dlsym(3X)

NAME

dlsym − get the address of a symbol in a shared object

SYNOPSIS

cc [ flag ... ] file ... −ldl [ library ... ]

#include <dlfcn.h>

void ∗dlsym(void ∗handle, const char ∗name);

MT-LEVEL

MT-Safe

DESCRIPTION

dlsym() allows a process to obtain the address of a symbol defined within a shared object previously opened by dlopen(). handle is a value returned by a call to dlopen(); the corresponding shared object must not have been closed using dlclose(). name is the symbol’s name as a character string. dlsym() will search for the named symbol in all shared objects loaded automatically as a result of loading the object referenced by handle (see dlopen(3X)).

RETURN VALUES

If handle does not refer to a valid object opened by dlopen(), or if the named symbol cannot be found within any of the objects associated with handle, dlsym() will return NULL. More detailed diagnostic information will be available through dlerror().

EXAMPLES

The following example shows how one can use dlopen() and dlsym() to access either function 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/libx.so", 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);

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