vs2013 C++ error link2001

class Graph
{
protected:
    size_t numVertex = 0, numEdge = 0;

public:
    virtual size_t n() = 0;                               //返回顶点数
    virtual size_t e() = 0;                               //返回目前的边数
    virtual int first(size_t ) = 0;                       //返回第一个neighbour
    virtual int next(size_t, size_t ) = 0;                   //返回第2个neighbour
    virtual void setEdge(size_t v1, size_t v2, int weight);              //  =0  =0  =0  =0  =0  =0  =0  =0  =0  =0
    virtual void delEdge(size_t v1, size_t v2);                               //  =0  =0  =0  =0  =0  =0  =0  =0  =0  =0
    virtual int weight(size_t v1, size_t v2) = 0;                   //返回两点之间距离
    virtual bool getMark(size_t v) = 0;                   //返回指定顶点的标记值

};