一个输出操作符重载的有关问题_QT开发

求助一个输出操作符重载的问题
直接上代码

customer.h

C/C++ code

#ifndef _CUSTOMER_H#define _CUSTOMER_H#include <QString>#include <QTextStream>#include <QObject>class Customer:public QObject{    Q_OBJECTpublic:    explicit Customer(const QString &name);    QString toString() const;        friend QTextStream& operator << (QTextStream &out, const Customer &c);};#endif

customer.cpp

C/C++ code

#include "customer.h"#include "customer.h"Customer::Customer(const QString &name){    setObjectName(name);}QString Customer:: toString() const{    QString retval =  QString("Student ") + objectName();    return retval;}QTextStream& Customer::operator << (QTextStream &out, const Customer &c){    out << c.toString() ;    return out;}

main.cpp

C/C++ code

#include <QApplication>#include <QList>#include <QDebug>#include "customer.h"int main(){    QObject root;    Customer *name1 = new Customer("a");    name1->setParent(&root);    Customer *name2 = new Customer("b");    name2->setParent(&root);    QObject *name3 = new QObject;    name3->setObjectName("c");    name3->setParent(&root);    QList<Customer *> list = root.findChildren<Customer*>();    foreach(const Customer *current ,list)    {        qDebug() << current->toString() << " ";    }    return 0;}

大家看头文件我把输出操作符放类中友元访问报错：错误:C2039: “<<”: 不是“Customer”的成员为什么会报错呢？如果把这个函数去掉friend 放类外实现文件去掉Customer:: 编译就通过我记得在C++环境下输出操作符重载可以作为友元放在类中的。。。。为什么会这样呢？

------解决方案--------------------
QTextStream& Customer::operator << (QTextStream &out, const Customer &c)
{
out << c.toString() ;
return out;
}

啊~你的实现表示的是在Customer这类里的嘛。。。