C++面试相关题目集合选摘

关于继承、多态、重写、重载等：

#ifndef _PRINTHELLO_H_
#define _PRINTHELLO_H_

#include<stdio.h>

class PrintHello {
public:
static PrintHello* instance();
static void uninstance();
~PrintHello();
private:
PrintHello();
private:
static PrintHello* _instance;
};
//唯一标识符
PrintHello* PrintHello::_instance = NULL;
#define PrintHelloInstance PrintHello::instance()

PrintHello::PrintHello() {
printf("Hello World!\n");
}

PrintHello* PrintHello::instance() {
if(_instance==NULL){
_instance = new PrintHello();
}
return _instance;
}

void PrintHello::uninstance() {
if (_instance){
delete _instance;
_instance = NULL;
}
}

PrintHello::~PrintHello() {
printf("~Hello World!\n");
}

#endif

#ifndef _SHAPE_H_
#define _SHAPE_H_

class Triangle;
class Rectangle;
class Shape
{
public:
bool isShape() {
return true;
}
virtual int getSides(){//声明为虚函数，子类重写才起作用
printf("---in Shape::getSides()---\n");
return 0;
}
int getSides(Triangle* tri){
printf("---in Shape::getSides(Triangle* tri)---\n");
return 3;
}
int getSides(Rectangle* rec){
return 4;
}
virtual void vvv() = 0;//纯虚函数不能实例化
protected:
private:
};

class Triangle : public Shape
{
public:
int getSides(){//重写，实现多态
printf("---in Triangle::getSides()---\n");
return 3;
}
int getSides(int i){//重载，子类特有
return i;
}
void vvv(){//子类必须实现基类的接口
printf("in Triangle::vvv\n");
}
protected:
private:
};

class Rectangle : public Shape
{
public:
int getSides(int i){//重载，子类特有
return i;
}
protected:
private:
};

#endif

#include "hello.hpp"
#include <iostream>
#include "Shape.h"

int fn1(void){
printf("fn1...\n");
return 0;
}

int a = fn1(); //全局变量,运行于main之前
//在main函数之前调用

/*class*/ struct A
{
int aa;
public:
A(){ int abc = 10; };
virtual ~A(){};
public:
void hello(){ printf("Hello World!\n"); }
};

/*class*/ struct B : A
{
int aa;
int bb;
static int cc;
public:
B(){};
virtual ~B(){};
};

/*class*/ struct C : B
{
char cc;
public:
C(){};
~C(){};
};

int main(int argc, char* argv[]){
printf("I am in main----1111\n");
PrintHello::instance()->uninstance();
printf("I am in main----2222\n");

char *p[] = { "TENCENT", "CAMPUS", "RECRUITING" };
char **pp[] = {p+2, p+1, p};//{ "RECRUITING", "CAMPUS", "TENCENT" }
char ***ppp = pp;// "RECRUITING"
printf("%s", **++ppp);// "CAMPUS"
printf("%s", *++*++ppp);// p + 1

float a[10], x;
float b = *&a[1];//优先级从右到左

const char *pStr = "sss";//字符串常量
pStr = "abb";

char a1[] = { 'a', 'b', 'c' };
char a2[] = { "abc" };//{'a', 'b', 'c', '\0'}

int i = 10, j = 2;
i *= j + 8;//优先级 + > *=

char acX[] = "abc";//{ 'a', 'b', 'c', '\0' }
char acY[] = { 'a', 'b', 'c' };
char *szX = "abc";
char *szY = "abc";//szX和szY指向同一内存地址
acX[0] = 'h';
acY[0] = 'h';

A sa;//sizeof(sa)==8
B sb;//sizeof(sb)==16
C sc;//sizeof(sc)==20//字节对齐
printf("\nsizeof(A)=%d, sizeof(B)=%d, sizeof(C)=%d\n", sizeof(sa), sizeof(sb), sizeof(sc));

//多态测试
Shape* pShape = new Triangle();
printf("Shape=%d\n", pShape->getSides());
printf("Shape=%d\n", pShape->getSides((Triangle*)pShape));
//顺序从后面往前！！！
printf("Shape=%d, %d\n", pShape->getSides(), pShape->getSides((Triangle*)pShape));

if ('q'==getchar()) {
exit(0);
}
return 0;
}