------------------------------------------------
209	*
210	* LinkTraceProc --
211	*
212	* This procedure is invoked when a linked Tcl variable is read,
213	* written, or unset from Tcl. It's responsible for keeping the
214	* C variable in sync with the Tcl variable.
215	*
216	* Results:
217	* If all goes well, NULL is returned; otherwise an error message
218	* is returned.
219	*
220	* Side effects:
221	* The C variable may be updated to make it consistent with the
222	* Tcl variable, or the Tcl variable may be overwritten to reject
223	* a modification.
224	*
225	*----------------------------------------------------------------------
226	*/
227
228	static char *
229	LinkTraceProc(clientData, interp, name1, name2, flags)
230	ClientData clientData; /* Contains information about the link. */
231	Tcl_Interp interp; / Interpreter containing Tcl variable. */
232	char name1; / First part of variable name. */
233	char name2; / Second part of variable name. */
234	int flags; /* Miscellaneous additional information. */
235	{
236	Link linkPtr = (Link ) clientData;
237	int changed;
238	char buffer[TCL_DOUBLE_SPACE];
239	char value, pp, result;
240	Tcl_Obj *objPtr;
241
242	/*
243	* If the variable is being unset, then just re-create it (with a
244	* trace) unless the whole interpreter is going away.
245	*/
246
247	if (flags & TCL_TRACE_UNSETS) {
248	if (flags & TCL_INTERP_DESTROYED) {
249	ckfree(linkPtr->varName);
250	ckfree((char *) linkPtr);
251	} else if (flags & TCL_TRACE_DESTROYED) {
252	Tcl_SetVar(interp, linkPtr->varName, StringValue(linkPtr, buffer),
253	TCL_GLOBAL_ONLY);
254	Tcl_TraceVar(interp, linkPtr->varName, TCL_GLOBAL_ONLY
255	\|TCL_TRACE_READS\|TCL_TRACE_WRITES\|TCL_TRACE_UNSETS,
256	LinkTraceProc, (ClientData) linkPtr);
257	}
258	return NULL;
259	}
260
261	/*
262	* If we were invoked because of a call to Tcl_UpdateLinkedVar, then
263	* don't do anything at all. In particular, we don't want to get
264	* upset that the variable is being modified, even if it is
265	* supposed to be read-only.
266	*/
267
268	if (linkPtr->flags & LINK_BEING_UPDATED) {
269	return NULL;
270	}
271
272	/*
273	* For read accesses, update the Tcl variable if the C variable
274	* has changed since the last time we updated the Tcl variable.
275	*/
276
277	if (flags & TCL_TRACE_READS) {
278	switch (linkPtr->type) {
279	case TCL_LINK_INT:
280	case TCL_LINK_BOOLEAN:
281	changed = (int )(linkPtr->addr) != linkPtr->lastValue.i;
282	break;
283	case TCL_LINK_DOUBLE:
284	changed = (double )(linkPtr->addr) != linkPtr->lastValue.d;
285	break;
286	case TCL_LINK_STRING:
287	changed = 1;
288	break;
289	default:
290	return "internal error: bad linked variable type";
291	}
292	if (changed) {
293	Tcl_SetVar(interp, linkPtr->varName, StringValue(linkPtr, buffer),
294	TCL_GLOBAL_ONLY);
295	}
296	return NULL;
297	}
298
299	/*
300	* For writes, first make sure that the variable is writable. Then
301	* convert the Tcl value to C if possible. If the variable isn't
302	* writable or can't be converted, then restore the varaible's old
303	* value and return an error. Another tricky thing: we have to save
304	* and restore the interpreter's result, since the variable access
305	* could occur when the result has been partially set.
306	*/
307
308	if (linkPtr->flags & LINK_READ_ONLY) {
309	Tcl_SetVar(interp, linkPtr->varName, StringValue(linkPtr, buffer),
310	TCL_GLOBAL_ONLY);
311	return "linked variable is read-only";
312	}
313	value = Tcl_GetVar(interp, linkPtr->varName, TCL_GLOBAL_ONLY);
314	if (value == NULL) {
315	/*
316	* This shouldn't ever happen.
