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今天改了一段Tcl代码,一段非常复杂的非常长的swith代码,总是遇到这样一个奇怪的错误:
"extra switch pattern with no body, this may be due to a comment incorrectly placed outside of a switch body - see the "switch" documentation"
于是我检查{}是否匹配,检查entry写的是否正确,检查switch的变量是否正确……反复几遍之后,错误仍然在,几近崩溃。
Google了半天,也没找到解决方法。
最终还是抱着试试看的心态打开了Tcl/Tk经典书《Practical Programming in Tcl and Tk》,打开第六章第二节,发现本节结束处赫然写着这样一段话:
A comment can occur only where the Tcl parser expects a command to begin. This restricts the location of comments in a switch command. You must put them inside the command body associated with a pattern, as shown in . If you put a comment at the same level as the patterns, the switch command will try to interpret the comment as one or more pattern-body pairs.
该示例如下:
Example 6-6 Comments in switch commandsswitch -- $value { # this comment confuses switch pattern { # this comment is ok }}
我赶紧查看了一下我的代码,发现有好几个处“} ;#end of XXX”这样的注释。把它们去掉之后,就可以正常work了。
下面就是带有错误注释的不能工作的代码段。
append C(HostMMCAP) ",$ap" # Record this reservd AP append MMCAPRSVD " $ap" } ;# end of if } else { AlertBox warn /"You can NOT reserve it! This AP has been reserved by $rsv_login in $rsv_site with COOL session (COOLID) $rsv_id.Please contact user /"$rsv_login/" if you really want to use it." set MMCAPDISPLAY($ap) 0 return } ;# end of else } ;# end of entry "reserved"
由此得知,虽然“;#”这样的注释在Tcl中一般是很常见的,但是在switch中语句中是不能用的,只能在单独一行里写注释。
以此文为记。
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