curl_global_init(3) Library Functions Manual 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 fea-
tures 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_ver-
sion_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 ini-
tialize 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 initial-
ization 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 initial-
ized 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 initial-
ization of Winsock has to be done by the application or you risk
getting undefined behaviors. This option exists for when the ini-
tialization 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.
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)
libcurl 2026-07-12 curl_global_init(3)
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