C++基础知识面试精选100题系列(21-30)[C++ basics]

【本文链接】

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【题目21】

运行下面的代码，输出结果？

【代码】

C++ Code

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/* version: 1.0 author: hellogiser blog: http://www.cnblogs.com/hellogiser date: 2014/9/22 */ #include "stdafx.h" #include <iostream> using namespace std; class A { public: virtual void Fun(int number = 10) { std::cout << "A::Fun with number " << number << endl; } }; class B: public A { public: virtual void Fun(int number = 20) { std::cout << "B::Fun with number " << number << endl; } }; int main() { B b; A &a = b; a.Fun(); return 0; //虚函数动态绑定：B，缺省实参是编译时确定的。。。为10 } /* B::Fun with number 10 */

【分析】

虚函数动态绑定，但是缺省实参是编译时确定的，所以结果为B::Fun with number 10

【题目22】

指出下面的程序有哪些错误，并改正。

【代码】

C++ Code

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#include <iostream> using namespace std; class A { public: A(); ~A(); int i = 0; // ERROR static int j = 0; // ERROR const int k = 0; // ERROR const static char *p = "Hello world"; // ERROR static void fun(); }; A::A() { } A::~A() { } static void fun() // ERROR { }

【正确代码】

C++ Code

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/* version: 1.0 author: hellogiser blog: http://www.cnblogs.com/hellogiser date: 2014/9/22 */ #include "stdafx.h" #include <iostream> using namespace std; class A { public: A(); ~A(); int i ; // error static int j ; // error const int k ; // error const static char *p; // error static void fun(); }; int A::j = 0; const char *A::p = "hello world"; A::A(): i(0), k(0) { } A::~A() { } void A::fun() { } int main() { return 0; }

【题目23】

代码结果？

C++ Code

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/* version: 1.0 author: hellogiser blog: http://www.cnblogs.com/hellogiser date: 2014/9/24 */ #include "stdafx.h" #include <iostream> using namespace std; class Base { public: int Bar(char x) { return (int)(x); } virtual int Bar(int x) { return(2 * x); } }; class Derived : public Base { public: int Bar(char x) { return(int)(-x); } int Bar(int x) { return (x / 2); } }; int main() { Derived Obj; Base *pObj = &Obj; printf("%d,", pObj->Bar((char)(100))); // base::Bar printf("%d,", pObj->Bar(100)); // derived::Bar return 0; } /* 100 50 */

分析：虚函数和普通函数

基类指针指向派生类对象，虚函数调用派生类的，普通函数调用基类的。

【题目24】

下面代码运行结果？

C++ Code

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/* version: 1.0 author: hellogiser blog: http://www.cnblogs.com/hellogiser date: 2014/9/25 */ #include "stdafx.h" #include <iostream> using namespace std; void test_longlong_little_endian() { // little-endian long long a = 1, b = 2, c = 3; printf("%d %d %d %d %d %d\n", a, b, c); // 1 0 2 0 3 0 printf("%d %d %d\n", a, b, c); // 1 0 2 } int main() { test_longlong_little_endian(); return 0; }

C++ Code

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void test() { char *p1 = "hello"; char *p2 = "world"; printf("%s %s %s\n", p1, p2); // hello world ??? }

【题目25】