std ::查找一组shared_ptr

Question

I'm sure I'm doing something stupid here, but I can't see it. Why doesn't the following compile?

#include <algorithm>
#include <memory>
#include <vector>
#include <string>

// A class to play with.  Encapsulates a name.
class StringClass
{
public:
    StringClass(std::string const & name) : MyName(name) 
    {
    }

    std::string const & Name() const
    {
        return MyName;
    }

private:
    std::string MyName;
};

// The set of instances of "StringClass".

std::vector<std::shared_ptr<StringClass>> MyInstances;

// Function returns "true" if a class with the given name exists in the collection.
bool Exists(std::string const & name)
{
    auto i = std::find(MyInstances.begin(), MyInstances.end(), [&](std::shared_ptr<StringClass> const & instance) {
        return instance->Name() == name;
    });

    return i != MyInstances.end();
}

I've made a vector of shared_ptr to a class. The class has a Name() property. All I want to do is iterate the vector looking for an instance of the class with the given name. However, it doesn't compile :(.

Errors are:

1>ClCompile: 1> test.cpp 1>c:\\program files (x86)\\microsoft visual studio 10.0\\vc\\include\\algorithm(41): error C2679: binary '==' : no operator found which takes a right-hand operand of type 'const anonymous-namespace'::<lambda0>' (or there is no acceptable conversion) 1> could be 'built-in C++ operator==(std::_Bool_type, std::_Bool_type)' 1> c:\\program files (x86)\\microsoft visual studio 10.0\\vc\\include\\exception(470): or 'bool std::operator ==(const std::_Exception_ptr &,const std::_Exception_ptr &)' 1> c:\\program files (x86)\\microsoft visual studio 10.0\\vc\\include\\exception(475): or 'bool std::operator ==(std::_Null_type,const std::_Exception_ptr &)' 1>
c:\\program files (x86)\\microsoft visual studio 10.0\\vc\\include\\exception(481): or 'bool std::operator ==(const std::_Exception_ptr &,std::_Null_type)' 1> c:\\program files (x86)\\microsoft visual studio 10.0\\vc\\include\\system_error(408): or
'bool std::operator ==(const std::error_code &,const std::error_condition &)' 1> c:\\program files (x86)\\microsoft visual studio 10.0\\vc\\include\\system_error(416): or 'bool std::operator ==(const std::error_condition &,const std::error_code &)' 1> while trying to match the argument list '(std::tr1::shared_ptr<_Ty>, const anonymous-namespace'::<lambda0>' (or there is no acceptable conversion) 1> could be 'built-in C++ operator==(std::_Bool_type, std::_Bool_type)' 1> c:\\program files (x86)\\microsoft visual studio 10.0\\vc\\include\\exception(470): or 'bool std::operator ==(const std::_Exception_ptr &,const std::_Exception_ptr &)' 1> c:\\program files (x86)\\microsoft visual studio 10.0\\vc\\include\\exception(475): or 'bool std::operator ==(std::_Null_type,const std::_Exception_ptr &)' 1>
c:\\program files (x86)\\microsoft visual studio 10.0\\vc\\include\\exception(481): or 'bool std::operator ==(const std::_Exception_ptr &,std::_Null_type)' 1> c:\\program files (x86)\\microsoft visual studio 10.0\\vc\\include\\system_error(408): or
'bool std::operator ==(const std::error_code &,const std::error_condition &)' 1> c:\\program files (x86)\\microsoft visual studio 10.0\\vc\\include\\system_error(416): or 'bool std::operator ==(const std::error_condition &,const std::error_code &)' 1> while trying to match the argument list '(std::tr1::shared_ptr<_Ty>, const anonymous-namespace'::<lambda0>' (or there is no acceptable conversion) 1> could be 'built-in C++ operator==(std::_Bool_type, std::_Bool_type)' 1> c:\\program files (x86)\\microsoft visual studio 10.0\\vc\\include\\exception(470): or 'bool std::operator ==(const std::_Exception_ptr &,const std::_Exception_ptr &)' 1> c:\\program files (x86)\\microsoft visual studio 10.0\\vc\\include\\exception(475): or 'bool std::operator ==(std::_Null_type,const std::_Exception_ptr &)' 1>
c:\\program files (x86)\\microsoft visual studio 10.0\\vc\\include\\exception(481): or 'bool std::operator ==(const std::_Exception_ptr &,std::_Null_type)' 1> c:\\program files (x86)\\microsoft visual studio 10.0\\vc\\include\\system_error(408): or
'bool std::operator ==(const std::error_code &,const std::error_condition &)' 1> c:\\program files (x86)\\microsoft visual studio 10.0\\vc\\include\\system_error(416): or 'bool std::operator ==(const std::error_condition &,const std::error_code &)' 1> while trying to match the argument list '(std::tr1::shared_ptr<_Ty>, const anonymous-namespace'::)' 1> with 1> [ 1> _Ty=StringClass 1>
] 1> c:\\program files (x86)\\microsoft visual studio 10.0\\vc\\include\\algorithm(74) : see reference to function template instantiation '_InIt std::_Find*, anonymous-namespace'::<lambda0>>(_InIt,_InIt,const anonymous-namespace':: &)' being compiled 1> with 1> [ 1> _InIt=std::tr1::shared_ptr *, 1> _Ty=StringClass 1> ] 1> c:\\svn\\trunk\\test\\test\\test.cpp(55) : see reference to function template instantiation '_InIt std::find, anonymous-namespace'::<lambda0>>(_InIt,_InIt,const _Ty &)' being compiled 1> with 1> [ 1> _InIt=std::_Vector_iterator<std::_Vector_val<std::tr1::shared_ptr<StringClass>,std::allocator<std::tr1::shared_ptr<StringClass>>>>, 1>
_Myvec=std::_Vector_val<std::tr1::shared_ptr<StringClass>,std::allocator<std::tr1::shared_ptr<StringClass>>>, 1> _Ty= anonymous-namespace'::<lambda0>>(_InIt,_InIt,const _Ty &)' being compiled 1> with 1> [ 1> _InIt=std::_Vector_iterator<std::_Vector_val<std::tr1::shared_ptr<StringClass>,std::allocator<std::tr1::shared_ptr<StringClass>>>>, 1>
_Myvec=std::_Vector_val<std::tr1::shared_ptr<StringClass>,std::allocator<std::tr1::shared_ptr<StringClass>>>, 1> _Ty= anonymous-namespace'::<lambda0>>(_InIt,_InIt,const _Ty &)' being compiled 1> with 1> [ 1> _InIt=std::_Vector_iterator<std::_Vector_val<std::tr1::shared_ptr<StringClass>,std::allocator<std::tr1::shared_ptr<StringClass>>>>, 1>
_Myvec=std::_Vector_val<std::tr1::shared_ptr<StringClass>,std::allocator<std::tr1::shared_ptr<StringClass>>>, 1> _Ty= anonymous-namespace':: 1> ] 1> stdafx.cpp 1> Generating Code... 1> 1>Build FAILED. 1> 1>Time Elapsed 00:00:00.87 ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

Answer 1

You want to use find_if , not find . Find searches for a value, find_if takes a predicate.