这是一个逗号操作符。

This is the comma operator.

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避免使用逗号操作符，除非在特定的for语句的控制部分。

Avoid the use of the comma operator except for very disciplined use in the control part of for statements.

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逗号操作符(如本小节)中描述不能出现在上下文中使用逗号分隔列表中的条目(如参数初始化函数或列表)。

The comma operator (as described in this subclause) cannot appear in contexts where a comma is used to separate items in a list (such as arguments to functions or lists of initializers).

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