CODEWITHSUNDEEP
c++sigfpe
user2535797
user2535797

Reputation: 529

SIGFPE misdirection in c++

I'm trying to understand the strange behavior of the following program. Obviously, an overflow occurs during the definition of the global variable "bug", but the program throws a floating point exception during the innocent calculation 1.0+2.0. 

#include <iostream>
#include <cmath>
#include <fenv.h>

using namespace std;

const double bug = pow(10.0,pow(10.0,10.0));

int main(void)
{
  feenableexcept(-1);

  cout << "before" << endl;
  cout << 1.0 + 2.0 << endl;
  cout << "after" << endl;

  return 0;
}

I tried compiling it with both g++ and clang++, but got the same output in both

before
Floating point exception

Upvotes: 0

Views: 201

Answers (2)

AlexT
AlexT

Reputation: 1451

Once I encountered similar case when floating point error manifested itself at strange places. As I understood this happened because FPU status register is syncronized not during every floating point instruction so error may appear to be random. By the way, I've just compiled and started your program and it finished without any issues. My solution was to clear FPU status register after faulty calculation (of course this is hack but at that time I couldn't analize that math library).

Upvotes: 0

Pranit Kothari
Pranit Kothari

Reputation: 9841

const double bug = pow(10.0,pow(10.0,10.0)); should be used. Because pow need (double,double) argument and you are passing (int,int)

Upvotes: 1

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