The first time around, the templated version of f is called, with a string as the first argument type, and the character and double are packed off as the variable size argument.

首先调用 f 的模板化版本，第一个参数的类型是字符串，作为大小可变的参数提供字符和双精度值。

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Variable-length character string having maximum length size bytes or characters.

具有最大长度的带有字符集属性的可变长度的字符类型。

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