"undefined reference to " error when compiling C project with GNU GCC Compiler

Question

I'm hoping someone can assist. I'm new to C, and I've been experimenting with some code from the R project. The project I've created consists of a main.c file and several header files. The main.c file looks as follows:

#include "Rinternals.h"
int main(int argc, char** argv) {     
}
SEXP Cdqrls(SEXP x, SEXP y, SEXP tol, SEXP chk)
{   
SEXP ans;
SEXP qr, coefficients, residuals, effects, pivot, qraux;
int n, ny = 0, p, rank, nprotect = 4, pivoted = 0;
double rtol = asReal(tol), *work;   
}

The Rinternals.h file is this file from the R Project source: https://svn.r-project.org/R/trunk/src/include/Rinternals.h

I've included this header file in the same folder as the main.c file, and I've also included in this folder all the header files that are in the Rinternals.h #includes statements. When I attempt to compile this, I get the following error:

||=== Build: Debug in MyNewProject (compiler: GNU GCC Compiler) ===|
obj\Debug\main.o||In function `Cdqrls':|
main.c|30|undefined reference to `Rf_asReal'|

I've tried a number of things, and can't seem to find a way to get this code to compile. I'm currently working in Code::Blocks and compiling with GNU GCC Compiler. Any help with this would be greatly appreciated.

Did you remember to link with R? Merely including the header file is not enough for the compiler to link with the library. — fuz
– fuz, Commented Jan 28, 2016 at 19:08
Are you sure you want to use C, not C++ and are you sure you want to work on SEXP, not Rcpp (much easier)? And how do you compile it, from console? Because best way is to create an R package, load it in RStudio and click Build & Reload. — bartoszukm
– bartoszukm, Commented Jan 28, 2016 at 19:17

fishtank · Accepted Answer · 2016-01-28 19:18:48Z

7

You need to link it with R library (also use -I to specify include library):

cc -O2 code.c -o code -I/usr/share/R/include -L/usr/lib/R/lib -lR

answered Jan 28, 2016 at 19:18

fishtank

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