Question

师，

给定两个类定义如下（省略属性，方法和实现）：

struct A { friend std::ostream& operator << (std::ostream& o, const A& c); };
struct B { friend std::ostream& operator << (std::ostream& o, const B& c); };

我使用了以下课程：

ln 1: A *arrayA = new A[10];
ln 2: B *arrayB = new B[10];
ln 3: /* some codes to initialize arrayA and arrayB */
ln 4: for (int i = 0; i < 10; i++) { std::cout << arrayA[i]; } // this work 
ln 5: for (int j = 0; j < 10; j++) { std::cout << arrayB[j]; } // this complain

我的编译器抱怨B类为

error: cannot bind 'std::ostream {aka std::basic_ostream<char>}' lvalue 
to 'std::basic_ostream<char>&&'

../lib/gcc/mingw32/4.6.1/include/c++/ostream:581:5 error initializing argument 1 
of 'std::basic_ostream<_CharT, _Traits>& 
std::operator<<(std::basic_ostream<_CharT, _Traits>&&, const _Tp&) 
 [with _CharT = char, _Traits = std::char_traits<char>, _Tp = ClsB]

我不知道第5行有什么问题。评论主程序的第5行给出了我的良好编译，这意味着我对运算符的定义＆lt;＆lt;因为B类在语法上是正确的。请给出任何指示并表示感谢。

Yam Hon

平台：win 7
MinGW32：版本2011-11-08
GNU Make 3.82
G ++版本4.6.1

[编辑1] 我的程序实际上有两个以上的类，我的所有类都有运算符＆lt;＆lt;重载以进行调试。我为所有类使用了相同的签名（带有适当的第二个参数）。只有B级才会出现此错误。

[编辑2] 完整版的课程：

struct CPeople { // this is class B
int age;
int ageGroup;

int zipcode;
int communityID;
int areaID;
int familyID;
int contactID;
int contactType; /* P, D, E, M, H, W */
int state;
int vaccinated; /* 0 = unvac, 1 = vaccinated */

friend std::ostream& operator<< (std::ostream& o, const CPeople& c)
{
    o << "CPeople (" << static_cast<void const *>(&c) << "): "
      << "\tAge Group: "   << c.ageGroup
      << "\tZip Code: "    << c.zipcode
      << "\tCommunityID: " << c.communityID
      << "\tArea ID: "     << c.areaID
      << "\tFamily ID: "   << c.familyID
      << "\tSchool Type: " << c.contactType
      << "\tContact ID: "  << c.contactID
      << "\tState: "       << c.state
      << "\tVaccination: " << c.vaccinated;
    return (o << std::endl);
}
};

struct CWorkGroup : public CContact { // this is class A
/* to which community this member belongs */
std::vector<long> member_com;
CStatistics statistics;

friend std::ostream& operator<< (std::ostream& o, const CWorkGroup& c)
{
    o << "CWorkGroup (" << static_cast<void const *>(&c) << "): ";
    o << "avflag = " << c.avflag << "; member: " << c.size();
    for (int i = 0; i < c.size(); i++)
    {
        o << "; (" << i << " = " << c.member[i] << ")";
    }
    o << std::endl;
    return (o << c.statistics);
}
};

用法A：

for (int i = 0; i < cntWG; i++) { std::clog << WG[i]; } std::clog << std::endl;

用法B（这是错误）：

CPeople *people_total = new CPeople[cntTotalPop];
for (pIdx = 0; pIdx < cntTotalPop; pIdx++)
{
    std::cout << people_total[pIdx];
}

Answer 1

类和结构需要以分号结束，因此在两行的末尾添加分号：

struct A { friend std::ostream& operator << (std::ostream& o, const A& c); };
struct B { friend std::ostream& operator << (std::ostream& o, const B& c); };

无法绑定运算符＆lt;＆lt;在cpp

1 个答案: