1、使用 libcurl（推荐）

使用 libcurl 实现 HTTP GET 和 POST 请求是一种非常推荐的做法，因为 libcurl 是一个功能强大、跨平台的网络传输库，支持 HTTP、HTTPS、FTP 等多种协议。

1）GET 请求

#include <stdio.h>
#include <curl/curl.h>

// 回调函数，用于接收服务器响应数据
size_t write_callback(void *ptr, size_t size, size_t nmemb, void *userdata) {
    size_t total_size = size * nmemb;
    fwrite(ptr, size, nmemb, stdout); // 打印响应内容到控制台
    return total_size;
}

int main(void) {
    CURL *curl = curl_easy_init();
    if (curl) {
        curl_easy_setopt(curl, CURLOPT_URL, "http://httpbin.org/get");
        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_callback);

        CURLcode res = curl_easy_perform(curl); // 执行请求
        if (res != CURLE_OK) {
            fprintf(stderr, "GET request failed: %s\n", curl_easy_strerror(res));
        }

        curl_easy_cleanup(curl); // 清理资源
    }
    return 0;
}

2）POST 请求

#include <stdio.h>
#include <curl/curl.h>

size_t write_callback(void *ptr, size_t size, size_t nmemb, void *userdata) {
    size_t total_size = size * nmemb;
    fwrite(ptr, size, nmemb, stdout);
    return total_size;
}

int main(void) {
    CURL *curl = curl_easy_init();
    if (curl) {
        curl_easy_setopt(curl, CURLOPT_URL, "http://httpbin.org/post");
        curl_easy_setopt(curl, CURLOPT_POST, 1L);

        // 设置 POST 数据
        curl_easy_setopt(curl, CURLOPT_POSTFIELDS, "name=Levi&age=25");

        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_callback);

        CURLcode res = curl_easy_perform(curl);
        if (res != CURLE_OK) {
            fprintf(stderr, "POST request failed: %s\n", curl_easy_strerror(res));
        }

        curl_easy_cleanup(curl);
    }
    return 0;
}

2、使用 sockets + HTTP 手写协议

使用sockets更底层，要自己构建 HTTP 请求格式。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <netdb.h>
#include <arpa/inet.h>

#define BUFFER_SIZE 8192

void send_request(const char *host, const char *port, const char *request) {
    struct hostent *server = gethostbyname(host);
    if (!server) {
        fprintf(stderr, "ERROR: No such host\n");
        exit(1);
    }

    int sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0) {
        perror("ERROR opening socket");
        exit(1);
    }

    struct sockaddr_in serv_addr;
    memset(&serv_addr, 0, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(atoi(port));
    memcpy(&serv_addr.sin_addr.s_addr, server->h_addr, server->h_length);

    if (connect(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0) {
        perror("ERROR connecting");
        close(sockfd);
        exit(1);
    }

    send(sockfd, request, strlen(request), 0);

    char buffer[BUFFER_SIZE];
    int bytes_received;
    while ((bytes_received = recv(sockfd, buffer, sizeof(buffer) - 1, 0)) > 0) {
        buffer[bytes_received] = '\0';
        printf("%s", buffer);
    }

    close(sockfd);
}

void http_get() {
    const char *host = "httpbin.org";
    const char *port = "80";
    const char *path = "/get";

    char request[512];
    snprintf(request, sizeof(request),
             "GET %s HTTP/1.1\r\n"
             "Host: %s\r\n"
             "Connection: close\r\n"
             "\r\n",
             path, host);

    send_request(host, port, request);
}

void http_post() {
    const char *host = "httpbin.org";
    const char *port = "80";
    const char *path = "/post";
    const char *data = "name=Levi&age=30";

    char request[1024];
    snprintf(request, sizeof(request),
             "POST %s HTTP/1.1\r\n"
             "Host: %s\r\n"
             "Content-Type: application/x-www-form-urlencoded\r\n"
             "Content-Length: %zu\r\n"
             "Connection: close\r\n"
             "\r\n"
             "%s",
             path, host, strlen(data), data);

    send_request(host, port, request);
}

int main(int argc, char *argv[]) {
    if (argc != 2) {
        fprintf(stderr, "Usage: %s get|post\n", argv[0]);
        return 1;
    }

    if (strcmp(argv[1], "get") == 0) {
        http_get();
    } else if (strcmp(argv[1], "post") == 0) {
        http_post();
    } else {
        fprintf(stderr, "Unknown command: %s\n", argv[1]);
        return 1;
    }

    return 0;
}