用c 语言写 get http 调用接口，入参是user 出参是{ "code": 600, "msg": "成功", "data": null }

可以使用libcurl库来实现http请求，以下是一个使用GET方法调用接口的示例代码，入参为user：

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

int main(void)
{
  CURL *curl;
  CURLcode res;
  char *url = "http://example.com/api?user=user";

  curl = curl_easy_init();
  if(curl) {
    curl_easy_setopt(curl, CURLOPT_URL, url);

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

    curl_easy_cleanup(curl);
  }
  return 0;
}

对于出参，可以使用cJSON库来解析返回的json字符串，以下是一个使用cJSON库解析json字符串并取出code、msg、data字段的示例代码：

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

int main(void)
{
  CURL *curl;
  CURLcode res;
  char *url = "http://example.com/api?user=user";
  char *response = "";

  curl = curl_easy_init();
  if(curl) {
    curl_easy_setopt(curl, CURLOPT_URL, url);

    res = curl_easy_perform(curl);
    if(res == CURLE_OK) {
      response = curl_easy_escape(curl, response, 0);
      cJSON *json = cJSON_Parse(response);
      if (json) {
        int code = cJSON_GetObjectItem(json, "code")->valueint;
        char *msg = cJSON_GetObjectItem(json, "msg")->valuestring;
        cJSON *data = cJSON_GetObjectItem(json, "data");

        printf("code: %d\n", code);
        printf("msg: %s\n", msg);
        if (cJSON_IsNull(data)) {
          printf("data: null\n");
        } else {
          // do something with data
        }
        cJSON_Delete(json);
      }
    } else {
      fprintf(stderr, "curl_easy_perform() failed: %s\n",
              curl_easy_strerror(res));
    }

    curl_easy_cleanup(curl);
  }
  return 0;
}