The Book class is then defined, with private member variables for each field.

然后定义book类，用私有成员变量代表每个字段。

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That is, in C++, objects of the same class cannot see one another's private member variables.

也就是说，在 C++ 中，同一个类的对象无法看到彼此的私有成员变量。

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In the same vein, assert is also used to test the internal state of a function-such as private member variables, or variables with internal linkage used strictly within the file.

同理，断言也被用来测试函数的内部状态，比如说私有成员变量或者文件的内部变量(variables with inner - linkage used strictly within the file .)。

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