What causes "Could not init curl " in curl/curl?

Check the curl_global_init return code and print curl_easy_strerror(result) to identify the failing subsystem

Could not init curl

Error message

Could not init curl

What it means

Printed by the url2file.c example when curl_global_init(CURL_GLOBAL_ALL) returns a value other than CURLE_OK. Unlike most examples that return the code silently, this one explicitly reports that global libcurl initialization failed before any easy handle is created. The %s placeholder is intentionally absent (no strerror used here), so it is a coarse-grained failure indicator.

Source

Thrown at docs/examples/url2file.c:59

  size_t written = fwrite(ptr, size, nmemb, (FILE *)stream);
  return written;
}

int main(int argc, const char *argv[])
{
  static const char pagefilename[] = "page.out";

  CURLcode result;
  CURL *curl;

  if(argc < 2) {
    printf("Usage: %s <URL>\n", argv[0]);
    return 1;
  }

  result = curl_global_init(CURL_GLOBAL_ALL);
  if(result != CURLE_OK) {
    fprintf(stderr, "Could not init curl\n");
    return (int)result;
  }

  /* init the curl session */
  curl = curl_easy_init();
  if(curl) {
    FILE *pagefile;

    /* set URL to get here */
    curl_easy_setopt(curl, CURLOPT_URL, argv[1]);

    /* Switch on full protocol/debug output while testing */
    curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L);

    /* disable progress meter, set to 0L to enable it */
    curl_easy_setopt(curl, CURLOPT_NOPROGRESS, 1L);

    /* send all data to this function */

View on GitHub (pinned to 527573490e)

Solutions

Check the curl_global_init return code and print curl_easy_strerror(result) to identify the failing subsystem
Ensure the libcurl shared library and its TLS backend (OpenSSL/Schannel/etc.) are present and version-matched at runtime (ldd / ldd-path on the binary)
Make sure curl_global_init is called exactly once before any easy handle and curl_global_cleanup only at shutdown
Reinstall/rebuild libcurl consistently (matching headers and library) if an ABI mismatch is suspected

Example fix

// before
result = curl_global_init(CURL_GLOBAL_ALL);
if(result != CURLE_OK) {
  fprintf(stderr, "Could not init curl\n");
  return (int)result;
}

// after: report the actual libcurl error for diagnosis
result = curl_global_init(CURL_GLOBAL_ALL);
if(result != CURLE_OK) {
  fprintf(stderr, "Could not init curl: %s\n", curl_easy_strerror(result));
  return (int)result;
}

Defensive patterns

Strategy: try-catch

Validate before calling

/* Guarantee curl_global_init() ran exactly once before easy_init(). */
static int g_inited = 0;
static int ensure_curl_init(void) {
  if (g_inited) return 1;
  if (curl_global_init(CURL_GLOBAL_DEFAULT) != CURLE_OK) return 0;
  g_inited = 1;
  atexit(curl_global_cleanup);
  return 1;
}
if (!ensure_curl_init()) {
  fprintf(stderr, "curl_global_init failed; cannot init curl\n");
  exit(EXIT_FAILURE);
}
CURL *c = curl_easy_init();
if (!c) { fprintf(stderr, "Could not init curl\n"); exit(EXIT_FAILURE); }

Type guard

/* Carry the non-null easy handle through a typed pointer so NULL is impossible downstream. */
typedef struct { CURL *easy; int valid; } easy_handle_t;
static easy_handle_t make_easy(void) {
  easy_handle_t h = { NULL, 0 };
  if (ensure_curl_init()) { h.easy = curl_easy_init(); h.valid = (h.easy != NULL); }
  return h;
}

Try / catch

easy_handle_t h = make_easy();
if (!h.valid) {
  fprintf(stderr, "Could not init curl\n");
  return EXIT_FAILURE;          /* nothing to cleanup: easy_init itself failed */
}
/* ... use h.easy ... */
curl_easy_cleanup(h.easy);

Prevention

Call curl_global_init() exactly once at program start (it is NOT thread-safe and not idempotent); a missing or failed global init is the usual cause of curl_easy_init() returning NULL.
Do not call any libcurl function before global init in multi-threaded code — initialize in main() before spawning threads.
Check the return of curl_global_init() before calling curl_easy_init(); treat NULL from easy_init as fatal, not as a retryable network error.
If you link libcurl statically, confirm the TLS backend was initialized at build; a backend mismatch can make init fail.

When it happens

Trigger: curl_global_init(CURL_GLOBAL_ALL) fails at process startup, which can occur when libcurl cannot initialize a subsystem (e.g. SSL backend) or when the function is called in an environment where the loaded libcurl is broken/incompatible.

Common situations: Linking against a libcurl whose required TLS backend DLL/shared library is missing or version-mismatched; calling the function after another part of the program already initialized or cleaned up libcurl; a corrupted/partial libcurl install; ABI mismatch between headers used to compile and the shared library present at runtime.

Related errors

AI-assisted analysis of curl/curl@527573490e (2026-08-01). Data as JSON: /data/errors/0c393ec60cce7464.json. Report an issue: GitHub.