Bitwise Operators in C: AND, OR, XOR, NOT, Shifts, and Practical Bit Manipulation

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Lesson 92Mixed lesson

Bitwise Operators in C: AND, OR, XOR, NOT, Shifts, and Practical Bit Manipulation

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Lesson format12 sections1 video4 code blocks1 practice itemUpdated Aug 27, 2026

Bitwise operators work on the individual bits of integer values. AND, OR, XOR, NOT, left shift, right shift. They are the tools of flag management, permission masks, network protocol parsing, embedded register configuration, and cryptographic primitives. If you are writing systems code, you will use them daily. If you are writing application code, you will still encounter them in every header file that defines constants like O_RDONLY | O_CREAT.

Bitwise Operators

#The Six Operators#link

#include <stdio.h>

void show_bits(unsigned int val, int bits) {
    for (int i = bits - 1; i >= 0; i--) {
        printf("%d", (val >> i) & 1);
        if (i % 4 == 0 && i > 0) printf(" ");
    }
    printf("\n");
}

int main(void) {
    unsigned int a = 0b11001010;
    unsigned int b = 0b10100110;

    printf("a:       "); show_bits(a, 8);
    printf("b:       "); show_bits(b, 8);
    printf("a & b:   "); show_bits(a & b, 8);
    printf("a | b:   "); show_bits(a | b, 8);
    printf("a ^ b:   "); show_bits(a ^ b, 8);
    printf("~a:      "); show_bits(~a & 0xFF, 8);
    printf("a << 2:  "); show_bits((a << 2) & 0xFF, 8);
    printf("a >> 2:  "); show_bits(a >> 2, 8);

    return 0;
}

Run bitwise_demo

root@vulnarex:~#gcc -Wall bitwise_demo.c -o bitwise_demo && ./bitwise_demo

#Practical Use: Permission Flags#link

#include <stdio.h>

#define PERM_READ    0x04
#define PERM_WRITE   0x02
#define PERM_EXECUTE 0x01

int main(void) {
    unsigned char perms = PERM_READ | PERM_WRITE;

    printf("Permissions: 0x%02X\n", perms);
    printf("Can read:    %s\n", (perms & PERM_READ) ? "yes" : "no");
    printf("Can write:   %s\n", (perms & PERM_WRITE) ? "yes" : "no");
    printf("Can execute: %s\n", (perms & PERM_EXECUTE) ? "yes" : "no");

    perms &= ~PERM_WRITE;
    printf("\nAfter removing write: 0x%02X\n", perms);
    printf("Can write: %s\n", (perms & PERM_WRITE) ? "yes" : "no");

    return 0;
}

Run permission_flags

root@vulnarex:~#gcc -Wall permission_flags.c -o permission_flags && ./permission_flags

OR sets flags. AND tests flags. AND with NOT clears flags. XOR toggles flags. These four idioms cover every flag manipulation you will ever need. The Unix permission system, the Linux kernel's feature flags, and every hardware register interface use this pattern. Learn it until it is muscle memory.

STRICT SECURE AUDIT RULE

Right-shifting a negative signed integer is implementation-defined. Some compilers do arithmetic shift (sign-extending), others do logical shift (zero-filling). For portable bit manipulation, use unsigned types. Always.

★ 30 XP

quiz BLOCK (★ 30 XP)

What does the expression flags & ~MASK do?

Select your proof vectors above

Bitwise operators are the bridge between your C code and the hardware's binary reality. Flags, masks, shifts, and tests. Four patterns. Infinite applications. Next: the comma operator, the most misunderstood operator in C, and the only one that is almost never what you think it is.

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The Six Operators Practical Use: Permission Flags

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Last updated

August 27, 2026

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Laboratory sanity code

Isolate active probes on matched virtual networks and keep execution streams sandboxed.

#include <stdio.h>

void show_bits(unsigned int val, int bits) {

for (int i = bits - 1; i >= 0; i--) {

printf("%d", (val >> i) & 1);

if (i % 4 == 0 && i > 0) printf(" ");

}

printf("\n");

}

int main(void) {

unsigned int a = 0b11001010;

unsigned int b = 0b10100110;

printf("a: "); show_bits(a, 8);

printf("b: "); show_bits(b, 8);

printf("a & b: "); show_bits(a & b, 8);

printf("a | b: "); show_bits(a | b, 8);

printf("a ^ b: "); show_bits(a ^ b, 8);

printf("~a: "); show_bits(~a & 0xFF, 8);

printf("a << 2: "); show_bits((a << 2) & 0xFF, 8);

printf("a >> 2: "); show_bits(a >> 2, 8);

return 0;

}

#include <stdio.h>

#define PERM_READ 0x04

#define PERM_WRITE 0x02

#define PERM_EXECUTE 0x01

int main(void) {

unsigned char perms = PERM_READ | PERM_WRITE;

printf("Permissions: 0x%02X\n", perms);

printf("Can read: %s\n", (perms & PERM_READ) ? "yes" : "no");

printf("Can write: %s\n", (perms & PERM_WRITE) ? "yes" : "no");

printf("Can execute: %s\n", (perms & PERM_EXECUTE) ? "yes" : "no");

perms &= ~PERM_WRITE;

printf("\nAfter removing write: 0x%02X\n", perms);

printf("Can write: %s\n", (perms & PERM_WRITE) ? "yes" : "no");

return 0;

}