Simplified example using Rcpp to link an object file to a function [duplicate]

问题

I have existing C code that consists of three files: a header file ( a ".h" file), a library file (a ".o" file), and a source file. They currently run under UNIX and as compiled "mex files" in Matlab. I would like to port them to R using Rcpp. They are all long and complex, so I made a minimal example to help me understand how to port them to R.

The simplified header file (my_header.h) is:

typedef unsigned int    ui4;
ui4  add_one( ui4 );

The simplified "library" file (my_lib.cpp) is:

#include <stdlib.h>
#include <stdio.h>
#include <string.h>

#include "my_header.h"

ui4 add_one(ui4 x) {
        return(x+1);
}

The simplified function program (my_program.cpp) is:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <time.h>
#include <Rcpp.h>
#include <cmath>

#include "my_header.h"

using namespace Rcpp;

// [[Rcpp::export]]
ui4 my_program_r () {
//int main (int argc, const char * argv[]) {
//
// As a MATLAB mex file, this function calls "main(..."
//
  ui4 value = add_one( (ui4)1 );
  printf( "%d", value );
  return value;
}

From the terminal (I'm on a Mac), I can compile these without an error:

$ g++ my_lib.cpp -c -o my_lib.o
$ g++ my_program.cpp -o my_program my_lib.o

When I try to compile them in RStudio, I get:

> library(Rcpp)
> sourceCpp( "my_program.cpp" )
Warning message:
In sourceCpp("my_program.cpp") :
  No Rcpp::export attributes or RCPP_MODULE declarations found in source
>

Why isn't this compiling under Rcpp? How do I specify the linked file (the ".o" library file) in the "sourceCpp" command? Do I need to specify the header file?

回答1:

The sourceCpp command is meant for single files only. If you have multiple files, you have to use a package:

Call Rcpp::Rcpp.package.skeleton(...) to create a skeleton package.
Copy *.h, *.c and *.cpp to the src folder.
Call Rcpp::compileAtrributes().
Use R CMD build ..., R CMD check ... and R CMD INSTALL ... to build, check and compile the package. (The check will complain about undocumented functions ...)

For more details see Rcpp-package vignette and for example this question. BTW, since R does not have an unsigned int type, I am not sure if your return value will work. You might have to switch to an int or double. I also get a different error message than you:

Error in dyn.load("/tmp/RtmpSbvXHx/sourceCpp-i686-pc-linux-gnu-0.12.17/sourcecpp_625ad24a943/sourceCpp_2.so") : unable to load shared object '/tmp/RtmpSbvXHx/sourceCpp-i686-pc-linux-gnu-0.12.17/sourcecpp_625ad24a943/sourceCpp_2.so': /tmp/RtmpSbvXHx/sourceCpp-i686-pc-linux-gnu-0.12.17/sourcecpp_625ad24a943/sourceCpp_2.so: undefined symbol: _Z7add_onej

Are you sure the above code is exactly what you used?

来源：https://stackoverflow.com/questions/50770830/simplified-example-using-rcpp-to-link-an-object-file-to-a-function

标签

rcpp