函数参数默认值
1.
int Add (int a, int b = 3);
int Add (int a, int b)
{
}
2.
int Add (int a, int b);
int Add (int a, int b = 3)
{
}
两者都有效；这是标准方式，为什么?
Both work; which is the standard way and why?
推荐答案
如果你把声明放在一个头文件中，而定义在一个单独的 .cpp 文件中，并且 #include 来自不同 .cpp 文件的标题，您将能够看到差异.
If you put the declaration in a header file, and the definition in a separate .cpp file, and #include the header from a different .cpp file, you will be able to see the difference.
具体来说，假设:
int Add(int a, int b);
lib.cpp
int Add(int a, int b = 3) {
...
}
test.cpp
#include "lib.h"
int main() {
Add(4);
}
test.cpp的编译不会看到默认的参数声明，会报错.
The compilation of test.cpp will not see the default parameter declaration, and will fail with an error.
为此，默认参数定义通常在函数声明中指定:
For this reason, the default parameter definition is usually specified in the function declaration:
int Add(int a, int b = 3);
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