一、介紹：

點陣圖就是用一個bit位表示一個數的存放狀態，適用於處理海量資料，可以大幅度減少空間。

二、圖解

三、程式碼實現

• BitMap.h

#ifndef __BITMAP_H__
#define __BITMAP_H__

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <string.h>

typedef struct BitMap
{
    size_t* _bits;
    size_t _range;
}BitMap;

void
 
 BitMapInit(BitMap* bm, size_t range);
void BitMapSet(BitMap* bm, size_t x);
void BitMapReset(BitMap* bm, size_t x);
int BitMapTest(BitMap* bm, size_t x);
void BitMapDestroy(BitMap* bm);

#endif __BITMAP_H__

• BitMap.c

#define _CRT_SECURE_NO_WARNINGS 1

#include "Bitmap.h"

//初始化
void BitMapInit(BitMap* bm, size_t range)
{
    assert(bm);
    bm->_range = range;
    bm->_bits = (size_t*)malloc(sizeof(size_t)*((range >> 5
 
) + 1));
    //sizeof(size_t)：每個size_t的位元組大小
    //(range >> 5) + 1：需要幾個size_t
    assert(bm->_bits);
    memset(bm->_bits, 0, sizeof(size_t)*((range >> 5) + 1));
}

//將x所在的位置置為1
void BitMapSet(BitMap* bm, size_t x)
{
    assert(bm);
    size_t index = x >> 5; //下標
    size_t num = x % 32
 
; //位置
    bm->_bits[index] |= (1 << num);
}

//將x所在的位置置為0
void BitMapReset(BitMap* bm, size_t x)
{
    assert(bm);
    size_t index = x >> 5;
    size_t num = x % 32;
    bm->_bits[index] &= ~(1 << num);
}

//檢測x是否存在
int BitMapTest(BitMap* bm, size_t x)
{
    assert(bm);
    size_t index = x >> 5;
    size_t num = x % 32;
    return ((bm->_bits[index] & (1 << num)) == 0) ? 0 : 1;
}

//銷燬
void BitMapDestroy(BitMap* bm)
{
    assert(bm);
    free(bm->_bits);
    bm->_bits = NULL;
    bm->_range = 0;
}

• Test.c

#define _CRT_SECURE_NO_WARNINGS 1

#include "Bitmap.h"

int main()
{
    BitMap bm;
    BitMapInit(&bm, 10);

    BitMapSet(&bm, 1);
    BitMapSet(&bm, 3);
    BitMapSet(&bm, 5);

    printf("%d\n", BitMapTest(&bm, 1));
    printf("%d\n", BitMapTest(&bm, 3));
    printf("%d\n", BitMapTest(&bm, 5));
    printf("%d\n", BitMapTest(&bm, 7));

    BitMapReset(&bm, 1);
    BitMapReset(&bm, 3);
    BitMapReset(&bm, 5);
    BitMapReset(&bm, 7);

    printf("%d\n", BitMapTest(&bm, 1));
    printf("%d\n", BitMapTest(&bm, 3));
    printf("%d\n", BitMapTest(&bm, 5));
    printf("%d\n", BitMapTest(&bm, 7));

    BitMapDestroy(&bm);

    system("pause");
    return 0;
}