317	*/
318	return "internal error: linked variable couldn't be read";
319	}
320
321	objPtr = Tcl_GetObjResult(interp);
322	Tcl_IncrRefCount(objPtr);
323	Tcl_ResetResult(interp);
324	result = NULL;
325
326	switch (linkPtr->type) {
327	case TCL_LINK_INT:
328	if (Tcl_GetInt(interp, value, &linkPtr->lastValue.i) != TCL_OK) {
329	Tcl_SetObjResult(interp, objPtr);
330	Tcl_SetVar(interp, linkPtr->varName,
331	StringValue(linkPtr, buffer), TCL_GLOBAL_ONLY);
332	result = "variable must have integer value";
333	goto end;
334	}
335	(int )(linkPtr->addr) = linkPtr->lastValue.i;
336	break;
337	case TCL_LINK_DOUBLE:
338	if (Tcl_GetDouble(interp, value, &linkPtr->lastValue.d)
339	!= TCL_OK) {
340	Tcl_SetObjResult(interp, objPtr);
341	Tcl_SetVar(interp, linkPtr->varName,
342	StringValue(linkPtr, buffer), TCL_GLOBAL_ONLY);
343	result = "variable must have real value";
344	goto end;
345	}
346	(double )(linkPtr->addr) = linkPtr->lastValue.d;
347	break;
348	case TCL_LINK_BOOLEAN:
349	if (Tcl_GetBoolean(interp, value, &linkPtr->lastValue.i)
350	!= TCL_OK) {
351	Tcl_SetObjResult(interp, objPtr);
352	Tcl_SetVar(interp, linkPtr->varName,
353	StringValue(linkPtr, buffer), TCL_GLOBAL_ONLY);
354	result = "variable must have boolean value";
355	goto end;
356	}
357	(int )(linkPtr->addr) = linkPtr->lastValue.i;
358	break;
359	case TCL_LINK_STRING:
360	pp = (char **)(linkPtr->addr);
361	if (*pp != NULL) {
362	ckfree(*pp);
363	}
364	pp = (char ) ckalloc((unsigned) (strlen(value) + 1));
365	strcpy(*pp, value);
366	break;
367	default:
368	return "internal error: bad linked variable type";
369	}
370	end:
371	Tcl_DecrRefCount(objPtr);
372	return result;
373	}
374
375	/*
376	*----------------------------------------------------------------------
377	*
378	* StringValue --
379	*
380	* Converts the value of a C variable to a string for use in a
381	* Tcl variable to which it is linked.
382	*
383	* Results:
384	* The return value is a pointer to a string that represents
385	* the value of the C variable given by linkPtr.
386	*
387	* Side effects:
388	* None.
389	*
390	*----------------------------------------------------------------------
391	*/
392
393	static char *
394	StringValue(linkPtr, buffer)
395	Link linkPtr; / Structure describing linked variable. */
396	char buffer; / Small buffer to use for converting
397	* values. Must have TCL_DOUBLE_SPACE
398	* bytes or more. */
399	{
400	char *p;
401
402	switch (linkPtr->type) {
403	case TCL_LINK_INT:
404	linkPtr->lastValue.i = (int )(linkPtr->addr);
405	TclFormatInt(buffer, linkPtr->lastValue.i);
406	return buffer;
407	case TCL_LINK_DOUBLE:
408	linkPtr->lastValue.d = (double )(linkPtr->addr);
409	Tcl_PrintDouble((Tcl_Interp *) NULL, linkPtr->lastValue.d, buffer);
410	return buffer;
411	case TCL_LINK_BOOLEAN:
412	linkPtr->lastValue.i = (int )(linkPtr->addr);
413	if (linkPtr->lastValue.i != 0) {
414	return "1";
415	}
416	return "0";
417	case TCL_LINK_STRING:
418	p = (char *)(linkPtr->addr);
419	if (p == NULL) {
420	return "NULL";
421	}
422	return p;
423	}
424
425	/*
426	* This code only gets executed if the link type is unknown
427	* (shouldn't ever happen).
428	*/
429
430	return "??";
431	}
432
433	/* End of tcllink.c */