c语言使用函数编写程序求nl(nl=1*2*3*4*_*n)
时间: 2023-12-18 12:29:10 浏览: 25
以下是使用函数编写C语言程序求nl的例子:
```c
#include <stdio.h>
int nl(int n) {
if (n == 1) {
return 1;
} else {
return n * nl(n - 1);
}
}
int main() {
int n = 5;
printf("%d! = %d\n", n, nl(n)); // 输出:5! = 120
return 0;
}
```
相关问题
请写出netlink 非阻塞的实现程序,用C语言实现
以下是使用 epoll 实现 netlink 非阻塞通信的示例代码:
```c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <linux/netlink.h>
#include <sys/epoll.h>
#define MAX_EVENTS 10
#define NETLINK_USER 31
int main() {
int sockfd, epfd, ret;
struct sockaddr_nl src_addr, dest_addr;
struct nlmsghdr *nlh = NULL;
struct iovec iov;
struct msghdr msg;
struct epoll_event ev, events[MAX_EVENTS];
// 创建 netlink socket
sockfd = socket(PF_NETLINK, SOCK_RAW, NETLINK_USER);
if (sockfd < 0) {
perror("socket");
exit(EXIT_FAILURE);
}
// 绑定本地地址
memset(&src_addr, 0, sizeof(src_addr));
src_addr.nl_family = AF_NETLINK;
src_addr.nl_pid = getpid();
src_addr.nl_groups = 0;
if (bind(sockfd, (struct sockaddr*)&src_addr, sizeof(src_addr)) < 0) {
perror("bind");
exit(EXIT_FAILURE);
}
// 设置目标地址
memset(&dest_addr, 0, sizeof(dest_addr));
dest_addr.nl_family = AF_NETLINK;
dest_addr.nl_pid = 0; // 内核
dest_addr.nl_groups = 0;
// 初始化 netlink 消息头
nlh = (struct nlmsghdr *)malloc(NLMSG_SPACE(1024));
memset(nlh, 0, NLMSG_SPACE(1024));
nlh->nlmsg_len = NLMSG_SPACE(1024);
nlh->nlmsg_pid = getpid();
nlh->nlmsg_flags = 0;
// 设置 netlink 消息体
strcpy(NLMSG_DATA(nlh), "Hello from user space!");
// 初始化 iov 和 msg 结构体
memset(&iov, 0, sizeof(iov));
iov.iov_base = (void *)nlh;
iov.iov_len = nlh->nlmsg_len;
memset(&msg, 0, sizeof(msg));
msg.msg_name = (void *)&dest_addr;
msg.msg_namelen = sizeof(dest_addr);
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
// 发送 netlink 消息
ret = sendmsg(sockfd, &msg, 0);
if (ret < 0) {
perror("sendmsg");
exit(EXIT_FAILURE);
}
// 创建 epoll 实例
epfd = epoll_create1(0);
if (epfd < 0) {
perror("epoll_create1");
exit(EXIT_FAILURE);
}
// 将 netlink socket 注册到 epoll 实例中
ev.events = EPOLLIN | EPOLLET;
ev.data.fd = sockfd;
if (epoll_ctl(epfd, EPOLL_CTL_ADD, sockfd, &ev) < 0) {
perror("epoll_ctl");
exit(EXIT_FAILURE);
}
// 等待事件发生
while (1) {
int nfds = epoll_wait(epfd, events, MAX_EVENTS, -1);
if (nfds < 0) {
perror("epoll_wait");
exit(EXIT_FAILURE);
}
// 处理每个事件
for (int i = 0; i < nfds; i++) {
if (events[i].data.fd == sockfd) {
// 读取 netlink 消息
while (1) {
char buffer[1024];
struct nlmsghdr *nlh_recv;
struct iovec iov_recv;
struct msghdr msg_recv;
int len;
memset(&iov_recv, 0, sizeof(iov_recv));
iov_recv.iov_base = buffer;
iov_recv.iov_len = sizeof(buffer);
memset(&msg_recv, 0, sizeof(msg_recv));
msg_recv.msg_name = &src_addr;
msg_recv.msg_namelen = sizeof(src_addr);
msg_recv.msg_iov = &iov_recv;
msg_recv.msg_iovlen = 1;
len = recvmsg(sockfd, &msg_recv, MSG_DONTWAIT);
if (len < 0) {
if (errno == EAGAIN || errno == EWOULDBLOCK) {
break; // 没有更多数据了,跳出循环
}
perror("recvmsg");
exit(EXIT_FAILURE);
}
nlh_recv = (struct nlmsghdr *)buffer;
while (NLMSG_OK(nlh_recv, len)) {
if (nlh_recv->nlmsg_type == NLMSG_DONE) {
break;
}
printf("Received message: %s\n", (char*)NLMSG_DATA(nlh_recv));
nlh_recv = NLMSG_NEXT(nlh_recv, len);
