أقنعة البت والأعلام

البتات كأعلام

#include <stdio.h>

int main(void) {
    unsigned flags = 0;
    printf("Initial flags = %u\n", flags);
    return 0;
}

تعريف الأقنعة

#include <stdio.h>

#define READ  (1u << 0)
#define WRITE (1u << 1)
#define EXEC  (1u << 2)

int main(void) {
    printf("READ=%u WRITE=%u EXEC=%u\n", READ, WRITE, EXEC);
    return 0;
}

ضبط بت

#include <stdio.h>
#define READ (1u << 0)
#define WRITE (1u << 1)

int main(void) {
    unsigned flags = 0;
    flags |= READ;
    flags |= WRITE;
    printf("flags = %u\n", flags);
    return 0;
}

مسح بت

#include <stdio.h>
#define READ (1u << 0)
#define WRITE (1u << 1)

int main(void) {
    unsigned flags = READ | WRITE;
    flags &= ~WRITE;
    printf("flags = %u\n", flags);
    return 0;
}

تبديل بت

#include <stdio.h>
#define EXEC (1u << 2)

int main(void) {
    unsigned flags = 0;
    flags ^= EXEC;
    printf("after toggle: %u\n", flags);
    flags ^= EXEC;
    printf("after toggle: %u\n", flags);
    return 0;
}

اختبار بت

#include <stdio.h>
#define READ (1u << 0)
#define WRITE (1u << 1)

int main(void) {
    unsigned flags = READ;
    if (flags & READ)  printf("READ is on\n");
    if (flags & WRITE) printf("WRITE is on\n");
    else printf("WRITE is off\n");
    return 0;
}

ضبط عدة أعلام

#include <stdio.h>
#define READ (1u << 0)
#define WRITE (1u << 1)
#define EXEC (1u << 2)

int main(void) {
    unsigned flags = READ | WRITE | EXEC;
    printf("all set: %u\n", flags);
    return 0;
}

التحقق من عدة أعلام دفعة واحدة

#include <stdio.h>
#define READ (1u << 0)
#define WRITE (1u << 1)

int main(void) {
    unsigned flags = READ | WRITE;
    unsigned need = READ | WRITE;
    if ((flags & need) == need) printf("both present\n");
    return 0;
}

طباعة الأعلام النشطة

#include <stdio.h>
#define READ (1u << 0)
#define WRITE (1u << 1)
#define EXEC (1u << 2)

int main(void) {
    unsigned flags = READ | EXEC;
    if (flags & READ)  printf("R");
    if (flags & WRITE) printf("W");
    if (flags & EXEC)  printf("X");
    printf("\n");
    return 0;
}

عدّ البتات المضبوطة

#include <stdio.h>

int main(void) {
    unsigned v = 0b10110;
    int count = 0;
    while (v) {
        v &= (v - 1);
        count++;
    }
    printf("set bits = %d\n", count);
    return 0;
}

التعدادات للأعلام

#include <stdio.h>

enum { OPT_A = 1, OPT_B = 2, OPT_C = 4 };

int main(void) {
    unsigned opts = OPT_A | OPT_C;
    printf("opts = %u\n", opts);
    if (opts & OPT_C) printf("C enabled\n");
    return 0;
}

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