DLOPEN(3) BSD Library Functions Manual DLOPEN(3)
NAME
dlopen -- load and link a dynamic library or bundle
SYNOPSIS
#include <dlfcn.h>
void*
dlopen(const char* path, int mode);
DESCRIPTION
dlopen() examines the mach-o file specified by path. If the file is compatible with the current
process and has not already been loaded into the current process, it is loaded and linked. After being
linked, if it contains any initializer functions, they are called, before dlopen() returns. dlopen()
can load dynamic libraries and bundles. It returns a handle that can be used with dlsym() and
dlclose(). A second call to dlopen() with the same path will return the same handle, but the internal
reference count for the handle will be incremented. Therefore all dlopen() calls should be balanced
with a dlclose() call.
If a null pointer is passed in path, dlopen() returns a handle equivalent to RTLD_DEFAULT.
mode contains options to dlopen(). It must contain one or more of the following values, possibly ORed
together:
RTLD_LAZY Each external function reference is bound the first time the function is called.
RTLD_NOW All external function references are bound immediately during the call to dlopen().
RTLD_LAZY is normally preferred, for reasons of efficiency. However, RTLD_NOW is useful to ensure that
any undefined symbols are discovered during the call to dlopen(). If neither RTLD_LAZY nor RTLD_NOW is
specified, the default is RTLD_LAZY.
One of the following flags may be ORed into the mode argument:
RTLD_GLOBAL Symbols exported from this image (dynamic library or bundle) will be available to any
images build with -flat_namespace option to ld(1) or to calls to dlsym() when using a spe-cial special
cial handle.
RTLD_LOCAL Symbols exported from this image (dynamic library or bundle) are generally hidden and only
availble to dlsym() when directly using the handle returned by this call to dlopen().
If neither RTLD_GLOBAL nor RTLD_LOCAL is specified, the default is RTLD_GLOBAL.
One of the following may be ORed into the mode argument:
RTLD_NOLOAD The specified image is not loaded. However, a valid handle is returned if the image
already exists in the process. This provides a way to query if an image is already
loaded. The handle returned is ref-counted, so you eventually need a corresponding
call to dlclose()
RTLD_NODELETE The specified image is tagged so that will never be removed from the address space,
even after all clients have released it via dlclose()
Additionally, the following may be ORed into the mode argument:
RTLD_FIRST The retuned handle is tagged so that any dlsym() calls on the handle will only search the
image specified, and not subsequent images. If path is NULL and the option RTLD_FIRST is
used, the handle returned will only search the main executable.
SEARCHING
dlopen() searches for a compatible Mach-O file in the directories specified by a set of environment
variables and the process's current working directory. When set, the environment variables must con-tain contain
tain a colon-separated list of directory paths, which can be absolute or relative to the current work-ing working
ing directory. The environment variables are LD_LIBRARY_PATH, DYLD_LIBRARY_PATH, and DYLD_FALL-BACK_LIBRARY_PATH. DYLD_FALLBACK_LIBRARY_PATH.
BACK_LIBRARY_PATH. The first two variables have no default value. The default value of DYLD_FALL-BACK_LIBRARY_PATH DYLD_FALLBACK_LIBRARY_PATH
BACK_LIBRARY_PATH is $HOME/lib;/usr/local/lib;/usr/lib. dlopen() searches the directories specified in
the environment variables in the order they are listed.
When path doesn't contain a slash character (i.e. it is just a leaf name), dlopen() searches the fol-lowing following
lowing the following until it finds a compatible Mach-O file: $LD_LIBRARY_PATH, $DYLD_LIBRARY_PATH,
current working directory, $DYLD_FALLBACK_LIBRARY_PATH.
When path contains a slash (i.e. a full path or a partial path) dlopen() searches the following the
following until it finds a compatible Mach-O file: $DYLD_LIBRARY_PATH (with leaf name from path ), cur-rent current
rent working directory (for partial paths), $DYLD_FALLBACK_LIBRARY_PATH (with leaf name from path ).
Note: There are no configuration files to control dlopen searching.
Note: If the main executable is a set[ug]id binary, then all environment variables are ignored, and
only a full path can be used.
Note: Mac OS X uses "universal" files to combine 32-bit and 64-bit libraries. This means there are no
separate 32-bit and 64-bit search paths.
RETURN VALUES
If dlopen() fails, it returns a null pointer, and sets an error condition which may be interrogated
with dlerror().
AUTHORS
Mac OS X 10.3 incorporated the dlcompat package written by Jorge Acereda <jacereda@users.source-
forge.net> and Peter O'Gorman <ogorman@users.sourceforge.net>.
In Mac OS X 10.4, dlopen was rewritten to be a native part of dyld.
SEE ALSO
dlopen_preflight(3) dlclose(3) dlsym(3) dlerror(3) dyld(3) ld(1)
BSD Nov 6, 2006 BSD
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