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DLSYM(3)                 BSD Library Functions Manual                 DLSYM(3)

NAME
     dlsym -- get address of a symbol

SYNOPSIS
     #include <dlfcn.h>

     void*
     dlsym(void* handle, const char* symbol);

DESCRIPTION
     dlsym() returns the address of the code or data location specified by the null-terminated character
     string symbol.  Which libraries and bundles are searched depends on the handle parameter.

     If dlsym() is called with a handle, returned by dlopen() then only that image and any libraries it
     depends on are searched for symbol.

     If dlsym() is called with the special handle RTLD_DEFAULT, then all mach-o images in the process
     (except those loaded with dlopen(xxx, RTLD_LOCAL)) are searched in the order they were loaded.  This
     can be a costly search and should be avoided.

     If dlsym() is called with the special handle RTLD_NEXT, then dyld searches for the symbol in the dylibs
     the calling image linked against when built. It is usually used when you intentionally have multiply
     defined symbol across images and want to find the "next" definition.  It searches other images for the
     definition that the caller would be using if it did not have a definition.  The exact search algorithm
     depends on whether the caller's image was linked -flat_namespace or -twolevel_namespace.  For flat
     linked images, the search starts in the load ordered list of all images, in the image right after the
     caller's image.  For two-level images, the search simulates how the static linker would have searched
     for the symbol when linking the caller's image.

     If dlsym() is called with the special handle RTLD_SELF, then the search for the symbol starts with the
     image that called dlsym().  If it is not found, the search continues as if RTLD_NEXT was used.

     If dlsym() is called with the special handle RTLD_MAIN_ONLY, then it only searches for symbol in the
     main executable.

RETURN VALUES
     The dlsym() function returns a null pointer if the symbol cannot be found, and sets an error condition
     which may be queried with dlerror().

NOTES
     The symbol name passed to dlsym() is the name used in C source code.  For example to find the address
     of function foo(), you would pass "foo" as the symbol name.  This is unlike the older dyld APIs which
     required a leading underscore.  If you looking up a C++ symbol, you need to use the mangled C++ symbol
     name.

SEE ALSO
     dlopen (3) dlerror (3) dyld (3) ld(1) cc(1)

                                August 28, 2008