dlsym(3C)																 dlsym(3C)

NAME

       dlsym - get the address of a symbol in a shared object or executable

SYNOPSIS

       #include <dlfcn.h>

       void *dlsym(void *restrict handle, const char *restrict name);

       The  dlsym()  function  allows a process to obtain the address of a symbol that is defined within a shared object or executable. The handle
       argument is either the value returned from a call to dlopen() or one of a family of special handles. The name argument is the symbol's name
       as a character string.

       If  handle is returned from dlopen(), the associated shared object must not have been closed using dlclose(). A handle can be obtained from
       dlopen() using the RTLD_FIRST mode. With this mode, the dlsym() function searches for the named symbol in the initial object referenced	by
       handle.	Without  this  mode,  the  dlsym() function searches for the named symbol in the group of shared objects loaded automatically as a
       result of loading the object referenced by handle. See dlopen(3C) and .

       The following special handles are supported.

       RTLD_DEFAULT

	   Instructs dlsym() to search for the named symbol starting with the first object loaded, typically the dynamic  executable.  The  search
	   continues  through the list of initial dependencies that are loaded with the process, followed by any objects obtained with dlopen(3C).
	   This search follows the default model that is used to relocate all objects within the process.

	   This model also provides for transitioning into a lazy loading environment. If a symbol can	not  be  found	in  the  presently  loaded
	   objects,  any  pending  lazy loaded objects are processed in an attempt to locate the symbol. This loading compensates for objects that
	   have not fully defined their dependencies.  However, this compensation can undermine the advantages of lazy loading.

       RTLD_PROBE

	   Instructs dlsym() to search for the named symbol in the same manner as occurs with a handle of RTLD_DEFAULT. However, this  model  only
	   searches  for symbols in the presently loaded objects, together with any lazy loadable objects specifically identified by the caller to
	   provide the named symbol. This handle does not trigger an exhaustive load of any lazy loadable symbols in an attempt to find the  named
	   symbol. This handle can provide a more optimal search than would occur using RTLD_DEFAULT.

       RTLD_NEXT

	   Instructs  dlsym()  to  search for the named symbol in the objects that were loaded following the object from which the dlsym() call is
	   being made.

       RTLD_SELF

	   Instructs dlsym() to search for the named symbol in the objects that were loaded starting with the object from which the  dlsym()  call
	   is being made.

       When used with a special handle, dlsym() is selective in searching objects that have been loaded using dlopen(). These objects are searched
       for symbols if one of the following conditions are true.

	 o  The object is part of the same local dlopen() dependency hierarchy as the calling object. See  the	 for  a  description  of  dlopen()
	    dependency hierarchies.

	 o
	    The object has global search access. See dlopen(3C) for a discussion of the RTLD_GLOBAL mode.

       The  dlsym()  function returns NULL if handle does not refer to a valid object opened by dlopen() or is not one of the special handles. The
       function also returns NULL if the named symbol cannot be found within any of the objects  associated  with  handle.  Additional	diagnostic
       information is available through dlerror(3C).

       Example 1: Use dlopen() and dlsym() to access a function or data objects.

       The  following  code fragment demonstrates how to use dlopen() and dlsym() to access either function or data objects. For simplicity, error
       checking has been omitted.

       void	 *handle;
       int	 *iptr, (*fptr)(int);

       /* open the needed object */
       handle = dlopen("/usr/home/me/libfoo.so.1", RTLD_LAZY);

       /* find the address of function and data objects */
       fptr = (int (*)(int))dlsym(handle, "my_function");
       iptr = (int *)dlsym(handle, "my_object");

       /* invoke function, passing value of integer as a parameter */
       (*fptr)(*iptr);

       Example 2: Use dlsym() to verify that a particular function is defined.

       The following code fragment shows how to use dlsym() to verify that a function is defined. If the function exists, the function is called.

       int (*fptr)();

       if ((fptr = (int (*)())dlsym(RTLD_DEFAULT,
	   "my_function")) != NULL) {
	       (*fptr)();
       }

       The dlsym() function is one of a family of functions that give the user direct access to the dynamic linking facilities.  These	facilities
       are available to dynamically-linked processes only. See the .

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Standard			   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |MT-Safe			   |
       +-----------------------------+-----------------------------+

       ld(1), ld.so.1(1), dladdr(3C), dlclose(3C), dldump(3C), dlerror(3C), dlinfo(3C), dlopen(3C), attributes(5), standards(5)

       If  an  object  is  acting  as  a  filter, care should be taken when interpreting the address of any symbol obtained using a handle to this
       object. For example, using dlsym(3C) to obtain the symbol _end for this object, results in returning the address of the symbol _end  within
       the filtee, not the filter. For more information on filters see the .

								    26 Sep 2005 							 dlsym(3C)