如何c语言实现FIFO，LRU，CLOCK，OPT替换页算法，并对代码做出解释

FIFO（First-In-First-Out）算法是一种页面置换策略，它会优先淘汰最早进入内存的页面，也就是最先进入队列的页面。

下面是C语言实现FIFO算法的代码：

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

#define MAXSIZE 3  // 模拟内存中的页面数
#define PAGESIZE 10  // 每个页面的大小

typedef struct {
    int page_num;  // 页面号
    int visit_time;  // 页面最后一次访问的时间
} Page;

Page page_queue[MAXSIZE];  // 模拟内存中的页面队列
int front = 0, rear = 0;  // 队列的头和尾

// 判断页面是否在内存中
int find_page(int page_num) {
    for (int i = 0; i < rear; i++) {
        if (page_queue[i].page_num == page_num) {
            return 1;
        }
    }
    return 0;
}

// 插入新的页面
void insert_page(int page_num) {
    if (rear == MAXSIZE) {
        printf("Page Fault!\n");
        int oldest_page_index = 0;
        for (int i = 1; i < MAXSIZE; i++) {
            if (page_queue[i].visit_time < page_queue[oldest_page_index].visit_time) {
                oldest_page_index = i;
            }
        }
        printf("Page %d is replaced by Page %d\n", page_queue[oldest_page_index].page_num, page_num);
        page_queue[oldest_page_index].page_num = page_num;
        page_queue[oldest_page_index].visit_time = rear;
    } else {
        printf("Page %d is loaded into memory.\n", page_num);
        page_queue[rear].page_num = page_num;
        page_queue[rear].visit_time = rear;
        rear++;
    }
}

void handle_page_request(int page_num) {
    if (find_page(page_num)) {
        printf("Page %d is already in memory.\n", page_num);
    } else {
        insert_page(page_num);
    }
}

int main() {
    int page_requests[] = {1, 2, 3, 4, 1, 5, 6, 2, 7, 8};  // 页面请求序列
    int n = sizeof(page_requests) / sizeof(page_requests[0]);

    for (int i = 0; i < n; i++) {
        handle_page_request(page_requests[i]);
    }

    return 0;
}

LRU（Least Recently Used）算法是一种页面置换策略，它会优先淘汰最近最少使用的页面。

下面是C语言实现LRU算法的代码：

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

#define MAXSIZE 3  // 模拟内存中的页面数
#define PAGESIZE 10  // 每个页面的大小

typedef struct {
    int page_num;  // 页面号
    int visit_time;  // 页面最后一次访问的时间
} Page;

Page page_queue[MAXSIZE];  // 模拟内存中的页面队列
int front = 0, rear = 0;  // 队列的头和尾

// 判断页面是否在内存中
int find_page(int page_num) {
    for (int i = 0; i < rear; i++) {
        if (page_queue[i].page_num == page_num) {
            return 1;
        }
    }
    return 0;
}

// 插入新的页面
void insert_page(int page_num) {
    if (rear == MAXSIZE) {
        printf("Page Fault!\n");
        int least_recently_used_page_index = 0;
        for (int i = 1; i < MAXSIZE; i++) {
            if (page_queue[i].visit_time < page_queue[least_recently_used_page_index].visit_time) {
                least_recently_used_page_index = i;
            }
        }
        printf("Page %d is replaced by Page %d\n", page_queue[least_recently_used_page_index].page_num, page_num);
        page_queue[least_recently_used_page_index].page_num = page_num;
        page_queue[least_recently_used_page_index].visit_time = rear;
    } else {
        printf("Page %d is loaded into memory.\n", page_num);
        page_queue[rear].page_num = page_num;
        page_queue[rear].visit_time = rear;
        rear++;
    }
}

// 更新页面的最后一次访问时间
void update_page_visit_time(int page_num) {
    for (int i = 0; i < rear; i++) {
        if (page_queue[i].page_num == page_num) {
            page_queue[i].visit_time = rear;
            break;
        }
    }
}

void handle_page_request(int page_num) {
    if (find_page(page_num)) {
        printf("Page %d is already in memory.\n", page_num);
        update_page_visit_time(page_num);
    } else {
        insert_page(page_num);
    }
}

int main() {
    int page_requests[] = {1, 2, 3, 4, 1, 5, 6, 2, 7, 8};  // 页面请求序列
    int n = sizeof(page_requests) / sizeof(page_requests[0]);

    for (int i = 0; i < n; i++) {
        handle_page_request(page_requests[i]);
    }

    return 0;
}

CLOCK算法是一种页面置换策略，它是基于"时钟"的概念，每个页面都有一个访问位，当该页面被访问时，访问位设置为1，否则为0。算法维护一个指针，指向最近一次被访问的页面，每次淘汰页面时，从指针所指页面开始扫描，如果访问位为0，则淘汰该页面，否则将访问位设为0。

下面是C语言实现CLOCK算法的代码：

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

#define MAXSIZE 3  // 模拟内存中的页面数
#define PAGESIZE 10  // 每个页面的大小

typedef struct {
    int page_num;  // 页面号
    int reference_bit;  // 页面的访问位
} Page;

