Function to load shared libraries using a platform-portable interface.
vector of character strings specifying several short library names.
dynfind offers a platform-portable naming interface for loading a specific shared library.
The naming scheme and standard locations of shared libraries are OS-specific.
When loading a shared library dynamically at run-time across platforms via standard interfaces such as
a platform-test is usually needed to specify the OS-dependant library file path.
This library name problem is encountered via breaking up the library file path into several abstract components:
By permutation of values in each component and concatenation, a list of possible file paths can be derived.
dynfind goes through this list to try opening a library. On the first success, the search is stopped and the function returns.
Given that the three components ‘location’, ‘prefix’ and ‘suffix’ are set up properly on a per OS basis, the unique identification of a library is given by ‘libname’ - the short library name.
For some libraries, multiple ‘short library name’ are needed to make this mechanism work across all major platforms. For example, to load the Standard C Library across major R platforms:
MSVCRT.dll would be loaded;
libc.dylib on Mac OS X;
libc.so.6 on Linux and
libc.so on BSD.
Here is a sample list of values for the three other components:
‘location’: “/usr/local/lib/”, “/Windows/System32/”.
‘prefix’: “lib” (common), “” (empty - common on Windows).
‘suffix’: “.dll” (Windows), “.so” (ELF), “.dylib” (Mac OS X) and “” (empty - useful for all platforms).
The vector of ‘locations’ is initialized by environment variables such as '
PATH' on Windows and
LD_LIBRARY_PATH on Unix-flavour systems in additional to some hardcoded locations:
(The set of hardcoded locations might expand and change within the next minor releases).
The file extension depends on the OS: '
.dll' (Windows), '
.dylib' (Mac OS X), '
.so' (all others).
On Mac OS X, the search for a library includes the ‘Frameworks’ folders as well. This happens before the normal library search procedure and uses a slightly different naming pattern in a separate search phase:
|<frameworksLocation> Frameworks/ <libname> .framework/ <libname>|
The ‘frameworksLocation’ is a vector of locations such as
dynfind loads a library via
.dynload passing over the parameter
dynfind returns an external pointer (library handle), if search was successful.
Otherwise, if no library is located, a
NULL is returned.
.dynload for details on the loader interface to the OS-specific dynamic linker.
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