windows c语言实现http下载文件

在 Windows 平台上，可以使用 Winsock 库来实现 HTTP 下载文件。以下是一个简单的 C 语言程序，演示如何实现 HTTP 下载文件：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <winsock2.h>

#define BUFFER_SIZE 1024

int main(int argc, char *argv[]) {
    if (argc < 2) {
        printf("usage: %s url\n", argv[0]);
        return 1;
    }

    // 初始化 Winsock 库
    WSADATA wsaData;
    if (WSAStartup(MAKEWORD(2, 2), &wsaData) != 0) {
        perror("WSAStartup failed");
        return 1;
    }

    // 解析 URL
    char *url = argv[1];
    char *host = strtok(url, "/");
    char *path = strtok(NULL, "");
    if (path == NULL) {
        path = "/";
    }

    // 建立 TCP 连接
    struct hostent *server = gethostbyname(host);
    if (server == NULL) {
        perror("gethostbyname failed");
        return 1;
    }
    SOCKET sockfd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (sockfd == INVALID_SOCKET) {
        perror("socket failed");
        return 1;
    }
    struct sockaddr_in addr;
    memset(&addr, 0, sizeof(addr));
    addr.sin_family = AF_INET;
    addr.sin_port = htons(80);
    memcpy(&addr.sin_addr.s_addr, server->h_addr, server->h_length);
    if (connect(sockfd, (struct sockaddr *)&addr, sizeof(addr)) == SOCKET_ERROR) {
        perror("connect failed");
        return 1;
    }

    // 发送 HTTP 请求
    char request[BUFFER_SIZE];
    sprintf(request, "GET /%s HTTP/1.1\r\nHost: %s\r\n\r\n", path, host);
    if (send(sockfd, request, strlen(request), 0) == SOCKET_ERROR) {
        perror("send failed");
        return 1;
    }

    // 接收 HTTP 响应
    char response[BUFFER_SIZE];
    int n = recv(sockfd, response, BUFFER_SIZE, 0);
    if (n == SOCKET_ERROR) {
        perror("recv failed");
        return 1;
    }
    response[n] = '\0';

    // 解析响应头
    char *content_length = strstr(response, "Content-Length:");
    if (content_length == NULL) {
        printf("unknown file size\n");
        return 1;
    }
    int file_size = atoi(content_length + strlen("Content-Length:"));
    printf("file size: %d\n", file_size);

    // 写入文件
    FILE *file = fopen("file.txt", "wb");
    char buffer[BUFFER_SIZE];
    int total = 0;
    while (total < file_size) {
        n = recv(sockfd, buffer, BUFFER_SIZE, 0);
        if (n == SOCKET_ERROR) {
            perror("recv failed");
            return 1;
        }
        fwrite(buffer, sizeof(char), n, file);
        total += n;
    }
    fclose(file);

    // 关闭连接
    closesocket(sockfd);

    // 卸载 Winsock 库
    WSACleanup();

    printf("file downloaded\n");
    return 0;
}

注意：以上代码仅供参考，实际使用时需要添加错误处理和其他必要的检查。