c和c++代码精粹 学习笔记

看了c和c++代码精粹 收益颇厚

 

// 1.0.cpp > #include < stdio.h > class  A ... {      public :       double x;       A(double d)//若explicit声明 则显示转化 f(2)改为f(A(2))        ...{                x=d;                printf("A::A ");       }} ; void  f( const  A &  a) ... {     printf("%f ",a.x); } main() ... {      A a(1);      f(a);      f(2);      getchar();} // 1.1.CPP   在任意一个转化序列里只允许一个用户定义的转换  #include < stdio.h > struct  B; struct  A ... {      public :      double x;      A(const B& b);      } ; void  f( const  A &  a) ... {     printf("%f ",a.x); }   struct  B  ... {        double y;        B(double d):y(d)        ...{                         } } ; A::A( const  B &  b):x(b.y)  ... { } int    main() ... {      A a(1);      f(a);      B b(2);     // f(3);      f(B(3));      f(A(4));      getchar();     } Z6

 

 

 

#include < iostream > #include < iomanip > #include < stdlib.h >   using   namespace  std;main() ... {      //将日期储存在一个16bit中       //法一       unsigned short date1,date,year=92,mon=8,day=2;      date=(year<<9)|(mon<<5)|day;      cout<<hex<<date<<endl;      //法二  通过位域结构实现 注意为LITTLE ENDIAN        struct Date...{             unsigned day:5;             unsigned mon:4;             unsigned year:7;      };      Date *dp=(Date *)&date1;      dp->mon=mon;      dp->day=day;      dp->year=year;      cout<<hex<<date1<<endl;                            getchar();}

 

 

 

// 1.5.CPP 预处理  #include < iostream > #include < iomanip > #include < string >  #include < stdlib.h >   using   namespace  std; #if  defined(__MSVER) < Put statement here supported by microsoft  >   #elif  defined (__BCPLUSPLUS__) < Put statement here supported by borland  >   #else   main() ... {     //RAGGED 数组       char * str[]=...{"now" ,"is","the","time"};      size_t n=sizeof str / sizeof str[0];      for(int i=0;i<n;i++)      ...{/**////还如下访问 char *p=str[0];cout<<p;  char **p =str;cout<<*(p+i)               cout<<"str"<<i<<"=="<<str[i]<<",size="<<              sizeof str[i]<<",length="<<strlen(str[i])<<endl;       }       getchar();}//#error Compiler not supported#endif

 

 

 

// 1.6.CPP 十六进制转ASCII  #include < iostream > #include < iomanip > #include < string .h >  #include < stdlib.h >  #include < stdio.h >   using   namespace  std; long  atox_ascii( char   * s) ... {    long sum;    while(isspace(*s)) s++;    for(sum=0L;isxdigit(*s);++s)    ...{         int digit;         if(isdigit(*s))         digit=*s-'0';         else digit=toupper(*s)-'A'+10;         sum=sum*16L+digit;    }    return sum;}      long  atox_allplatform( char   * s) ... {     char xdigs[]="0123456789ABCDEF";          long sum;     while(isspace(*s)) s++;     for(sum=0L;isxdigit(*s);++s)     ...{         int digit = strchr(xdigs,toupper(*s))-xdigs;         sum=sum*16L+digit;     }         return sum;} long  atox_sscanf( char   * s) ... {     long n=0L;     sscanf(s,"%x",&n);     return n; }    long  atox_great( char   * s)  ... {      return strtol(s,NULL,16); } main() ... {    cout<<atox_ascii("2a")<<endl;     cout<<atox_allplatform("2a")<<endl;     cout<<atox_sscanf("2a")<<endl;      cout<<atox_great("2a")<<endl;     getchar();}

 

 

// 1.7.CPP stdlib qsort #include < iostream > #include < iomanip > #include < string .h >  #include < stdlib.h >  #include < stdio.h >   using   namespace  std; int  comp( const   void   * p1, const   void   * p2) ... {    const int * p11= (const int *) p1;    const int * p21= (const int *) p2;    return *p11-*p21;} main() ... {           int a[]=...{34,1, 56,23};    qsort(a,sizeof a /sizeof a[0],sizeof a[0],comp);    for(int i=0;i<sizeof a /sizeof a[0];i++)    cout<<a[i]<<" ";     getchar();}