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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 contain a
     colon-separated list of directory paths, which can be absolute or relative to the current working
     directory.

     When path does not contain a slash character (i.e. it is just a leaf name), dlopen() searches the fol-lowing following
     lowing until it finds a compatible Mach-O file: $LD_LIBRARY_PATH, $DYLD_LIBRARY_PATH, current working
     directory, $DYLD_FALLBACK_LIBRARY_PATH.

     When path looks like a framework path (e.g. /stuff/foo.framework/foo), dlopen() searches the following
     until it finds a compatible Mach-O file: $DYLD_FRAMEWORK_PATH (with framework partial path from path ),
     then the supplied path (using current working directory for relative paths), then $DYLD_FALLBACK_FRAME-WORK_PATH $DYLD_FALLBACK_FRAMEWORK_PATH
     WORK_PATH (with framework partial path from path ).

     When path contains a slash but is not a framework path (i.e. a full path or a partial path to a dylib),
     dlopen() searches the following until it finds a compatible Mach-O file: $DYLD_LIBRARY_PATH (with leaf
     name from path ), then the supplied path (using current working directory for relative paths), then
     $DYLD_FALLBACK_LIBRARY_PATH (with leaf name from path ).

     Note: If DYLD_FALLBACK_LIBRARY_PATH is not set, dlopen operates as if DYLD_FALLBACK_LIBRARY_PATH was
     set to $HOME/lib:/usr/local/lib:/usr/lib.

     Note: If DYLD_FALLBACK_FRAMEWORK_PATH is not set, dlopen operates as if DYLD_FALLBACK_FRAMEWORK_PATH
     was set to $HOME/Library/Frameworks:/Library/Frameworks:/Network/Library/Frameworks:/Sys-tem/Library/Frameworks. $HOME/Library/Frameworks:/Library/Frameworks:/Network/Library/Frameworks:/System/Library/Frameworks.
     tem/Library/Frameworks.

     Note: There are no configuration files to control dlopen searching.

     Note: If the main executable is a set[ug]id binary or codesigned with entitlements, then all environ-ment environment
     ment 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().

SEE ALSO
     dlopen_preflight(3) dlclose(3) dlsym(3) dlerror(3) dyld(1) ld(1)

BSD                               Aug 7, 2012                              BSD

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