The Art of R Programming

15.1.4 Debugging R/C Code...........................................

Chapter 13 discussed a number of tools and methods for debugging R code.

However, the R/C interface presents an extra challenge. The problem in

using a debugging tool such as GDB here is that you must first apply it to R

itself.

The following is a walk-through of the R/C debugging steps using GDB

on our previoussd.ccode as the example.

$R-dgdb

GNU gdb 6.8-debian

...

(gdb) run

Starting program: /usr/lib/R/bin/exec/R

...

> dyn.load("sd.so")

> # hit ctrl-c here

Program received signal SIGINT, Interrupt.

0xb7ffa430 in __kernel_vsyscall ()

(gdb) b subdiag

Breakpoint 1 at 0xb77683f3: file sd.c, line 3.

(gdb) continue

Continuing.

Breakpoint 1, subdiag (m=0x92b9480, n=0x9482328, k=0x9482348, result=0x9817148)

at sd.c:3

3 int nval =*n, kval =*k;

(gdb)

So, what happened in this debugging session?

1. We launched the debugger, GDB, with R loaded into it, from a com-
   mand line in a terminal window:
   R-dgdb


2. We told GDB to run R:
   (gdb) run


3. We loaded our compiled C code into R as usual:

   
   

   dyn.load("sd.so")

   
   

   
   


4. We hit theCTRL-C interrupt key pair to pause R and put us back at the
   GDB prompt.


5. We set a breakpoint at the entry tosubdiag():
   (gdb) b subdiag

326 Chapter 15