C ++搞砸了:可选参数强制为强制性

问题描述：

我想要一个带有可选参数的函数.但是，VC ++引发了我无法理解的错误.代码很简单，如下所示:

I want to have a function with optional argument. However, VC++ is throwing an error I cannot comprehend. The code is as simple as follows:

#include <iostream>
#include <iomanip>
#include <string>
using namespace std;

void myFunction(string something, int w);

int main()
{
    myFunction("a string");

    int a = 1;
}

void myFunction(string something, int w = 5)
{
    cout << something << " - " << w << endl;
}

它抱怨:

'myFunction': function does not take 1 arguments

但是，如果我将myFunction()移到main()之前，则不会出错.到底是怎么回事?请帮忙.谢谢.

However if I move myFunction() before main(), it gives no error. What is going on? Please help. Thank you.

答

此错误是因为调用函数时有可选变量，但声明中没有.

This error is because you have optional variables when you call your function, but not in your declaration.

这将创建一个具有两个变量的函数:

This will create a function with two variables:

void myFunction(string something, int w);

但是，这会使第二个变量成为可选变量:

However, this would make the second variable optional:

void myFunction(string something, int w=5);

您需要使声明具有可选变量.

You need to make the declaration have a optional variable.

此外，令您惊讶的是，您的编译器没有尝试吐出与重新定义有关的某种错误. (~~甚至可能是编译器错误！我将对此进行最新研究.~~ 更新:似乎不是编译器错误，但绝对是我很想拥有的功能.即使是错误，也可能与 linker 相关.)

Also, I am surprised your compiler didn't try to spit some sort of error relating to a redefinition. (~~That might even be a compiler bug! I will update on research into this.~~ Update: Doesn't seem like compiler bug, but definitely a feature I would love to have. Even if it was a bug, it would be linker related.)

C ++搞砸了:可选参数强制为强制性

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