c++ - 如何在 std::vector 中找到一个对象

Question

我有一个像下面这样的对象

 class MyClass{
   int a;
   double b;
 };

和

 vector<MyClass> vMyClass;

然后我想在 vMyClass 中搜索尝试使用算法函数:

 if( std::find(vMyClass.begin(), vMyClass.end(), aiField) == vMyClass.end())

我还定义了operator==

 int operator ==(Field &Left,Field &Right)
 {
    return memcmp(&Left,&Right,sizeof(Field));
 }

或

int operator ==(Field &Right)
{
    return memcmp(this,&Right,sizeof(Field));
}

但我收到一条错误消息。

1>c:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\include\algorithm(40) : error C2678: binary '==' : no operator found which takes a left-hand operand of type 'MyClass' (or there is no acceptable conversion)
1>        C:\Program Files\Microsoft SDKs\Windows\v6.0A\include\guiddef.h(192): could be 'int operator ==(const GUID &,const GUID &)' [found using argument-dependent lookup]
1>        c:\users\shmuelian\documents\visual studio 2008\projects\src\examples\DLgenerator\DLParser.h(85): or       'int operator ==(MyClass &,MyClass &)' [found using argument-dependent lookup]
1>        c:\users\shmuelian\documents\visual studio 2008\projects\src\examples\DLgenerator\DLParser.h(70): or       'int MyClass::operator ==(MyClass &)'
1>        while trying to match the argument list '(MyClass, const MyClass)'
1>        c:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\include\algorithm(74) : see reference to function template instantiation '_InIt std::_Find<std::_Vector_iterator<_Ty,_Alloc>,_Ty>(_InIt,_InIt,const _Ty &)' being compiled
1>        with
1>        [
1>            _InIt=std::_Vector_iterator<MyClass,std::allocator<MyClass>>,
1>            _Ty=MyClass,
1>            _Alloc=std::allocator<MyClass>
1>        ]
1>        c:\users\shmuelian\documents\visual studio 2008\projects\src\examples\DLgenerator\DLParser.h(108) : see reference to function template instantiation '_InIt std::find<std::_Vector_iterator<_Ty,_Alloc>,MyClass>(_InIt,_InIt,const _Ty &)' being compiled
1>        with
1>        [
1>            _InIt=std::_Vector_iterator<MyClass,std::allocator<MyClass>>,
1>            _Ty=MyClass,
1>            _Alloc=std::allocator<MyClass>
1>        ]
1>CommandArgParser.cpp
1>Generating Code...

Answer 1

它们需要是常量引用。 memcmp 真的非常糟糕 - 只需执行成员比较即可。