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 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.

SEARCHING
dlopen() uses a series of steps to find a compatible mach-o file. The first compatible file found is used.

1) If the directory specified by path does not contain a slash '/' (i.e. it is a leaf name) then the environment variable LD_LIBRARY_PATH is used. LD_LIBRARY_PATH should be a colon seperated list of directories. dlopen() searches each directory, in the order specified, for the leaf name path.

2) If DYLD_LIBRARY_PATH is set, then those directories are searched, in order, with the leaf name of path.

3) If DYLD_FALLBACK_LIBRARY_PATH is set, then those directories are searched, in order with the leaf name of path. If DYLD_FALLBACK_LIBRARY_PATH is not set, then the following directories are searched: $HOME/lib, /usr/local/lib, /usr/lib

4) Lastly, path is tried as-is as a regular file path. That means it might resolve relative to the current working directory.

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

Note: Mac OS X uses "fat" 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.sourceforge.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
dlclose(3) dlsym(3) dlerror(3) dyld(3) ld(1)