Unsupported Protocol using Curl in C

Question

I am currently working on a project that requires using C to make an http get request. I am trying to do this using curl. However, I get a response that says ``` error: unable to request data from https://coinex.pw/api/v2/currencies: Unsupported protocol ``` I am not sure if the error is coming from curl or from the server. Here is my code, borrowed from example code: ``` #include <curl/curl.h> static char *request(const char *url) { CURL *curl = NULL; CURLcode status; struct curl_slist *headers = NULL; char *data = NULL; long code; curl_global_init(CURL_GLOBAL_ALL); curl = curl_easy_init(); if(!curl) goto error; data = malloc(BUFFER_SIZE); if(!data) goto error; struct write_result write_result = { .data = data, .pos = 0 }; curl_easy_setopt(curl, CURLOPT_URL, url); headers = curl_slist_append(headers, "Content-type: application/json"); curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers); curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_response); curl_easy_setopt(curl, CURLOPT_WRIT…

Accepted Answer

`curl` (and `libcurl`) gives an unsupported protocol error when they can't interpret the protocol part of the URL. In your case that means `https:`, which is a bit odd.

First check you can you use the `curl` tool from the command line to retrieve the URL.

`curl -V` will give you a list of the protocols `curl` (and thus `libcurl`) will support:

```
$ curl -V
curl 7.22.0 (x86_64-pc-linux-gnu) libcurl/7.22.0 OpenSSL/1.0.1 zlib/1.2.3.4 libidn/1.23 librtmp/2.3
Protocols: dict file ftp ftps gopher http https imap imaps ldap pop3 pop3s rtmp rtsp smtp smtps telnet tftp 
Features: GSS-Negotiate IDN IPv6 Largefile NTLM NTLM_WB SSL libz TLS-SRP 
```

Check that `https` is there. It may be that your `libcurl` is not built against an SSL library or if it is that the SSL library is not installed.

Finally on this page: http://curl.haxx.se/libcurl/c/example.html you will note that is a simple https example (second one down). Please confirm that works with your `libcurl`. If so, I'd find out what your program is doing different. If not, I would find out what's wrong with your `libcurl` installation.

Unsupported Protocol using Curl in C

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