C++ Curl 后动态变量

Question

我想在 POST curl 中使用动态变量
我使用这段代码:

int send(const char*s)
{
  CURL *curl;
  CURLcode res;


  curl_global_init(CURL_GLOBAL_ALL);
  curl = curl_easy_init();
  if(curl) {
    curl_easy_setopt(curl, CURLOPT_URL, "http://localhost/query.php");
    curl_easy_setopt(curl, CURLOPT_POSTFIELDS, "q=" + s);
    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);
  }
  curl_global_cleanup();
  std::cout << std::endl << "Query sent" << std::endl;
  return 0;
}

我得到这个错误:

test.cpp:199:57: error: invalid operands of types ‘const char [3]’ and ‘const char*’ to binary ‘operator+’
         curl_easy_setopt(curl, CURLOPT_POSTFIELDS, "q=" + s);
                                                    ~~~~~^~~

Answer 1

必须自己拼接"q="和s，Cpp中没有操作符+将chars数组与指针拼接到字符。用"q="创建字符串，将s指向的数据添加到这个字符串中，调用c_str()得到const char* 指针作为 curl_easy_setopt 函数的参数:

#include <string>
....
curl_easy_setopt(curl, CURLOPT_URL, "http://localhost/query.php");
std::string buf("q=");
buf += s;
curl_easy_setopt(curl, CURLOPT_POSTFIELDS, buf.c_str());