语法错误:需要声明。为什么gsoap不能读取矢量?

我正在用gsoap编写一个web服务。当我编译此代码时,它会给我错误:
语法错误:需要声明
当我移除向量时,它编译成功,

#include <stdsoap2.h>
#include <vector>

//gsoap ns service name:    PersonData
//gsoap ns service style:   document
//gsoap ns service encoding:    literal
//gsoap ns service namespace:   http://localhost/PersonData.wsdl
//gsoap ns service location:    http://localhost:7777
//gsoap ns schema namespace: urn:PersonData



class PersonInfo 
{
 public:
    std::string ID;
    std::string FirstName;
    std::string LastName;
    std::string Sex;
    std::string BirthDate;
    std::string BirthPlace;
    std::string SocialNumber;
};

class MultiplePersons
{
public:
       // It gives error only with vector 
    std::vector<PersonInfo> info; // **here is the error**
};
int ns__getSingleValue(std::string Param, std::string *result);

int ns__getFullRecord(std::string Param, MultiplePersons *result);