Think_in_CPP第十二章 操作符重载(4)

12.5 其他操作符

12.5.1 操作符[ ]

class IntArray {
enum { sz = 5 };
int i[sz];
public:
IntArray() { memset(i, 0, sz* sizeof(*i)); }
int& operator[](int x) {
require(x >= 0 && x < sz,
"IntArray::operator[] out of range");
return i[x];
}
friend ostream&
operator<<(ostream& os, const IntArray& ia);
friend istream&
operator>>(istream& is, IntArray& ia);
};

ostream&
operator<<(ostream& os, const IntArray& ia) {
for(int j = 0; j < ia.sz; j++) {
os << ia.i[j];
if(j != ia.sz -1)
os << ", ";
}
os << endl;
return os;
}

istream&
operator>>(istream& is, IntArray& ia){
for(int j = 0; j < ia.sz; j++)
is >> ia.i[j];
return is;
}

测试

int main() {
stringstream input("47 34 56 92 103");
IntArray I;
input >> I;
I[4] = -1; // Use overloaded operator[]
cout << I;
}

12.5.2 new和delete

参考13章

12.5.3 逗号重载

#include <iostream>
using namespace std;
class After {
public:
const After& operator,(const After&) const {
cout << "After::operator,()" << endl;
return *this;
}
};

class Before {};
Before& operator,(int, Before& b) {
cout << "Before::operator,()" << endl;
return b;
}

测试

int main() {
After a, b;
a, b; // Operator comma called
Before c;
1, c; // Operator comma called
}

12.5.4 操作符->

#include <iostream>
#include <vector>
#include "../require.h"
using namespace std;
class Obj {
static int i, j;
public:
void f() const { cout << i++ << endl; }
void g() const { cout << j++ << endl; }
};
// Static member definitions:
int Obj::i = 47;
int Obj::j = 11;
// Container:
class ObjContainer {
vector<Obj*> a;
public:
void add(Obj* obj) { a.push_back(obj); }
friend class SmartPointer;
};
class SmartPointer {
ObjContainer& oc;
int index;
public:
SmartPointer(ObjContainer& objc) : oc(objc) {
index = 0;
}
// Return value indicates end of list:
bool operator++() { // Prefix
if(index >= oc.a.size()) return false;
if(oc.a[++index] == 0) return false;
return true;
}
bool operator++(int) { // Postfix
return operator++(); // Use prefix version
}
Obj* operator->() const {
require(oc.a[index] != 0, "Zero value "
"returned by SmartPointer::operator->()");
return oc.a[index];
}
};

测试

int main() {
const int sz = 10;
Obj o[sz];
ObjContainer oc;
for(int i = 0; i < sz; i++)
oc.add(&o[i]); // Fill it up
SmartPointer sp(oc); // Create an iterator
do {
sp->f(); // Pointer dereference operator call
sp->g();
} while(sp++);
}

说明：

1.SmartPointer重载了->，其行为是返回一个Obj指针。sp->f()执行的结果是调用某个Obj对象的f()成员函数。

2.->重载函数应该返回一个指针。

a nested iterator

#include <iostream>
#include <vector>
#include "../require.h"
using namespace std;
class Obj {
static int i, j;
public:
void f() { cout << i++ << endl; }
void g() { cout << j++ << endl; }
};
// Static member definitions:
int Obj::i = 47;
int Obj::j = 11;

// Container:
class ObjContainer {
vector<Obj*> a;
public:
void add(Obj* obj) { a.push_back(obj); }
class SmartPointer;
friend SmartPointer;

class SmartPointer {
ObjContainer& oc;
unsigned int index;
public:
SmartPointer(ObjContainer& objc) : oc(objc) {
index = 0;
}
// Return value indicates end of list:
bool operator++() { // Prefix
if(index >= oc.a.size()) return false;
if(oc.a[++index] == 0) return false;
return true;
}
bool operator++(int) { // Postfix
return operator++(); // Use prefix version
}
Obj* operator->() const {
require(oc.a[index] != 0, "Zero value returned by SmartPointer::operator->()");
return oc.a[index];
}
};
// Function to produce a smart pointer that
// points to the beginning of the ObjContainer:
SmartPointer begin() {
return SmartPointer(*this);
}
};

int main() {
const int sz = 10;
Obj o[sz];
ObjContainer oc;
for(int i = 0; i < sz; i++)
oc.add(&o[i]); // Fill it up
ObjContainer::SmartPointer sp = oc.begin();
do {
sp->f(); // Pointer dereference operator call
sp->g();
} while(++sp);
}