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<pre>
<code style="font-family: Courier New, Courier, monospace; font-size: 12">
#!/usr/bin/tclsh
#
# Demonstrate Data Structures
# using procedural wrappers
 
proc UserAdd { Acct rName eMail phone } {
  global uData

  if {[info exists uData($Acct,rname)]} {
    return 1
    }
  set uData($Acct,rname) $rName
  set uData($Acct,email) $eMail
  set uData($Acct,phone) $phone
  return 0
}
 
puts stdout [UserAdd bpb\
  Brian [e-mail] 555-1212]
 
puts stdout [UserAdd tom\
  Tom [e-mail] 555-1212]
 
puts stdout [UserAdd bpb\
  Brian [e-mail] 555-1212]
  
******
~/tcltk$ <b>./datas.tcl</b>
0
0
1
			</code>
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<td width="90%"><font size="4" face="Verdana, Arial, Helvetica"><b>Data structures in Tcl</b></font></td><td width="200" align="right"><font size="1" face="Verdana, Arial, Helvetica"><nobr>   第 12 页（共15 页）</nobr></font></td>
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<p>Beyond simple multi-dimensional arrays, it is generally recommended that Tcl data structures be implemented as arrays that have dedicated procedural interfaces. This design hides specific implementation details from the user of the structures, while providing the ability to perform significant error checking capabilities.</p>
<p>In the example at left, after declaring <i>uData</i> as a global variable, the code executes a check to see that the account doesn't already exist. If it does, then the procedure returns with a (non-zero) error message. The return can be used in a switch to generate error text output. For the example, we simply feed it three sequential inputs, including one repeat. This yields the output shown at the bottom, with the '1' indicating a purposeful error return due to a repeating account name.</p>
<p>Other possibilities for data structures include lists of arrays, linked or doubly-linked arrays, or various permutations thereof. The lists of arrays construct are considerably more efficient with the list reimplementation that accompanied Tcl 8.0, providing constant access times.</p>
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