1 | /* |
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2 | * tclLink.c -- |
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3 | * |
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4 | * This file implements linked variables (a C variable that is |
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5 | * tied to a Tcl variable). The idea of linked variables was |
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6 | * first suggested by Andreas Stolcke and this implementation is |
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7 | * based heavily on a prototype implementation provided by |
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8 | * him. |
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9 | * |
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10 | * Copyright (c) 1993 The Regents of the University of California. |
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11 | * Copyright (c) 1994-1996 Sun Microsystems, Inc. |
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12 | * |
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13 | * See the file "license.terms" for information on usage and redistribution |
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14 | * of this file, and for a DISCLAIMER OF ALL WARRANTIES. |
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15 | * |
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16 | * RCS: @(#) $Id: tclLink.c,v 1.1 2008-06-04 13:58:07 demin Exp $ |
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17 | */ |
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18 | |
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19 | #include "tclInt.h" |
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20 | |
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21 | /* |
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22 | * For each linked variable there is a data structure of the following |
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23 | * type, which describes the link and is the clientData for the trace |
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24 | * set on the Tcl variable. |
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25 | */ |
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26 | |
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27 | typedef struct Link { |
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28 | Tcl_Interp *interp; /* Interpreter containing Tcl variable. */ |
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29 | char *varName; /* Name of variable (must be global). This |
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30 | * is needed during trace callbacks, since |
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31 | * the actual variable may be aliased at |
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32 | * that time via upvar. */ |
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33 | char *addr; /* Location of C variable. */ |
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34 | int type; /* Type of link (TCL_LINK_INT, etc.). */ |
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35 | union { |
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36 | int i; |
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37 | double d; |
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38 | } lastValue; /* Last known value of C variable; used to |
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39 | * avoid string conversions. */ |
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40 | int flags; /* Miscellaneous one-bit values; see below |
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41 | * for definitions. */ |
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42 | } Link; |
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43 | |
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44 | /* |
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45 | * Definitions for flag bits: |
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46 | * LINK_READ_ONLY - 1 means errors should be generated if Tcl |
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47 | * script attempts to write variable. |
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48 | * LINK_BEING_UPDATED - 1 means that a call to Tcl_UpdateLinkedVar |
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49 | * is in progress for this variable, so |
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50 | * trace callbacks on the variable should |
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51 | * be ignored. |
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52 | */ |
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53 | |
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54 | #define LINK_READ_ONLY 1 |
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55 | #define LINK_BEING_UPDATED 2 |
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56 | |
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57 | /* |
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58 | * Forward references to procedures defined later in this file: |
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59 | */ |
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60 | |
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61 | static char * LinkTraceProc _ANSI_ARGS_((ClientData clientData, |
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62 | Tcl_Interp *interp, char *name1, char *name2, |
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63 | int flags)); |
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64 | static char * StringValue _ANSI_ARGS_((Link *linkPtr, |
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65 | char *buffer)); |
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66 | |
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67 | /* |
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68 | *---------------------------------------------------------------------- |
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69 | * |
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70 | * Tcl_LinkVar -- |
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71 | * |
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72 | * Link a C variable to a Tcl variable so that changes to either |
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73 | * one causes the other to change. |
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74 | * |
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75 | * Results: |
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76 | * The return value is TCL_OK if everything went well or TCL_ERROR |
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77 | * if an error occurred (interp->result is also set after errors). |
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78 | * |
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79 | * Side effects: |
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80 | * The value at *addr is linked to the Tcl variable "varName", |
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81 | * using "type" to convert between string values for Tcl and |
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82 | * binary values for *addr. |
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83 | * |
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84 | *---------------------------------------------------------------------- |
