C: الاتحادات والتعدادات

union Data {
    int i;
    float f;
    char str[4];
};

printf("%zu\n", sizeof(union Data));

4

union Data d;
d.i = 42;
printf("i = %d\n", d.i);
printf("f = %f\n", d.f);

i = 42
f = 0.000000

struct SData {
    int i;
    float f;
    char str[4];
};

union UData {
    int i;
    float f;
    char str[4];
};

printf("struct: %zu\n", sizeof(struct SData));
printf("union:  %zu\n", sizeof(union UData));

struct: 12
union:  4

typedef struct {
    int type;
    union {
        int int_val;
        float float_val;
        char str_val[32];
    } value;
} Variant;

void print_variant(const Variant *v) {
    switch (v->type) {
        case 0: printf("int: %d\n", v->value.int_val); break;
        case 1: printf("float: %f\n", v->value.float_val); break;
        case 2: printf("str: %s\n", v->value.str_val); break;
    }
}

#include <stdio.h>

typedef struct {
    int kind;
    union {
        int ival;
        double dval;
    } u;
} Number;

void print_number(const Number *n) {
    if (n->kind == 0) {
        printf("int: %d\n", n->u.ival);
    } else {
        printf("double: %.2f\n", n->u.dval);
    }
}

int main(void) {
    Number a = {0, .u.ival = 42};
    Number b = {1, .u.dval = 3.14};
    print_number(&a);
    print_number(&b);
    return 0;
}

int: 42
double: 3.14

enum Color {
    RED,
    GREEN,
    BLUE
};

enum Color favorite = GREEN;
if (favorite == GREEN) {
    printf("Green selected\n");
}

Green selected

enum Weekday {
    MON = 1,
    TUE,
    WED,
    THU,
    FRI,
    SAT = 100,
    SUN
};

printf("MON=%d SAT=%d SUN=%d\n", MON, SAT, SUN);

MON=1 SAT=100 SUN=101

enum Direction { UP, DOWN, LEFT, RIGHT };

void move(enum Direction d) {
    switch (d) {
        case UP:    printf("Move up\n"); break;
        case DOWN:  printf("Move down\n"); break;
        case LEFT:  printf("Move left\n"); break;
        case RIGHT: printf("Move right\n"); break;
    }
}

enum Status { OK = 200, NOT_FOUND = 404, ERROR = 500 };
printf("%d %d %d\n", OK, NOT_FOUND, ERROR);

200 404 500

enum Status s = OK;
int code = s;

int is_little_endian(void) {
    union {
        int i;
        char c;
    } u;
    u.i = 1;
    return u.c == 1;
}

#include <stdio.h>

typedef union {
    unsigned int i;
    unsigned char bytes[4];
} EndianTest;

void print_byte_order(void) {
    EndianTest t;
    t.i = 0x12345678;
    printf("Memory byte order: ");
    for (int i = 0; i < 4; i++) {
        printf("%02X ", t.bytes[i]);
    }
    printf("\n");
    if (t.bytes[0] == 0x78) {
        printf("Little Endian\n");
    } else {
        printf("Big Endian\n");
    }
}

int main(void) {
    print_byte_order();
    return 0;
}

Memory byte order: 78 56 34 12
Little Endian

typedef struct {
    int type;
    union {
        struct { int width, height; } rect;
        struct { int radius; } circle;
        struct { int side; } square;
    } shape;
} Figure;

Figure f;
f.type = 1;
f.shape.circle.radius = 10;