Json string in libcurl

Question

Can I send a Json string using libcurl. I am new to both. Any kind of help would be appreciated. Basically i want to send a Json string using libcurl simple send and receive in C

My code is below:

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

/* Auxiliary function that waits on the socket. */ 
static int wait_on_socket(curl_socket_t sockfd, int for_recv, long timeout_ms)
{
  struct timeval tv;
  fd_set infd, outfd, errfd;
  int res;

  tv.tv_sec = timeout_ms / 1000;
  tv.tv_usec= (timeout_ms % 1000) * 1000;

  FD_ZERO(&infd);
  FD_ZERO(&outfd);
  FD_ZERO(&errfd);

  FD_SET(sockfd, &errfd); /* always check for error */ 

  if(for_recv)
  {
    FD_SET(sockfd, &infd);
  }
  else
  {
    FD_SET(sockfd, &outfd);
  }

  /* select() returns the number of signalled sockets or -1 */ 
  res = select(sockfd + 1, &infd, &outfd, &errfd, &tv);
  return res;
}

int main(void)
{
  CURL *curl;
  CURLcode res;
  /* Minimalistic http request */ 
  const char *request = "reactantsJSON={"O=O":{"N":1}}&productsJSON=["O=O","[O]"]&temperature=2273.15&pressure=101.325";
  curl_socket_t sockfd; /* socket */ 
  long sockextr;
  size_t iolen;

  curl = curl_easy_init();
  if(curl) {
    curl_easy_setopt(curl, CURLOPT_URL, "http://gibbs.sdsu.edu:8080/axis2/services/GibbsMinimization/solveTP");
    /* Do not do the transfer - only connect to host */ 
    curl_easy_setopt(curl, CURLOPT_CONNECT_ONLY, 1L);
    res = curl_easy_perform(curl);

    if(CURLE_OK != res)
    {
      printf("Error: %s\n", strerror(res));
      return 1;
    }

    /* Extract the socket from the curl handle - we'll need it for waiting.
     * Note that this API takes a pointer to a 'long' while we use
     * curl_socket_t for sockets otherwise.
     */ 
    res = curl_easy_getinfo(curl, CURLINFO_LASTSOCKET, &sockextr);

    if(CURLE_OK != res)
    {
      printf("Error: %s\n", curl_easy_strerror(res));
      return 1;
    }

    sockfd = sockextr;

    /* wait for the socket to become ready for sending */ 
    if(!wait_on_socket(sockfd, 0, 60000L))
    {
      printf("Error: timeout.\n");
      return 1;
    }

    puts("Sending request.");
    /* Send the request. Real applications should check the iolen
     * to see if all the request has been sent */ 
    res = curl_easy_send(curl, request, strlen(request), &iolen);

    if(CURLE_OK != res)
    {
      printf("Error: %s\n", curl_easy_strerror(res));
      return 1;
    }
    puts("Reading response.");

    /* read the response */ 
    for(;;)
    {
      char buf[1024];

      wait_on_socket(sockfd, 1, 60000L);
      res = curl_easy_recv(curl, buf, 1024, &iolen);

      if(CURLE_OK != res)
        break;

      printf("Received %u bytes.\n", iolen);
    }

    /* always cleanup */ 
    curl_easy_cleanup(curl);
  }
  return 0;
}

the error I am getting is that it says a ";" is missing in line 40, which is nothing but the json string, even though I ahve a ";" on that line. It looks like to send json string i need to do something, which I am not aware of. Do I need to specify some flags while compiling the code.

What do you want to send it to? httpd? ftp server? telnet session? — Pete Wilson
– Pete Wilson, Commented Sep 8, 2011 at 16:34
@undur_gongor: gibbs.sdsu.edu:8080/axis2/services/GibbsMinimization/solveTP ----> this is my URL and the Json string i want to send is "reactantsJSON={"O=O":{"N":1}}&productsJSON=["O=O","[O]"]&temperature=2273.15&pressure=101.325". the code doesn't compile — user537670
– user537670, Commented Sep 8, 2011 at 17:43

Piotr Praszmo · Accepted Answer · 2011-09-08 17:51:47Z

3

const char *request = "reactantsJSON={"O=O":{"N":1}}&productsJSON=["O=O","[O]"]&temperature=2273.15&pressure=101.325";

You need to escape " in your string literal.

const char *request = "reactantsJSON={\"O=O\":{\"N\":1}}&productsJSON=[\"O=O\",\"[O]\"]&temperature=2273.15&pressure=101.325";

answered Sep 8, 2011 at 17:51

Piotr Praszmo

18.4k2 gold badges59 silver badges66 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Json string in libcurl

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related