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85 | */ |
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86 | |
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87 | int |
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88 | Tcl_LinkVar(interp, varName, addr, type) |
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89 | Tcl_Interp *interp; /* Interpreter in which varName exists. */ |
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90 | char *varName; /* Name of a global variable in interp. */ |
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91 | char *addr; /* Address of a C variable to be linked |
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92 | * to varName. */ |
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93 | int type; /* Type of C variable: TCL_LINK_INT, etc. |
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94 | * Also may have TCL_LINK_READ_ONLY |
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95 | * OR'ed in. */ |
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96 | { |
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97 | Link *linkPtr; |
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98 | char buffer[TCL_DOUBLE_SPACE]; |
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99 | int code; |
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100 | |
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101 | linkPtr = (Link *) ckalloc(sizeof(Link)); |
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102 | linkPtr->interp = interp; |
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103 | linkPtr->varName = (char *) ckalloc((unsigned) (strlen(varName) + 1)); |
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104 | strcpy(linkPtr->varName, varName); |
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105 | linkPtr->addr = addr; |
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106 | linkPtr->type = type & ~TCL_LINK_READ_ONLY; |
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107 | if (type & TCL_LINK_READ_ONLY) { |
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108 | linkPtr->flags = LINK_READ_ONLY; |
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109 | } else { |
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110 | linkPtr->flags = 0; |
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111 | } |
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112 | if (Tcl_SetVar(interp, varName, StringValue(linkPtr, buffer), |
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113 | TCL_GLOBAL_ONLY|TCL_LEAVE_ERR_MSG) == NULL) { |
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114 | ckfree(linkPtr->varName); |
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115 | ckfree((char *) linkPtr); |
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116 | return TCL_ERROR; |
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117 | } |
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118 | code = Tcl_TraceVar(interp, varName, TCL_GLOBAL_ONLY|TCL_TRACE_READS |
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119 | |TCL_TRACE_WRITES|TCL_TRACE_UNSETS, LinkTraceProc, |
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120 | (ClientData) linkPtr); |
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121 | if (code != TCL_OK) { |
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122 | ckfree(linkPtr->varName); |
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123 | ckfree((char *) linkPtr); |
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124 | } |
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125 | return code; |
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126 | } |
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127 | |
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128 | /* |
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129 | *---------------------------------------------------------------------- |
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130 | * |
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131 | * Tcl_UnlinkVar -- |
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132 | * |
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133 | * Destroy the link between a Tcl variable and a C variable. |
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134 | * |
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135 | * Results: |
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136 | * None. |
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137 | * |
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138 | * Side effects: |
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139 | * If "varName" was previously linked to a C variable, the link |
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140 | * is broken to make the variable independent. If there was no |
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141 | * previous link for "varName" then nothing happens. |
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142 | * |
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143 | *---------------------------------------------------------------------- |
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144 | */ |
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145 | |
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146 | void |
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147 | Tcl_UnlinkVar(interp, varName) |
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148 | Tcl_Interp *interp; /* Interpreter containing variable to unlink. */ |
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149 | char *varName; /* Global variable in interp to unlink. */ |
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150 | { |
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151 | Link *linkPtr; |
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152 | |
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153 | linkPtr = (Link *) Tcl_VarTraceInfo(interp, varName, TCL_GLOBAL_ONLY, |
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154 | LinkTraceProc, (ClientData) NULL); |
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155 | if (linkPtr == NULL) { |
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156 | return; |
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157 | } |
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158 | Tcl_UntraceVar(interp, varName, |
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159 | TCL_GLOBAL_ONLY|TCL_TRACE_READS|TCL_TRACE_WRITES|TCL_TRACE_UNSETS, |
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160 | LinkTraceProc, (ClientData) linkPtr); |
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161 | ckfree(linkPtr->varName); |
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162 | ckfree((char *) linkPtr); |
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163 | } |
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164 | |
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165 | /* |
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166 | *---------------------------------------------------------------------- |
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167 | * |
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168 | * Tcl_UpdateLinkedVar -- |
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169 | * |
