CentOS 7.0 - man page for ares_library_init (centos section 3)
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ares_library_init - c-ares library initialization
int ares_library_init(int flags)
cc file.c -lcares
The ares_library_init function performs initializations internally required by the c-ares
library that must take place before any other function provided by c-ares can be used in a
This function must be called at least once within the life of a program, before the pro-
gram actually executes any other c-ares library function. Initializations done by this
function remain effective until a number of calls to ares_library_cleanup(3) equal to the
number of calls to this function are performed.
Successive calls to this function do nothing further, only the first call done when c-ares
is in an uninitialized state is actually effective.
The flags parameter is a bit pattern that tells c-ares exactly which features should be
initialized, as described below. Set the desired bits by ORing the values together. In
normal operation you should specify ARES_LIB_INIT_ALL. Don't use any other value unless
you are familiar with it and trying to control some internal c-ares feature.
This function is not thread safe. You have to call it once the program has started, but
this call must be done before the program starts any other thread. This is required to
avoid potential race conditions in library initialization, and also due to the fact that
ares_library_init(3) might call functions from other libraries that are thread unsafe, and
could conflict with any other thread that is already using these other libraries.
Win32/64 application DLLs shall not call ares_library_init(3) from the DllMain function.
Doing so will produce deadlocks and other problems.
Initialize everything possible. This sets all known bits.
Initialize Win32/64 specific libraries.
Initialize nothing extra. This sets no bit.
Upon successful completion, ares_library_init() will return 0. Otherwise, a non-zero
error number will be returned to indicate the error. Except for ares_strerror(3), you
shall not call any other c-ares function upon ares_library_init(3) failure.
This function was first introduced in c-ares version 1.7.0 along with the definition of
preprocessor symbol CARES_HAVE_ARES_LIBRARY_INIT as an indication of the availability of
this function. Its recursive behavior, which requires a matching number of calls to
ares_library_cleanup() in order to deinitialize the library, is present since c-ares ver-
sion 1.10.0. Earlier versions would deinitialize the library on the first call to
Since the introduction of this function it is absolutely mandatory to call it for any
Win32/64 program using c-ares.
Non-Win32/64 systems can still use c-ares version 1.7.0 without calling
ares_library_init(3) due to the fact that currently it is nearly a do-nothing function on
non-Win32/64 platforms at this point.
Copyright 1998 by the Massachusetts Institute of Technology.
Copyright (C) 2004-2009 by Daniel Stenberg.
19 May 2009 ARES_LIBRARY_INIT(3)
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