c_cpp c ++基本模板

Posted 2021-05-14

// Enumerations
enum Day { SUN, MON, TUE, WED, THU, FRI, SAT };
enum Mood { HAPPY = 3, SAD = 1, ANXIOUS = 4, SLEEPY = 2 };
Day today = THU; // today may be any of MON . . . SAT
Mood myMood = SLEEPY; // myMood may be HAPPY, . . ., SLEEPY

// pointers
char ch = ’Q’;
char* p = &ch; // p holds the address of ch
cout << *p; // outputs the character ’Q’
ch = ’Z’; // ch now holds ’Z’
cout << *p; // outputs the character ’Z’
*p = ’X’; // ch now holds ’X’
cout << ch; // outputs the character ’X’
// note
int* x, y, z; // same as: int* x; int y; int z;

// Arrays
double f[5]; // array of 5 doubles: f[0], . . ., f[4]
int m[10]; // array of 10 ints: m[0], . . ., m[9]
f[4] = 2.5;
m[2] = 4;
cout << f[m[2]]; // outputs f[4], which is 2.5
int a[ ] = {10, 11, 12, 13}; // declares and initializes a[4]
bool b[ ] = {false, true}; // declares and initializes b[2]
char c[ ] = {’c’, ’a’, ’t’}; // declares and initializes c[3]

// Arrays and pointers
char c[ ] = {’c’, ’a’, ’t’};
char* p = c; // p points to c[0]
char* q = &c[0]; // q also points to c[0]
cout << c[2] << p[2] << q[2]; // outputs “ttt”

// C-style structure
enum MealType { NO_PREF, REGULAR, LOW_FAT, VEGETARIAN };
struct Passenger {
    string name; // passenger name
    MealType mealPref; // meal preference
    bool isFreqFlyer; // in the frequent flyer program?
    string freqFlyerNo; // the passenger’s freq. flyer number
};
Passenger pass = { "John Smith", VEGETARIAN, true, "293145" };
// change
pass.name = "Pocahontas"; // change name
pass.mealPref = REGULAR; // change meal preference

// Reference
string author = "Samuel Clemens";
string& penName = author; // penName is an **alias** for author
penName = "Mark Twain"; // now author = “Mark Twain”
cout << author; // outputs “Mark Twain”

// Traditional C-Style Casting
int i1 = 18;
int i2 = 16;
double dv1 = i1 / i2; // dv1 has value 1.0
double dv2 = double(i1) / double(i2); // dv2 has value 1.125
double dv3 = double( i1 / i2 ); // dv3 has value 1.0

// Static Casting
double d1 = 3.2;
double d2 = 3.9999;
int i1 = static_cast<int>(d1); // i1 has value 3
int i2 = static_cast<int>(d2); // i2 has value 3

// Function overriding
void print(int x)
{
    cout << x << endl;
}
void print(const Passenger& passenger)
{
    cout << passenger.name << " " << passenger.mealPref;
    if (passenger.isFreqFlyer)
    {
        cout << " " << passenger.freqFlyerNo;
    }
    cout << endl;
}

// operator overriding
bool operator==(const Passenger& x, const Passenger& y)
{
    return x.name == y.name &&
        x.mealPref == y.mealPref &&
        x.isFreqFlyer == y.isFreqFlyer &&
        x.freqFlyerNo == y.freqFlyerNo;
}
ostream& operator<<(ostream& out, const Passenger& passenger)
{
    out << passenger.name << " " << passenger.mealPref;
    if (passenger.isFreqFlyer) {
        cout << " " << passenger.freqFlyerNo;
    }
    out << endl;

    return out;
}

// inline function
inline int min(int x, int y) { return (x < y ? x : y); }

// class
class Passenger {
private:
// . . .
public:
  Passenger(); // default constructor
  Passenger(const string& nm, MealType mp, const string& ffn = "NONE");
  Passenger(const Passenger& pass); // copy constructor
// . . .
};
Passenger::Passenger() { // default constructor
name = "--NO NAME--";
mealPref = NO PREF;
isFreqFlyer = false;
freqFlyerNo = "NONE";
}
// constructor given member values
Passenger::Passenger(const string& nm, MealType mp, const string& ffn) {
  name = nm;
  mealPref = mp;
  isFreqFlyer = (ffn != "NONE"); // true only if ffn given
  freqFlyerNo = ffn;
}
// copy constructor
Passenger::Passenger(const Passenger& pass) {
  name = pass.name;
  mealPref = pass.mealPref;
  isFreqFlyer = pass.isFreqFlyer;
  freqFlyerNo = pass.freqFlyerNo;
}
// constructor using an initializer list
Passenger::Passenger(const string& nm, MealType mp, string ffn)
: name(nm), mealPref(mp), isFreqFlyer(ffn != "NONE")
{ freqFlyerNo = ffn; }

// class note
Every class that allocates its own objects using new should:
• Define a destructor to free any allocated objects.
• Define a copy constructor, which allocates its own new member storage
and copies the contents of member variables.
• Define an assignment operator, which deallocates old storage, allocates
new storage, and copies all member variables.