收到 C2628 错误

Question

考虑以下代码：

#include<iostream>
using namespace std;
class sample
{
    int a;
    int b;
public:
    void setValue()
    {
        a=25;
        b=40;
    }
    friend float mean(sample s)
    {
        return float(s.a+s.b)/2.0;
    }
}
int main()
{
    sample x;

    x.setValue();
    cout<< "mean value:"<< mean(x)<<endl;

    cin.ignore();
    getchar();
    return (0);
}

我希望在尝试编译和运行它时输出：

平均值：32.5

但是，我得到了这些编译器错误：

1>  frndF.cpp
1>c:\users\mg\documents\visual studio 2010\projects\frndf\frndf\frndf.cpp(18): error C2628: 'sample' followed by 'int' is illegal (did you forget a ';'?)
1>c:\users\mg\documents\visual studio 2010\projects\frndf\frndf\frndf.cpp(19): error C3874: return type of 'main' should be 'int' instead of 'sample'
1>c:\users\mg\documents\visual studio 2010\projects\frndf\frndf\frndf.cpp(27): error C2664: 'sample::sample(const sample &)' : cannot convert parameter 1 from 'int' to 'const sample &'
1>          Reason: cannot convert from 'int' to 'const sample'
1>          No constructor could take the source type, or constructor overload resolution was ambiguous
1>c:\users\mg\documents\visual studio 2010\projects\frndf\frndf\frndf.cpp(15): warning C4244: 'return' : conversion from 'double' to 'float', possible loss of data

我做错了什么？

Answer 1

您忘记了类定义的右括号后的分号：

class sample
{
   //code omitted for brevity

}; <------------------- you forgot this

虽然，这与错误或预期输出无关，但您应该将参数传递给mean()按const引用：

friend float mean(sample const & s)
{                      //^^^^^^^ const reference
    return float(s.a+s.b)/2.0;
}

这避免了不必要的参数副本。