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170 | * This procedure is invoked after a linked variable has been |
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171 | * changed by C code. It updates the Tcl variable so that |
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172 | * traces on the variable will trigger. |
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173 | * |
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174 | * Results: |
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175 | * None. |
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176 | * |
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177 | * Side effects: |
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178 | * The Tcl variable "varName" is updated from its C value, |
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179 | * causing traces on the variable to trigger. |
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180 | * |
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181 | *---------------------------------------------------------------------- |
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182 | */ |
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183 | |
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184 | void |
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185 | Tcl_UpdateLinkedVar(interp, varName) |
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186 | Tcl_Interp *interp; /* Interpreter containing variable. */ |
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187 | char *varName; /* Name of global variable that is linked. */ |
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188 | { |
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189 | Link *linkPtr; |
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190 | char buffer[TCL_DOUBLE_SPACE]; |
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191 | int savedFlag; |
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192 | |
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193 | linkPtr = (Link *) Tcl_VarTraceInfo(interp, varName, TCL_GLOBAL_ONLY, |
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194 | LinkTraceProc, (ClientData) NULL); |
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195 | if (linkPtr == NULL) { |
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196 | return; |
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197 | } |
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198 | savedFlag = linkPtr->flags & LINK_BEING_UPDATED; |
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199 | linkPtr->flags |= LINK_BEING_UPDATED; |
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200 | Tcl_SetVar(interp, linkPtr->varName, StringValue(linkPtr, buffer), |
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201 | TCL_GLOBAL_ONLY); |
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202 | linkPtr->flags = (linkPtr->flags & ~LINK_BEING_UPDATED) | savedFlag; |
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203 | } |
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204 | |
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205 | /* |
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206 | *---------------------------------------------------------------------- |
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207 | * |
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208 | * LinkTraceProc -- |
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209 | * |
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210 | * This procedure is invoked when a linked Tcl variable is read, |
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211 | * written, or unset from Tcl. It's responsible for keeping the |
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212 | * C variable in sync with the Tcl variable. |
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213 | * |
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214 | * Results: |
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215 | * If all goes well, NULL is returned; otherwise an error message |
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216 | * is returned. |
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217 | * |
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218 | * Side effects: |
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219 | * The C variable may be updated to make it consistent with the |
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220 | * Tcl variable, or the Tcl variable may be overwritten to reject |
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221 | * a modification. |
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222 | * |
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223 | *---------------------------------------------------------------------- |
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224 | */ |
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225 | |
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226 | static char * |
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227 | LinkTraceProc(clientData, interp, name1, name2, flags) |
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228 | ClientData clientData; /* Contains information about the link. */ |
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229 | Tcl_Interp *interp; /* Interpreter containing Tcl variable. */ |
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230 | char *name1; /* First part of variable name. */ |
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231 | char *name2; /* Second part of variable name. */ |
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232 | int flags; /* Miscellaneous additional information. */ |
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233 | { |
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234 | Link *linkPtr = (Link *) clientData; |
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235 | int changed; |
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236 | char buffer[TCL_DOUBLE_SPACE]; |
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237 | char *value, **pp; |
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238 | Tcl_DString savedResult; |
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239 | |
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240 | /* |
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241 | * If the variable is being unset, then just re-create it (with a |
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242 | * trace) unless the whole interpreter is going away. |
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243 | */ |
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244 | |
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245 | if (flags & TCL_TRACE_UNSETS) { |
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246 | if (flags & TCL_INTERP_DESTROYED) { |
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247 | ckfree(linkPtr->varName); |
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248 | ckfree((char *) linkPtr); |
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249 | } else if (flags & TCL_TRACE_DESTROYED) { |
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250 | Tcl_SetVar(interp, linkPtr->varName, StringValue(linkPtr, buffer), |
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251 | TCL_GLOBAL_ONLY); |
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252 | Tcl_TraceVar(interp, linkPtr->varName, TCL_GLOBAL_ONLY |
