Android NDK开发(C语言--联合体与枚举)

union [union tag]
{
   member definition;
   member definition;
   ...
   member definition;
} [one or more union variables];

union Data
{
   int i;
   float f;
   char  str[20];
} data;

union Data
{
   int i;
   float f;
   char  str[20];
};
 
void main( )
{
   union Data data;        
 
   printf( "Memory size occupied by data : %d\n", sizeof(data));
 
   system("pause");
}

union  MyValue {

    int x;
    int y;
    double z;

};



void main() {

    union MyValue d1;

    d1.x = 90;

    d1.y = 100; //最后一次赋值有效

    //d1.z = 23.8;

    printf("%d , %d, %lf\n", d1.x, d1.y, d1.z);

    d1.z = 23.8;
    printf("%d, %d, %lf\n", d1.x, d1.y, d1.z);

    system("pause");

}

typedef union jvalue {
    jboolean    z;
    jbyte       b;
    jchar       c;
    jshort      s;
    jint        i;
    jlong       j;
    jfloat      f;
    jdouble     d;
    jobject     l;
} jvalue;

enum Day
{
    Monday,//默认为0，后续枚举成员的值在前一个成员上加1
    Tuesday,
    Wednesday,
    Thursday,
    Friday,
    Saturday,
    Sunday
};


void main() {
    //枚举的值，必须是括号中的值
    enum Day d = Monday;
    printf("%#x,%d\n", &d, d);

     d = Wednesday;
    printf("%#x,%d\n", &d, d);

    getchar();
}

enum Season
{
    spring, summer = 100, fall = 96, winter
};

typedef enum
{
    Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday
}
Weekday;

void main()
{
    
    printf("%d \n", spring); // 0
    printf("%d, %c \n", summer, summer); // 100, d
    printf("%d \n", fall + winter); // 193
    enum Season mySeason = winter;
    if (winter == mySeason)
        printf("mySeason is winter \n"); // mySeason is winter

    int x = 100;
    if (x == summer)
        printf("x is equal to summer\n"); // x is equal to summer

    printf("%d bytes\n", sizeof(spring)); // 4 bytes

                                          
    printf("sizeof Weekday is: %d \n", sizeof(Weekday)); //sizeof Weekday is: 4

    Weekday today = Saturday;
    Weekday tomorrow;
    if (today == Monday)
        tomorrow = Tuesday;
    else
        tomorrow = (Weekday)(today + 1); //remember to convert from int to Weekday


    getchar();
}