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>
anonymous-namespace'::)' 1> with 1> [ 1> _Ty=StringClass 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
] 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>
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 ==========
_Myvec=std::_Vector_val<std::tr1::shared_ptr<StringClass>,std::allocator<std::tr1::shared_ptr<StringClass>>>, 1> _Ty=
You want to use find_if
, not find
. Find
searches for a value, find_if
takes a predicate.
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