Ubuntu Manpage: curl_global_init - Global libcurl initialization

NAME

       curl_global_init - Global libcurl initialization

SYNOPSIS

       #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  since  libcurl  7.84.0  if  curl_version_info(3)  has  the
       CURL_VERSION_THREADSAFE feature bit set (most platforms).

       If  this  is not thread-safe, 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's
no need for libcurl to do it again.

CURL_GLOBAL_NOTHING
Initialise nothing extra. This sets no bit.

CURL_GLOBAL_DEFAULT
A sensible default. It will init 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 will acknowledge EINTR condition when
connecting or when waiting for data. Otherwise, curl waits until full timeout
elapses. (Added in 7.30.0)

EXAMPLE

        curl_global_init(CURL_GLOBAL_DEFAULT);

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

        curl_global_cleanup();

AVAILABILITY

       Added in 7.8

RETURN VALUE

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