为什么浮点异常？

Question

I have a floating point exception, and I don't know why.

the code is this:

void calcola_fitness(){
    vector<double> fitness;
    int n=nodes.size();
    int e=edges.size();
    int dim=feasibility.size();
    int feas=(feasibility[dim-1])*100;
    int narchi=numarchicoll[dim-1]/e;
    int numero_nodi=freePathNode.size()/n;
    double dist_start_goal=node_dist(0,1);
    int i,f,t;
    double pathlenght=0;
    int siize=freePathNode.size();
    for(i=0;i!=siize-1; i++){
        f=freePathNode[i].getIndex();
        i++;
        t=freePathNode[i].getIndex();
        i--;
        pathlenght=pathlenght+node_dist(f,t);
    }        
    double pathlenghtnorm=pathlenght/10*dist_start_goal;
    double fit=((double)numero_nodi+pathlenghtnorm+(double)narchi)*((double)feas);
    fitness.push_back(fit);
}

Could anybody help me? What's the problem? I could I solve this? thank you very much

Answer 1

"Floating point exception" (SIGFPE) is actually a misnomer. Any kinds of arithmetics exception will trigger SIGFPE. This includes divide-by-zero.

You should check if nodes and edges are empty.

Answer 2

The fastest thing you can do is using a debugger to capture the exact place where the exception is being thrown. If you are using g++ you can use gdb and make it stop in the throw:

shell$ gdb binary
(gdb) catch throw
(gdb) run

Chances are that any of the divisors in the code is 0 and that is triggering the exception, but using a debugger will tell you the exact line and you can check the variable values.

Answer 3

In your code, you have the following:

int siize=freePathNode.size();
for(i=0;i!=siize-1; i++){
    f=freePathNode[i].getIndex();
    i++;
    t=freePathNode[i].getIndex();
    i--;
    pathlenght=pathlenght+node_dist(f,t);
}

Lets assume freePathNode.size() returns 2. On the first iteration, f will be the index of element [0], and t will be the index of element [1]. That's fine. On the next iteration, f will be the index of element [1], and t will be the index of element [2], which does not exist.

So as a guess, that's where the error is coming in... you're doing a getIndex() of the end() iterator.