Tribblix: manual page: curl_global

curl_global_init(3) Introduction to Library Functions curl_global_init(3)

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.