dlsym man page on HP-UX

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dlsym(3C)							     dlsym(3C)

       dlsym() - get the address of a symbol in shared library

       [flag]...  file...  [library]...

   Multithread Usage
       This routine is thread-safe.

       is  one of a family of routines that give the user direct access to the
       dynamic linking facilities (using the option on the compiler or command
       line).	allows	a  process  to	obtain the address of a symbol defined
       within a shared object previously opened by  handle  is	a  either  the
       value returned by a call to or one of the special flags and In the for‐
       mer case, the corresponding shared object must  not  have  been	closed
       using name is the symbol's name as a character string.

       searches	 for  the  named symbol in all shared objects loaded automati‐
       cally as a result of loading  the  object  referenced  by  handle  (see

       If  handle is the search begins with the "next" object after the object
       from which was invoked.	Objects are searched using a load order symbol
       resolution  algorithm  (see  dlopen(3C)).   The	"next" object, and all
       other objects searched, are either of global scope (because  they  were
       loaded  at  startup  or	as  part  of a operation with the flag) or are
       objects loaded by the same operation that loaded the caller of

       If handle is the search begins with the object from which was  invoked.
       Objects are searched using the load order symbol resolution algorithm.

       If  handle is then the symbol search is done in the scope of the object
       that invoked For example, if the caller object was loaded as  a	result
       of  with	 (see  dlopen(3C)), it does not search symbols in objects that
       were not loaded in same invocation as the caller object.

       If handle does not refer to a valid object opened by or	if  the	 named
       symbol  cannot  be found within any of the objects associated with han‐
       dle, returns NULL.  More detailed diagnostic information	 is  available

       If fails, a subsequent call to returns one of the following values:
	      Cannot apply relocation in library.

	      Internal error encountered in


	      End of liblist, invalid argument.

	      Out of memory.

	      failed on entry to or exit from

	      failed on exit from

	      failed on entry to

	      Unknown symbol.

       can  be used to navigate an intentionally created hierarchy of multiply
       defined symbols created through interposition.  For example, if a  pro‐
       gram  wished  to create an implementation of that embedded some statis‐
       tics gathering about memory allocations, such an	 implementation	 could
       define  its  own	 which would gather the necessary information, and use
       with to find the "real" which would perform the actual  memory  alloca‐
       tion.   Of  course, this "real" could be another user-defined interface
       that added its own value and then used to find the system

       The following example shows how you can use and to access either	 func‐
       tion or data objects.  For simplicity, error checking has been omitted.

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

		 /* open the needed object */
		 handle = dlopen("/usr/mydir/mylib.sl", RTLD_LAZY);

		 /* find address of function and data objects */
		 fptr = (int (*)(int))dlsym(handle, "some_function");

		 iptr = (int *)dlsym(handle, "int_object");

		 /* invoke function, passing value of integer as a parameter */

		 i = (*fptr)(*iptr);

       The  next example shows how one can use with to add functionality to an
       existing interface.  Again, error checking has been omitted.

		 extern void record_malloc(void *, size_t);

		 void *
		 malloc(size_t sz)
		       void *ptr;
		       void *(*real_malloc)(size_t);

		       real_malloc = (void * (*) (size_t))
				      dlsym(RTLD_NEXT, "malloc");
		       ptr = (*real_malloc)(sz);
		       record_malloc(ptr, sz);
		       return ptr;

       dlclose(3C), dlerrno(3C), dlerror(3C), dlopen(3C).

   Texts and Tutorials
       (See the		 option)
       (See		 manuals(5) for ordering information)


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