docs/libcurl/curl_global_init.md

---
c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
SPDX-License-Identifier: curl
Title: curl_global_init
Section: 3
Source: libcurl
See-also:
  - curl_easy_init (3)
  - curl_global_cleanup (3)
  - curl_global_init_mem (3)
  - curl_global_sslset (3)
  - curl_global_trace (3)
  - libcurl (3)
Protocol:
  - All
Added-in: 7.8
---

# NAME

curl_global_init - global libcurl initialization

# SYNOPSIS

~~~c
#include <curl/curl.h>

CURLcode curl_global_init(long flags);
~~~

# DESCRIPTION

This function sets up the program environment that libcurl needs. Think of it
as an extension of the library loader.

This function must be called at least once within a program (a program is all
the code that shares a memory space) before the program calls any other
function in libcurl. The environment it sets up is constant for the life of
the program and is the same for every program, so multiple calls have the same
effect as one call.

The flags option is a bit pattern that tells libcurl exactly what features to
init, as described below. Set the desired bits by ORing the values together.
In normal operation, you must specify CURL_GLOBAL_ALL. Do not use any other
value unless you are familiar with it and mean to control internal operations
of libcurl.

This function is thread-safe on most platforms. Then curl_version_info(3) has
the `threadsafe` feature set (added in 7.84.0).

If this is not thread-safe (the bit mentioned above is not set), you must not
call this function when any other thread in the program (i.e. a thread sharing
the same memory) is running. This does not just mean no other thread that is
using libcurl. Because curl_global_init(3) calls functions of other libraries
that are similarly thread unsafe, it could conflict with any other thread that
uses these other libraries.

If you are initializing libcurl from a Windows DLL you should not initialize
it from *DllMain* or a static initializer because Windows holds the loader
lock during that time and it could cause a deadlock.

See the description in libcurl(3) of global environment requirements for
details of how to use this function.

# FLAGS

## CURL_GLOBAL_ALL

Initialize everything possible. This sets all known bits except
**CURL_GLOBAL_ACK_EINTR**.

## CURL_GLOBAL_SSL

(This flag's presence or absence serves no meaning since 7.57.0. The
description below is for older libcurl versions.)

Initialize SSL.

The implication here is that if this bit is not set, the initialization of the
SSL layer needs to be done by the application or at least outside of
libcurl. The exact procedure how to do SSL initialization depends on the TLS
backend libcurl uses.

Doing TLS based transfers without having the TLS layer initialized may lead to
unexpected behaviors.

## CURL_GLOBAL_WIN32

Initialize the Win32 socket libraries.

The implication here is that if this bit is not set, the initialization of
Winsock has to be done by the application or you risk getting undefined
behaviors. This option exists for when the initialization is handled outside
of libcurl so there is no need for libcurl to do it again.

## CURL_GLOBAL_NOTHING

Initialize nothing extra. This sets no bit.

## CURL_GLOBAL_DEFAULT

A sensible default. It initializes both SSL and Win32. Right now, this equals
the functionality of the **CURL_GLOBAL_ALL** mask.

## CURL_GLOBAL_ACK_EINTR

This bit has no point since 7.69.0 but its behavior is instead the default.

Before 7.69.0: when this flag is set, curl acknowledges EINTR condition when
connecting or when waiting for data. Otherwise, curl waits until full timeout
elapses. (Added in 7.30.0)

# %PROTOCOLS%

# EXAMPLE

~~~c
int main(void)
{
  curl_global_init(CURL_GLOBAL_DEFAULT);

  /* use libcurl, then before exiting... */

  curl_global_cleanup();
}
~~~

# %AVAILABILITY%

# RETURN VALUE

If this function returns non-zero, something went wrong and you cannot use the
other curl functions.