C++小题（一）

/*#include<iostream>using namespace std;static int a=1;void fun1(){a=2;}void fun2(){int a=3;}void fun3(){static int a=4;}int main(){cout<<a;fun1();cout<<a;fun2();cout<<a;fun3();cout<<a;}//1 2 2 2*//*#include<iostream>using namespace std;int main(){int i;for(i=0;i<3;i++){switch(i){case 0:cout<<i;case 2:cout<<i;default:cout<<i;}}}*///0 0 0 1 2 2/* #include<iostream>using namespace std;int function(const int src[16]){int val1=0;int dst[16]={0};int val2=0;const int* psrc=src;fprintf(stdout,"size of src=%lu\n",sizeof(src));for(int i=0;i<=16;i++){dst[i]=*psrc+i;psrc++;}cout<<val1<<" "<<val2;return 0;}int main(){int s[16]={0};function(s);}//4//0 随机一个数*//*#include<iostream>using namespace std;struct A{unsigned int a;char b[2];double c;short d;};int main(){cout<<sizeof(A);}//24*//*#include<iostream>#include<cstring>using namespace std;int main(){char a[]="ABCDEFG";char b[]={'A','B','C','D','E','F','G'};cout<<sizeof(a)<<" "<<sizeof(b)<<" "<<strlen(a)<<" "<<strlen(b);} //8 7 7 7  */  /*#include<iostream>#include<cstring>using namespace std;struct A{uint16_t id;uint32_t value;uint64_t timestamp;};void fool(){A A1={};uint64_t a=0x00010001;memcpy(&A1,&a,sizeof(uint64_t));cout<<A1.id<<" "<<A1.value<<" "<<A1.timestamp;}int main(){fool();}//1 0 0 *//*#include<iostream>#include<cstring>using namespace std;int main(){char dog[]={'\0'};char dog2[]={"wang\0wang"};cout<<sizeof(dog)<<" "<<strlen(dog)<<endl;cout<<sizeof(dog2)<<" "<<strlen(dog2)<<endl; }//1 0 //10 4 *//*#include<stdio.h>class A{public:    void foo()    {        printf("1");    }    virtual void fun()    {        printf("2");    }};class B: public A{public:    void foo()    {        printf("3");    }    void fun()    {        printf("4");    }};int main(void){    A a;    B b;    A *p = &a;    p->foo();    p->fun();    p = &b;    p->foo();    p->fun();    A *ptr = (A *)&b;    ptr->foo();        ptr->fun();    return 0;}//121414  */  /* #include<iostream> using namespace std; class A  {       int i; //4       union U //16      {           char buff[13];           int i;       }u;       void foo() {    }       typedef char* (*f)(void*);       enum {red, green, blue} color ;//4  }a;  int main(){ cout<<sizeof(a);//24 } */  /*  #include<iostream> using namespace std; class A  {  public:      A()  {     }      ~A() {    cout<<"~A"<<endl;   }  };     class B:public A  {      public:          B(A &a):_a(a)          {                       }          ~B()          {              cout<<"~B"<<endl;          }      private:          A _a;      };         int main(void)   {          A a;       //很简单，定义a的时候调用了一次构造函数          B b(a); }// 析构B A A A *//*#include<stdio.h>int main(){   int i=-2147483648;   return printf("%d,%d,%d,%d",~i,-i,1-i,-1-i);}//2147483647*//*#include<iostream>using namespace std;class foo {public:foo(){cout<<"foo()"<<endl;};};class boo : public foo {public:boo() : foo() {cout<<"boo()"<<endl;};};int main(){foo f;boo b;}*//*#include<iostream>using namespace std;class cls{public:cls(int &n,int *m):n(n),m(m){}cls():cls(a,&a){}void f(){cout<<a<<endl<<*b<<endl<<n<<endl<<*m<<endl;}private:int a=3;int *b=&a;int n;int *m;};int main(){cls m;m.f();return 0;}*//*#include<iostream>using namespace std;struct sampleStruct{char flag[3];short value;};union sampleUnion{char flag[3];short value;};int main(){cout<<sizeof(sampleStruct)<<" "<<sizeof(sampleUnion);}//输出结果是：6，4//字符类型占1字节， 可以从任何地址开始//short类型占2字节， 必须从2字节倍数地址开始//int类型占4字节，必须从4字节倍数地址开始//0000  a[0]//0001  a[1]//0002  a[2]//0003  空一个字节//0004 b 这个是2倍数的地址//0005//结构体在内存组织上是顺序式的，联合体则是重叠式，各成员共享一段内存，所以整个联合体的sizeof也就是每个成员sizeof的最大值。*/