how find an object in std::vector
I have an object like below
class MyClass{
int a;
double b;
};
and
vector<MyClass> vMyClass;
then I want search in vMyClass try to use algorithm function:
if( std::find(vMyClass.begin(), vMyClass.end(), aiField) == vMyClass.end())
I also defined operator==
int operator ==(Field &Left,Field &Right)
{
return memcmp(&Left,&Right,sizeof(Field));
}
or
int operator ==(Field &Right)
{
return memcmp(this,&Right,sizeof(Field));
}
but I get an error message.
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开发者_开发技巧>(_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...
They need to be const references. And memcmp
is really, really bad- just perform a member-wise comparison.
You forgot the const
qualifier in your ==
operator, plus it should return bool
, not int
. Just use this instead:
bool operator ==(const Field &Left, const Field &Right)
{
return (Left.a == Right.a) && (Left.b == Right.b);
}
You have a vector of MyClass
, but an comparision operator for Field
. You have to write an
bool operator == (const MyClass &, const MyClass &)
.
This operator should (as others indicated), not use memcmp
, but rather perform a member-wise comparison.
Implement the operator within the class itself:
class MyClass
{
public:
int a;
double b;
bool operator ==(const MyClass &Right) const
{
return (a == Right.a) && (b == Right.b); // 'this' is left
}
};
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