This namespace declaration is required for any application that USES the library since the user-defined function has to be in a certain namespace.

任何使用该库的应用程序都需要这个名称空间声明，因为用户定义的函数必须存在某个名称空间中。

youdao

Defaults to 20 if not explicitly defined by the user before inclusion of the first library header.

如果在首次包含本库头文件之前用户未显式定义该宏，则缺省为20。

youdao

WebSphere Portal Server allows developers to implement and provide a user-defined customized tag library.

WebSphere Portal Server允许开发者实现和提供用户定义的定制标记库。

youdao

It's defined in CS50's library; its sole purpose in life is to ask the user for a floating point value and return it.

它被定义在CS50的函数库中，它的唯一目的是,向用户询问一个浮点数的值，然后返回它。

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