银行家算法怎么用c语言实现

银行家算法是一种避免死锁的算法，它可以保证系统资源的安全分配。在C语言中，可以通过以下步骤实现银行家算法：

1. 定义进程数、资源数和各进程的最大需求量、已分配资源量和需求资源量等数组。
2. 定义一个可用资源向量，表示系统中可用的各类资源数量。
3. 通过输入或随机生成各数组的值。
4. 判断每个进程的需求资源量是否小于等于系统中可用的资源数量，如果是，则分配资源；否则，该进程等待。
5. 判断分配资源后是否会导致死锁，如果是，则撤销分配并回滚到之前的状态；否则，继续执行。

以下是一个简单的银行家算法的C语言实现：

#include <stdio.h>

#define MAX_PROCESS 10
#define MAX_RESOURCE 10

int available[MAX_RESOURCE];
int max[MAX_PROCESS][MAX_RESOURCE];
int allocation[MAX_PROCESS][MAX_RESOURCE];
int need[MAX_PROCESS][MAX_RESOURCE];

int n_process, n_resource;

void input_data() {
    printf("Enter number of processes: ");
    scanf("%d", &n_process);
    printf("Enter number of resources: ");
    scanf("%d", &n_resource);

    printf("Enter available resources:\n");
    for (int i = 0; i < n_resource; i++) {
        scanf("%d", &available[i]);
    }

    printf("Enter maximum demand of each process:\n");
    for (int i = 0; i < n_process; i++) {
        printf("Process %d: ", i);
        for (int j = 0; j < n_resource; j++) {
            scanf("%d", &max[i][j]);
        }
    }

    printf("Enter allocated resources of each process:\n");
    for (int i = 0; i < n_process; i++) {
        printf("Process %d: ", i);
        for (int j = 0; j < n_resource; j++) {
            scanf("%d", &allocation[i][j]);
            need[i][j] = max[i][j] - allocation[i][j];
        }
    }
}

int is_safe(int work[], int finish[]) {
    int need_copy[MAX_PROCESS][MAX_RESOURCE];
    int work_copy[MAX_RESOURCE];

    for (int i = 0; i < n_process; i++) {
        finish[i] = 0;
        for (int j = 0; j < n_resource; j++) {
            need_copy[i][j] = need[i][j];
        }
    }

    for (int i = 0; i < n_resource; i++) {
        work_copy[i] = work[i];
    }

    int count = 0;
    while (count < n_process) {
        int found = 0;
        for (int i = 0; i < n_process; i++) {
            if (!finish[i]) {
                int j;
                for (j = 0; j < n_resource; j++) {
                    if (need_copy[i][j] > work_copy[j]) {
                        break;
                    }
                }
                if (j == n_resource) {
                    for (int k = 0; k < n_resource; k++) {
                        work_copy[k] += allocation[i][k];
                    }
                    finish[i] = 1;
                    found = 1;
                    count++;
                }
            }
        }
        if (!found) {
            return 0;
        }
    }
    return 1;
}

void request_resources(int pid, int request[]) {
    int work[MAX_RESOURCE];
    int finish[MAX_PROCESS];

    for (int i = 0; i < n_resource; i++) {
        if (request[i] > need[pid][i] || request[i] > available[i]) {
            printf("Error: Requested resources exceed need or available resources.\n");
            return;
        }
    }

    for (int i = 0; i < n_resource; i++) {
        available[i] -= request[i];
        allocation[pid][i] += request[i];
        need[pid][i] -= request[i];
        work[i] = available[i];
    }

    if (is_safe(work, finish)) {
        printf("Request granted.\n");
    } else {
        printf("Request denied. Deadlock may occur.\n");
        for (int i = 0; i < n_resource; i++) {
            available[i] += request[i];
            allocation[pid][i] -= request[i];
            need[pid][i] += request[i];
        }
    }
}

int main() {
    input_data();

    int pid;
    int request[MAX_RESOURCE];

    while (1) {
        printf("Enter process ID (or -1 to exit): ");
        scanf("%d", &pid);
        if (pid == -1) {
            break;
        }
        printf("Enter resource request:\n");
        for (int i = 0; i < n_resource; i++) {
            scanf("%d", &request[i]);
        }
        request_resources(pid, request);
    }

    return 0;
}