}
}
}
}
}
// 关闭 socket
close(sockfd);
return 0;
}
```
该程序发送一个 netlink 消息到内核,并使用 epoll 实现非阻塞地读取内核发送的回复消息。当没有消息可读时,程序会阻塞在 epoll_wait 函数上。需要注意的是,在读取 netlink 消息时,需要通过循环来读取所有可用的消息。
写一个c语言读二进制文件通过websocket 发包函数
以下是一个简单的C语言函数,可以读取二进制文件并将其通过WebSocket发送出去:
```c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <openssl/sha.h>
#include <openssl/bio.h>
#include <openssl/evp.h>
#include <openssl/buffer.h>
#define BUF_SIZE 4096
char *base64_encode(const unsigned char *buffer, size_t length) {
BIO *bio, *b64;
BUF_MEM *bufferPtr;
b64 = BIO_new(BIO_f_base64());
bio = BIO_new(BIO_s_mem());
bio = BIO_push(b64, bio);
BIO_set_flags(bio, BIO_FLAGS_BASE64_NO_NL);
BIO_write(bio, buffer, length);
BIO_flush(bio);
BIO_get_mem_ptr(bio, &bufferPtr);
char *outputBuffer = (char *)calloc(1, bufferPtr->length + 1);
memcpy(outputBuffer, bufferPtr->data, bufferPtr->length);
outputBuffer[bufferPtr->length] = '\0';
BIO_free_all(bio);
return outputBuffer;
}
int send_file(char *filename, char *host, int port, char *path) {
FILE *fp;
char buf[BUF_SIZE];
int sock;
struct sockaddr_in serv_addr;
// 打开文件
fp = fopen(filename, "rb");
if (fp == NULL) {
perror("Error opening file");
return 1;
}
// 创建socket
sock = socket(AF_INET, SOCK_STREAM, 0);
if (sock == -1) {
perror("Error creating socket");
return 1;
}
// 设置服务器地址
memset(&serv_addr, 0, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
serv_addr.sin_addr.s_addr = inet_addr(host);
serv_addr.sin_port = htons(port);
// 连接服务器
if (connect(sock, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) == -1) {
perror("Error connecting to server");
return 1;
}
// 构造WebSocket头部
char *ws_header = "GET %s HTTP/1.1\r\n"
"Host: %s:%d\r\n"
"Upgrade: websocket\r\n"
"Connection: Upgrade\r\n"
"Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==\r\n"
"Sec-WebSocket-Version: 13\r\n\r\n";
char *request = (char *)calloc(1, strlen(path) + strlen(ws_header) + 20);
sprintf(request, ws_header, path, host, port);
// 发送WebSocket头部
send(sock, request, strlen(request), 0);
// 接收服务器返回的WebSocket头部
char response[BUF_SIZE];
recv(sock, response, BUF_SIZE, 0);
// 读取文件内容并发送
while (1) {
size_t bytes_read = fread(buf, 1, BUF_SIZE, fp);
if (bytes_read == 0) {
break;
}
// 将数据转换为WebSocket帧
unsigned char *frame = (unsigned char *)calloc(1, bytes_read + 10);
frame[0] = 0x82; // FIN + Binary
frame[1] = bytes_read;
memcpy(frame + 2, buf, bytes_read);
// 发送WebSocket帧
send(sock, frame, bytes_read + 2, 0);
free(frame);
}
// 关闭socket和文件
fclose(fp);
close(sock);
return 0;
}
int main(int argc, char *argv[]) {
if (argc != 5) {
printf("Usage: %s filename host port path\n", argv[0]);
return 1;
}
char *filename = argv[1];
char *host = argv[2];
int port = atoi(argv[3]);
char *path = argv[4];
send_file(filename, host, port, path);
return 0;
}
```
该函数使用了WebSocket协议将二进制文件发送给服务器。在函数中,我们首先打开文件,然后创建一个socket并连接到服务器。接下来,我们构造一个WebSocket头部,包含了文件内容的相关信息,并将其发送到服务器。
然后,我们读取文件内容,将其转换为WebSocket帧,并发送到服务器。最后,我们关闭socket和文件。
需要注意的是,该函数使用了OpenSSL库中的base64编码函数,因此需要在编译时链接OpenSSL库。可以使用以下命令编译该程序:
```bash
gcc send_file.c -o send_file -lssl -lcrypto
```
其中,`-lssl`和`-lcrypto`参数表示链接OpenSSL库。