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.\" $FreeBSD: src/lib/libc/gen/dlopen.3 211397 2010-08-16 15:18:30Z joel $
.\"
.Dd April 28, 2011
.Dt DLVSYM 3
.Os
.Sh NAME
.Nm dlsym
.Nd shared object symbol lookup by version function
.Sh LIBRARY
This function is not in a library.
It is included in every dynamically linked program automatically.
.Sh SYNOPSIS
.In dlfcn.h
.Ft void *
.Fn dlsym "void *handle" "const char *name" "const char *version"
.Ft "void *"
.Fn dlvsym "void *handle" "const char *name" "const char *version"
.Sh DESCRIPTION
The
.Fn dlvsym
function
does the same as
.Fn dlsym
but takes a version string as an additional argument.  Both the name and
the version must match in order for the symbol to be resolved.
.Sh NOTES
ELF executables need to be linked
using the
.Fl export-dynamic
option to
.Xr ld 1
for symbols defined in the executable to become visible to
.Fn dlvsym .
.Sh RETURN VALUE
The
.Fn dlvsym
function
returns the address of the symbol unless the symbol can not be found.
In this case, it returns a null pointer and sets an error condition
which may be queried with
.Fn dlerror .
.Sh EXAMPLE
The following program will obtain a pointer to the gcc library __adsvsi3
function using dlvsym specified to version GCC_3.0, and then it will use it
to print out the sum of 500 + 325.
.Bd -literal
#include <dlfcn.h>
#include <stdlib.h>
#include <stdio.h>

int
main (int argc, char *argv[])
{
    void       *handle;
    int        (*func_sum)(int a, int b);

    /* open the pkgsrc shared gcc library  */
    handle = dlopen("/usr/pkg/lib/libgcc_s.so", RTLD_LAZY);
    if (!handle) {
       fprintf (stderr, "%s\en", dlerror ());
       exit (EXIT_FAILURE);
    }

    /* get pointer to integer sum function */
    func_sum = dlvsym (handle, "__addvsi3", "GCC_3.0");
    if (func_sum == NULL) {
       fprintf (stderr, "function %s version %s not found\en",
                "__addvsi3", "GCC_3.0");
       dlclose (handle);
       exit (EXIT_FAILURE);
    }

    /* Calculate and display the sum of 500 + 325 */
    printf ("500 + 325 = %d\en", func_sum((int)500, (int)325));
    dlclose (handle);

    exit(EXIT_SUCCESS);
}
.Ed
.Sh SEE ALSO
.Xr rtld 1 ,
.Xr dlfcn 3 ,
.Xr dlsym 3 ,
.Xr dlvsym 3
.Sh HISTORY
The
.Nm
function first appeared in
.Dx 2.11 .