dyn.load {base}R Documentation

Foreign Function Interface


Load or unload shared libraries, and test whether a C function or Fortran subroutine is available.


dyn.load(x, local = TRUE, now = TRUE)

is.loaded(symbol, PACKAGE = "", type = "")


x a character string giving the pathname to a shared library or DLL.
local a logical value controlling whether the symbols in the shared library are stored in their own local table and not shared across shared libraries, or added to the global symbol table. Whether this has any effect is system-dependent.
now a logical controlling whether all symbols are resolved (and relocated) immediately the library is loaded or deferred until they are used. This control is useful for developers testing whether a library is complete and has all the necessary symbols, and for users to ignore missing symbols. Whether this has any effect is system-dependent.
symbol a character string giving a symbol name.
PACKAGE if supplied, confine the search for the name to the DLL given by this argument (plus the conventional extension, .so, .sl, .dll, ...). This is intended to add safety for packages, which can ensure by using this argument that no other package can override their external symbols. Use PACKAGE="base" for symbols linked in to R. This is used in the same way as in .C, .Call, .Fortran and .External functions
type The type of symbol to look for: can be any ("", the default), "Fortran", "Call" or "External".


See ‘See Also’ and the Writing R Extensions and R Installation and Administration manuals for how to create and install a suitable shared library. Note that unlike some versions of S-PLUS, dyn.load does not load an object (‘.o’) file but a shared library or DLL.

Unfortunately a very few platforms (Compaq Tru64) do not handle the PACKAGE argument correctly, and may incorrectly find symbols linked into R.

The additional arguments to dyn.load mirror the different aspects of the mode argument to the dlopen() routine on UNIX systems. They are available so that users can exercise greater control over the loading process for an individual library. In general, the defaults values are appropriate and you should override them only if there is good reason and you understand the implications.

The local argument allows one to control whether the symbols in the DLL being attached are visible to other DLLs. While maintaining the symbols in their own name space is good practice, the ability to share symbols across related “chapters” is useful in many cases. Additionally, on certain platforms and versions of an operating system, certain libraries must have their symbols loaded globally to successfully resolve all symbols.

One should be careful of the potential side-effect of using lazy loading via the now argument as FALSE. If a routine is called that has a missing symbol, the process will terminate immediately and unsaved session variables will be lost. The intended use is for library developers to call specify a value TRUE to check that all symbols are actually resolved and for regular users to all with FALSE so that missing symbols can be ignored and the available ones can be called.

The initial motivation for adding these was to avoid such termination in the _init() routines of the Java virtual machine library. However, symbols loaded locally may not be (read probably) available to other DLLs. Those added to the global table are available to all other elements of the application and so can be shared across two different DLLs.

Some systems do not provide (explicit) support for local/global and lazy/eager symbol resolution. This can be the source of subtle bugs. One can arrange to have warning messages emitted when unsupported options are used. This is done by setting either of the options verbose or warn to be non-zero via the options function. Currently, we know of only 2 platforms that do not provide a value for local load (RTLD_LOCAL). These are IRIX6.4 and unpatched versions of Solaris 2.5.1.

There is a short discussion of these additional arguments with some example code available at http://cm.bell-labs.com/stat/duncan/R/dynload.


The function dyn.load is used for its side effect which links the specified shared library to the executing R image. Calls to .C, .Call, .Fortran and .External can then be used to execute compiled C functions or Fortran subroutines contained in the library. The return value of dyn.load is an object of class DLLInfo. See getLoadedDLLs for information about this class.
The function dyn.unload unlinks the shared library.
is.loaded checks if the symbol name is loaded and hence available for use in .C or .Fortran or .Call or .External: it requires the name you would give to .C etc and not (as in S) that remapped by defunct functions symbol.C or symbol.For. It will succeed if any one of the four calling functions would succeed in using the entry point unless type is specified. (See .Fortran for how Fortran symbols are mapped.)


Do not use dyn.unload on a shared object loaded by library.dynam: use library.dynam.unload.


The creation of shared libraries and the runtime linking of them into executing programs is very platform dependent. In recent years there has been some simplification in the process because the C subroutine call dlopen has become the standard for doing this under UNIX. Under UNIX dyn.load uses the dlopen mechanism and should work on all platforms which support it. On Windows it uses the standard mechanisms for loading 32-bit DLLs.

The original code for loading DLLs in UNIX was provided by Heiner Schwarte. The compatibility code for HP-UX was provided by Luke Tierney.


Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.

See Also

library.dynam to be used inside a package's .First.lib initialization.

SHLIB for how to create suitable shared objects.

.C, .Fortran, .External, .Call.


is.loaded("hcass2") #-> probably TRUE, as stats is loaded
is.loaded("supsmu") # Fortran entry point in stats
is.loaded("supsmu", "stats", "Fortran")
is.loaded("PDF", type = "External")

[Package base version 2.5.0 Index]