c++ - 为什么这个 std::find 不能比较这些对象

Question

通常当我执行 std::find 时，我会将谓词作为第三个参数，但这次我想我会做不同的，我不明白为什么它不起作用。

#include <iostream>
#include <vector>
#include <algorithm>

struct RenderJob
{
    RenderJob() {};
    int renderJob_ID;
    bool operator==(RenderJob& rhs) { return rhs.renderJob_ID == this->renderJob_ID; }
};

int main()
{
    RenderJob foo;
    RenderJob foo2;
    foo == foo2; // Works

    std::vector<RenderJob> renderJobs;

    std::find(renderJobs.begin(), renderJobs.end(), foo); // Doesn't work
}

binary "==" no operator found which takes a left-handed operand of type RenderJob (or there is no acceptable conversion)

编辑:谢谢您的回答。以下是它失败原因的一些示例

    RenderJob foo;
    RenderJob foo2;
    foo == foo2; // Works

    std::vector<RenderJob> renderJobs;

    std::vector<RenderJob>::const_iterator constit = renderJobs.begin();

    *constit == foo2;  // Doesn't work

更简单的例子:

 const RenderJob* pToRenderJob;

*pToRenderJob == foo2;  // This fails because the pointed to 
                        // object is const, and cannot call the 
                        // operator== function because the actual function
                        // definition is not const. 

如果反过来:

foo2 == *pToRenderJob; // This would fail because the 
                        // operator==(RenderJob&) the actual argument 
                        // is not const. Very subtle rules

Answer 1

你离开了你的 const 限定符。

bool operator==(const RenderJob& rhs) const { ... }