Ubuntu Manpage: curl_global_init - global libcurl initialization

Provided by: libcurl4-doc_8.9.1-2ubuntu2.1_all

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  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

       This functionality affects all supported protocols

EXAMPLE

       int main(void)
       {
         curl_global_init(CURL_GLOBAL_DEFAULT);

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

         curl_global_cleanup();
       }

AVAILABILITY

       Added in curl 7.8

RETURN VALUE

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