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253 | |TCL_TRACE_READS|TCL_TRACE_WRITES|TCL_TRACE_UNSETS, |
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254 | LinkTraceProc, (ClientData) linkPtr); |
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255 | } |
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256 | return NULL; |
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257 | } |
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258 | |
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259 | /* |
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260 | * If we were invoked because of a call to Tcl_UpdateLinkedVar, then |
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261 | * don't do anything at all. In particular, we don't want to get |
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262 | * upset that the variable is being modified, even if it is |
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263 | * supposed to be read-only. |
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264 | */ |
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265 | |
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266 | if (linkPtr->flags & LINK_BEING_UPDATED) { |
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267 | return NULL; |
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268 | } |
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269 | |
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270 | /* |
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271 | * For read accesses, update the Tcl variable if the C variable |
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272 | * has changed since the last time we updated the Tcl variable. |
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273 | */ |
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274 | |
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275 | if (flags & TCL_TRACE_READS) { |
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276 | switch (linkPtr->type) { |
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277 | case TCL_LINK_INT: |
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278 | case TCL_LINK_BOOLEAN: |
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279 | changed = *(int *)(linkPtr->addr) != linkPtr->lastValue.i; |
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280 | break; |
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281 | case TCL_LINK_DOUBLE: |
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282 | changed = *(double *)(linkPtr->addr) != linkPtr->lastValue.d; |
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283 | break; |
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284 | case TCL_LINK_STRING: |
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285 | changed = 1; |
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286 | break; |
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287 | default: |
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288 | return "internal error: bad linked variable type"; |
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289 | } |
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290 | if (changed) { |
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291 | Tcl_SetVar(interp, linkPtr->varName, StringValue(linkPtr, buffer), |
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292 | TCL_GLOBAL_ONLY); |
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293 | } |
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294 | return NULL; |
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295 | } |
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296 | |
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297 | /* |
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298 | * For writes, first make sure that the variable is writable. Then |
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299 | * convert the Tcl value to C if possible. If the variable isn't |
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300 | * writable or can't be converted, then restore the varaible's old |
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301 | * value and return an error. Another tricky thing: we have to save |
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302 | * and restore the interpreter's result, since the variable access |
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303 | * could occur when the result has been partially set. |
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304 | */ |
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305 | |
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306 | if (linkPtr->flags & LINK_READ_ONLY) { |
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307 | Tcl_SetVar(interp, linkPtr->varName, StringValue(linkPtr, buffer), |
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308 | TCL_GLOBAL_ONLY); |
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309 | return "linked variable is read-only"; |
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310 | } |
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311 | value = Tcl_GetVar(interp, linkPtr->varName, TCL_GLOBAL_ONLY); |
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312 | if (value == NULL) { |
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313 | /* |
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314 | * This shouldn't ever happen. |
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315 | */ |
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316 | return "internal error: linked variable couldn't be read"; |
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317 | } |
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318 | Tcl_DStringInit(&savedResult); |
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319 | Tcl_DStringAppend(&savedResult, interp->result, -1); |
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320 | Tcl_ResetResult(interp); |
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321 | switch (linkPtr->type) { |
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322 | case TCL_LINK_INT: |
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323 | if (Tcl_GetInt(interp, value, &linkPtr->lastValue.i) != TCL_OK) { |
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324 | Tcl_DStringResult(interp, &savedResult); |
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325 | Tcl_SetVar(interp, linkPtr->varName, |
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326 | StringValue(linkPtr, buffer), TCL_GLOBAL_ONLY); |
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327 | return "variable must have integer value"; |
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328 | } |
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329 | *(int *)(linkPtr->addr) = linkPtr->lastValue.i; |
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330 | break; |
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331 | case TCL_LINK_DOUBLE: |
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332 | if (Tcl_GetDouble(interp, value, &linkPtr->lastValue.d) |
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333 | != TCL_OK) { |
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334 | Tcl_DStringResult(interp, &savedResult); |
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335 | Tcl_SetVar(interp, linkPtr->varName, |
