August 2021
Intermediate to advanced
450 pages
5h 35m
Chinese
Content preview from C++语言导学（原书第2版）
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3.6.1 参数传递
首先考虑如何将值传入函数。默认是拷贝方式（“传值”），如果我们希望在调用者的环境中引用一个对象，则可采用引用方式（“传引用”）。例如：
当关注性能时，我们通常采用传值方式传递小对象，用传引用方式传递大对象。这里“小”的含义是指“拷贝代价确实很低的东西”。“小”的准确含义依赖于机器架构，但“两三个指针大小或更小”是一条很好的经验法则。
如果基于性能原因想采用传引用方式，但又不希望修改实参，则可采用传const引用的方式，就像sum（）例子中那样。这是目前为止普通程序代码中最常见的情况：这种参数传递方式又快又不易出错。
函数参数具有默认值是很常见的，即一个值被认为是首选的或是最常见的。我们可以采用默认函数参数（default function argument）来指定这样一个默认值。例如：
它是重载的一种替代，符号上更为简单：
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