在结构矢量中搜索

Question

我有一个带有结构的向量看起来像这样

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向量中搜索特定项目并计算它在向量中的项目数量.

Answer 1

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

或没有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" )
);

或看起来丑陋,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" )
);