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336 | StringValue(linkPtr, buffer), TCL_GLOBAL_ONLY); |
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337 | return "variable must have real value"; |
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338 | } |
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339 | *(double *)(linkPtr->addr) = linkPtr->lastValue.d; |
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340 | break; |
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341 | case TCL_LINK_BOOLEAN: |
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342 | if (Tcl_GetBoolean(interp, value, &linkPtr->lastValue.i) |
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343 | != TCL_OK) { |
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344 | Tcl_DStringResult(interp, &savedResult); |
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345 | Tcl_SetVar(interp, linkPtr->varName, |
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346 | StringValue(linkPtr, buffer), TCL_GLOBAL_ONLY); |
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347 | return "variable must have boolean value"; |
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348 | } |
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349 | *(int *)(linkPtr->addr) = linkPtr->lastValue.i; |
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350 | break; |
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351 | case TCL_LINK_STRING: |
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352 | pp = (char **)(linkPtr->addr); |
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353 | if (*pp != NULL) { |
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354 | ckfree(*pp); |
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355 | } |
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356 | *pp = (char *) ckalloc((unsigned) (strlen(value) + 1)); |
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357 | strcpy(*pp, value); |
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358 | break; |
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359 | default: |
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360 | return "internal error: bad linked variable type"; |
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361 | } |
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362 | Tcl_DStringResult(interp, &savedResult); |
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363 | return NULL; |
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364 | } |
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365 | |
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366 | /* |
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367 | *---------------------------------------------------------------------- |
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368 | * |
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369 | * StringValue -- |
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370 | * |
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371 | * Converts the value of a C variable to a string for use in a |
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372 | * Tcl variable to which it is linked. |
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373 | * |
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374 | * Results: |
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375 | * The return value is a pointer |
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376 | to a string that represents |
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377 | * the value of the C variable given by linkPtr. |
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378 | * |
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379 | * Side effects: |
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380 | * None. |
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381 | * |
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382 | *---------------------------------------------------------------------- |
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383 | */ |
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384 | |
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385 | static char * |
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386 | StringValue(linkPtr, buffer) |
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387 | Link *linkPtr; /* Structure describing linked variable. */ |
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388 | char *buffer; /* Small buffer to use for converting |
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389 | * values. Must have TCL_DOUBLE_SPACE |
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390 | * bytes or more. */ |
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391 | { |
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392 | char *p; |
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393 | |
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394 | switch (linkPtr->type) { |
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395 | case TCL_LINK_INT: |
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396 | linkPtr->lastValue.i = *(int *)(linkPtr->addr); |
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397 | TclFormatInt(buffer, linkPtr->lastValue.i); |
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398 | return buffer; |
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399 | case TCL_LINK_DOUBLE: |
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400 | linkPtr->lastValue.d = *(double *)(linkPtr->addr); |
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401 | Tcl_PrintDouble((Tcl_Interp *) NULL, linkPtr->lastValue.d, buffer); |
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402 | return buffer; |
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403 | case TCL_LINK_BOOLEAN: |
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404 | linkPtr->lastValue.i = *(int *)(linkPtr->addr); |
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405 | if (linkPtr->lastValue.i != 0) { |
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406 | return "1"; |
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407 | } |
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408 | return "0"; |
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409 | case TCL_LINK_STRING: |
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410 | p = *(char **)(linkPtr->addr); |
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411 | if (p == NULL) { |
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412 | return "NULL"; |
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413 | } |
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414 | return p; |
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415 | } |
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416 | |
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417 | /* |
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418 | * This code only gets executed if the link type is unknown |
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419 | * (shouldn't ever happen). |
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420 | */ |
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421 | |
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422 | return "??"; |
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423 | } |
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