How to trace a NaN in C++

Question

I am going to do some math calculations using C++ . The input floating point number is a valid number, but after the calculations, the resulting value is NaN. I would like

Answer 1

Since you mention using gdb, here's a solution that works with gcc -- you want the functions defined in fenv.h :

#define _GNU_SOURCE
#include 
#include 

int main(int argc, char **argv)
{
   double dirty = 0.0;

   feenableexcept(FE_ALL_EXCEPT & ~FE_INEXACT);  // Enable all floating point exceptions but FE_INEXACT
   double nanval=0.0/dirty;
   printf("Succeeded! dirty=%lf, nanval=%lf\n",dirty,nanval);
}

Running the above program produces the output "Floating point exception". Without the call to feenableexcept, the "Succeeded!" message is printed.

If you were to write a signal handler for SIGFPE, that might be a good place to set a breakpoint and get the traceback you want. (Disclaimer: haven't tried it!)