If an options that requires a value is found but the value is not, then optname will contain a: and OPTARG will contain the name of the option whose argument is missing.
如果发现一个选项需要值，但是找不到这个值，则optname将包含一个：而OPTARG将包含丢失参数的选项的名称。
If an options that requires a value is found but the value is not, then optname will contain a: and OPTARG will contain the name of the option whose argument is missing.
如果发现一个选项需要值，但是找不到这个值，则optname将包含一个：而OPTARG将包含丢失参数的选项的名称。
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