c++ - 在结构 vector 中搜索

Question

我有一个充满结构的 vector ，如下所示

struct person_t
{

    string name;
    string id;
    struct location_t location;    
};

    vector <person_t> myvector;

我已经阅读了 myvector 中的项目

但现在我需要知道如何在 vector 中搜索特定项目并计算该项目在 vector 中的数量。

Answer 1

unsigned int count = std::count_if( myvector.begin(), myvector.begin(),
    []( const person_t & p ) { return p.name == "Bill Gates"; }
);

或者没有c++11

struct EqualByName {
    EqualByName( const std::string & name ) : m_name( name ) {}
    bool operator()( const person_t & p ) const { return p.name == m_name; }
private:
    std::string m_name;
};
unsigned int count = std::count_if( myvector.begin(), myvector.begin(),
    EqualByName( "Bill Gates" )
);

或者看起来很丑但适用于所有场合 ))

template< class T, class FieldType, FieldType T::*FieldPtr >
struct EqualBy
{
    EqualBy( const FieldType & value ) : m_fieldValue( value ) {}
    bool operator()( const T & r ) const {
        return m_fieldValue == r.*FieldPtr;
    }
    bool operator()( const T * p ) const {
        return m_fieldValue == p->*FieldPtr;
    }
private:
    const FieldType m_fieldValue;
};

// usage:
typedef EqualBy< person_t, std::string, & person_t::name > EqualByName;
typedef EqualBy< person_t, std::string, & person_t::id > EqualById;
unsigned int namesCount = std::count_if( myvector.begin(), myvector.end(),
    EqualByName( "Bill Gates" )
);
unsigned int idsCount = std::count_if( myvector.begin(), myvector.end(),
    EqualById( "123456" )
);