DESCRIPTION

The function dlsym() takes a "handle" of a dynamic loaded shared object returned by dlopen(3) along with a null-terminated symbol name, and returns the address where that symbol is loaded into memory. If the symbol is not found, in the specified object or any of the shared objects that were automatically loaded by dlopen(3) when that object was loaded, dlsym() returns NULL. (The search performed by dlsym() is breadth first through the dependency tree of these shared objects.)

Since the value of the symbol could actually be NULL (so that a NULL return from dlsym() need not indicate an error), the correct way to test for an error is to call dlerror(3) to clear any old error conditions, then call dlsym(), and then call dlerror(3) again, saving its return value into a variable, and check whether this saved value is not NULL.

There are two special pseudo-handles that may be specified in handle:

The function dlvsym() does the same as dlsym() but takes a version string as an additional argument.

RETURN VALUE

On success, these functions return the address associated with symbol. On failure, they return NULL; the cause of the error can be diagnosed using dlerror(3).

VERSIONS

dlsym() is present in glibc 2.0 and later. dlvsym() first appeared in glibc 2.1.

ATTRIBUTES

For an explanation of the terms used in this section, see attributes(7).

CONFORMING TO

POSIX.1-2001 describes dlsym(). The dlvsym() function is a GNU extension.

NOTES

EXAMPLE

See dlopen(3).

SEE ALSO

dl_iterate_phdr(3), dladdr(3), dlerror(3), dlinfo(3), dlopen(3), ld.so(8)