[R] dyn.load() error: bad external relocation length

[Duncan Temple Lang]

Hi Walton.

.C/.Call are interfaces to _compiled_ C routines in a dynamically
loaded library (DLL or DSO - shared object).  A progra
A program is often created from compiling C code into an executable.
We can call the executable via system, but we cannot access its routines 
via .C/.Call.

So, if you have C code, use R CMD SHLIB to compile it into a loadable
libray and use dyn.load() to load it. Putting the code in the src/ 
directory of a package makes the need to do this less explicit.

But if you want to use system(), again it can be done "portably" in a 
package.
Arrange that the package creates and puts the executable in
the package's installed area.  Arrange that the program is
put in, say, inst/bin within the package and then it will be installed 
into the bin/ directory of the package. Then you can access it with

    system.file("bin", "myProg", package = "myPackageName")

and you can use that in your call to system().

The down side is that you will have to ensure that the program is built
in a portable way. So if you won the C code, it is almost the same thing
as building a DLL and using .C/.Call.

HTH

   D.



Walton A. Green wrote:
> R-helpers,
> 
> Is there an easy way to call an external (C) program using .C or .Call 
> without including the code in a package. I know how to do it using 
> system(), but that doesn't seem to be a permanent or portable solution. 
> Initially I tried:
> 
> .Call('filepath.to.c.function', arg1)
> 
> and got this error:
> 
> Error in .Call("filepath.to.c.function", "arg1",  : 
> 	"C" function name not in load table
> 
> So read the section on foreign language interfaces in the Writing R 
> Extensions manual but when I tried:
> 
> dyn.load('filepath.to.c.function')
> 
> I got:
> 
> Error in dyn.load(x, as.logical(local), as.logical(now)) : 
> 	unable to load shared library 'filepath.to.c.function':
>   dlopen(filepath.to.c.function, 6): bad external relocation length
> 
> Do you need to run R_registerRoutines before dyn.load()? I couldn't find 
> any mention of this error on the web....
> 
> Walton
> 
> platform powerpc-apple-darwin7.9.0
> arch     powerpc                  
> os       darwin7.9.0              
> system   powerpc, darwin7.9.0     
> status                            
> major    2                        
> minor    1.1                      
> year     2005                     
> month    06                       
> day      20                       
> language R
> 
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