Page page_queue[MAXSIZE];  // 模拟内存中的页面队列
int front = 0, rear = 0;  // 队列的头和尾
int pointer = 0;  // 指针

// 判断页面是否在内存中
int find_page(int page_num) {
    for (int i = 0; i < rear; i++) {
        if (page_queue[i].page_num == page_num) {
            return 1;
        }
    }
    return 0;
}

// 插入新的页面
void insert_page(int page_num) {
    if (rear == MAXSIZE) {
        printf("Page Fault!\n");
        while (1) {
            if (page_queue[pointer].reference_bit == 0) {
                printf("Page %d is replaced by Page %d\n", page_queue[pointer].page_num, page_num);
                page_queue[pointer].page_num = page_num;
                page_queue[pointer].reference_bit = 1;
                pointer = (pointer + 1) % MAXSIZE;
                break;
            } else {
                page_queue[pointer].reference_bit = 0;
                pointer = (pointer + 1) % MAXSIZE;
            }
        }
    } else {
        printf("Page %d is loaded into memory.\n", page_num);
        page_queue[rear].page_num = page_num;
        page_queue[rear].reference_bit = 1;
        rear++;
    }
}

// 更新页面的访问位
void update_page_reference_bit(int page_num) {
    for (int i = 0; i < rear; i++) {
        if (page_queue[i].page_num == page_num) {
            page_queue[i].reference_bit = 1;
            break;
        }
    }
}

void handle_page_request(int page_num) {
    if (find_page(page_num)) {
        printf("Page %d is already in memory.\n", page_num);
        update_page_reference_bit(page_num);
    } else {
        insert_page(page_num);
    }
}

int main() {
    int page_requests[] = {1, 2, 3, 4, 1, 5, 6, 2, 7, 8};  // 页面请求序列
    int n = sizeof(page_requests) / sizeof(page_requests[0]);

    for (int i = 0; i < n; i++) {
        handle_page_request(page_requests[i]);
    }

    return 0;
}

OPT（Optimal）算法是一种页面置换策略，它会淘汰未来最长时间不会被访问的页面。

下面是C语言实现OPT算法的代码：

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

#define MAXSIZE 3  // 模拟内存中的页面数
#define PAGESIZE 10  // 每个页面的大小

typedef struct {
    int page_num;  // 页面号
    int next_use_time;  // 页面下一次被访问的时间
} Page;

Page page_queue[MAXSIZE];  // 模拟内存中的页面队列
int front = 0, rear = 0;  // 队列的头和尾

// 判断页面是否在内存中
int find_page(int page_num) {
    for (int i = 0; i < rear; i++) {
        if (page_queue[i].page_num == page_num) {
            return 1;
        }
    }
    return 0;
}

// 插入新的页面
void insert_page(int page_num, int next_use_time) {
    if (rear == MAXSIZE) {
        printf("Page Fault!\n");
        int farthest_page_index = 0;
        for (int i = 1; i < MAXSIZE; i++) {
            if (page_queue[i].next_use_time > page_queue[farthest_page_index].next_use_time) {
                farthest_page_index = i;
            }
        }
        printf("Page %d is replaced by Page %d\n", page_queue[farthest_page_index].page_num, page_num);
        page_queue[farthest_page_index].page_num = page_num;
        page_queue[farthest_page_index].next_use_time = next_use_time;
    } else {
        printf("Page %d is loaded into memory.\n", page_num);
        page_queue[rear].page_num = page_num;
        page_queue[rear].next_use_time = next_use_time;
        rear++;
    }
}

// 更新页面的下一次访问时间
void update_page_next_use_time(int page_num, int current_time, int page_requests[], int n) {
    for (int i = 0; i < rear; i++) {
        if (page_queue[i].page_num == page_num) {
            for (int j = current_time; j < n; j++) {
                if (page_requests[j] == page_num) {
                    page_queue[i].next_use_time = j;
                    break;
                }
            }
            break;
        }
    }
}

void handle_page_request(int page_num, int current_time, int page_requests[], int n) {
    if (find_page(page_num)) {
        printf("Page %d is already in memory.\n", page_num);
        update_page_next_use_time(page_num, current_time, page_requests, n);
    } else {
        int farthest_use_time = -1;
        for (int i = 0; i < rear; i++) {
            for (int j = current_time; j < n; j++) {
                if (page_queue[i].page_num == page_requests[j]) {
                    if (j > farthest_use_time) {
                        farthest_use_time = j;
                    }
                    break;
                }
            }
            if (farthest_use_time == -1) {
                break;
            }
        }
        if (farthest_use_time == -1) {
            insert_page(page_num, n);
        } else {
            insert_page(page_num, farthest_use_time);
        }
    }
}

int main() {
    int page_requests[] = {1, 2, 3, 4, 1, 5, 6, 2, 7, 8};  // 页面请求序列
    int n = sizeof(page_requests) / sizeof(page_requests[0]);

    for (int i = 0; i < n; i++) {
        handle_page_request(page_requests[i], i, page_requests, n);
    }

    return 0;
}