DLOPEN(3) BSD Library Functions Manual DLOPEN(3)NAMEdlopen — load and link a dynamic library or bundle
SYNOPSIS
#include <dlfcn.h>
void*
dlopen(const char* path, int mode);
DESCRIPTIONdlopen() examines the mach-o file specified by path. If the file is com‐
patible with the current process and has not already been loaded into the
current process, it is loaded and linked. After being linked, if it con‐
tains 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 speci‐
fied, 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 special
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.
SEARCHINGdlopen() searches for a compatible Mach-O file in the directories speci‐
fied 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 following 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_FRAMEWORK_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 rela‐
tive 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/Frame‐
works:/Library/Frameworks:/Network/Library/Frameworks:/Sys‐
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 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().
SEE ALSOdlopen_preflight(3)dlclose(3)dlsym(3)dlerror(3)dyld(1)ld(1)BSD Aug 7, 2012 BSD
