1.引用的好处
代码语言：javascript复制#include
using namespace std;
void swapr( int a, int b);
void swapp(int &a, int &b);
void swapv( int* a, int* b);
int main()
{
int wallet1 = 100, wallet2 = 50;
cout << "wallet1=" << wallet1;
cout << "wallet2=" << wallet2 << endl;
swapr(wallet1, wallet2);
cout << "wallet1=" << wallet1;
cout << "wallet2=" << wallet2 << endl;
swapp(wallet1, wallet2);
cout << "wallet1=" << wallet1;
cout << "wallet2=" << wallet2 << endl;
swapv(&wallet1, &wallet2);
cout << "wallet1=" << wallet1;
cout << "wallet2=" << wallet2 << endl;
return 0;
}
void swapr(int a, int b)
{
int temp = a;
a = b;
b = temp;
}
void swapp(int &a, int &b)
{
int temp = a;
a = b;
b = temp;
}
void swapv( int* a, int* b)
{
int temp = *a;
*a = *b;
*b = temp;
}其中运用了指针，引用进行数互换，但是它们所执行完的效果却是不一样的。 通过观察发现，引用传递和按值传递的形式类似，只能从它对于函数的定义里才能看出区别。 引用和指针成功交换了wallet里的内容，值传递却没能完成这个任务。在引用传递中，a,b是wallet1,wallet2的别名，值传递，a,b是复制了wallet1和wallet2里面的内容，因此交换a,b就不会影响实参的值。
2.尽可能使用const,引用非常适用于结构和类
代码语言：javascript复制#include
#include
struct free_throws
{
std::string name;
int made;
int attempts;
float percent;
};
void display(const free_throws& ft);
void set_pc(free_throws& ft);
free_throws& accumulate(free_throws& target, const free_throws& source);
int main()
{
// partial initializations – remaining members set to 0
free_throws one = { "Ifelsa Branch", 13, 14 };
free_throws two = { "Andor Knott", 10, 16 };
free_throws three = { "Minnie Max", 7, 9 };
free_throws four = { "Whily Looper", 5, 9 };
free_throws five = { "Long Long", 6, 14 };
free_throws team = { "Throwgoods", 0, 0 };
// no initialization
free_throws dup;
set_pc(one);
display(one);
accumulate(team, one);
display(team);
// use return value as argument
display(accumulate(team, two));
accumulate(accumulate(team, three), four);
display(team);
// use return value in assignment
dup = accumulate(team, five);
std::cout << "Displaying team:n";
display(team);
std::cout << "Displaying dup after assignment:n";
display(dup);
set_pc(four);
// ill-advised assignment
accumulate(dup, five) = four;
std::cout << "Displaying dup after ill-advised assignment:n";
display(dup);
return 0;
}
void display(const free_throws& ft)
{
using std::cout;
cout << "Name: " << ft.name << 'n';
cout << " Made: " << ft.made << 't';
cout << "Attempts: " << ft.attempts << 't';
cout << "Percent: " << ft.percent << 'n';
}
void set_pc(free_throws& ft)
{
if (ft.attempts != 0)
ft.percent = 100.0f * float(ft.made) / float(ft.attempts);
else
ft.percent = 0;
}
free_throws& accumulate(free_throws& target, const free_throws& source)
{
target.attempts = source.attempts;
target.made = source.made;
set_pc(target);
return target;
}此代码运用了大量的引用 我们会发现最后的accumulate()函数比较奇特，它是返回了结构的引用，如果它是返回一个结构，将把结构复制到一个临时位置，再将这个拷贝复制给dup,但在返回值引用的时候，直接把team复制到dup,它的效率更高。
3.程序崩溃
代码语言：javascript复制#include
#include
using namespace std;
string version1(const string& s1, const string& s2);
const string& version2(string& s1, const string& s2); // has side effect
const string& version3(string& s1, const string& s2); // bad design
int main()
{
string input;
string copy;
string result;
cout << "Enter a string: ";
getline(cin, input);
copy = input;
cout << "Your string as entered: " << input << endl;
result = version1(input, "***");
cout << "Your string enhanced: " << result << endl;
cout << "Your original string: " << input << endl;
result = version2(input, "###");
cout << "Your string enhanced: " << result << endl;
cout << "Your original string: " << input << endl;
cout << "Resetting original string.n";
input = copy;
result = version3(input, "@@@");
cout << "Your string enhanced: " << result << endl;//存在错误
cout << "Your original string: " << input << endl;
return 0;
}
string version1(const string& s1, const string& s2)
{
string temp;
temp = s2 s1 s2;
return temp;
}
const string& version2(string& s1, const string& s2) // has side effect
{
s1 = s2 s1 s2;
// safe to return reference passed to function
return s1;
}
const string& version3(string& s1, const string& s2) // bad design
{
string temp;
temp = s2 s1 s2;
// unsafe to return reference to local variable
return temp;
}temp是一个新的string对象，执行完函数，它将不复存在，因此返回指向temp的引用不可行。这也是第三个函数崩溃的原因。
