该程序中的分段错误

Question

Shortly: I have two linear linked lists which represent a polynomial. I have to multiply them. I've wrote everything down here. The only problem is that I get a segmentation fault on one line ( if(n.grad<r->a.grad) - also marked in the code below).

I've tried this program in Borland and it works !

In CodeBlocks or MinGW it simply crashes.

#include <iostream>

using namespace std;

struct poli
{
    int grad;
    float coe;
};
struct Nod
{
    poli a;
    Nod *adr;
};
Nod *v,*sf,*v1,*vs,*vp;
void add_first(Nod *&v, poli n)
{
    if(v)
    {
        Nod *p;
        p=new Nod;
        p->a=n;
        p->adr=v;
        v=p;
    }
    else
    {
        v=new Nod;
        sf=v;
        v->a=n;
        v->adr=0;
    }
}
void add_last(Nod *&v, poli n)
{
    if(!v)
    {
        v=new Nod;
        v->a=n;
        v->adr=0;
    }
    else
    {
        Nod *p,*sf;
        sf=v;
        while(sf->adr)
            sf=sf->adr;
        p=new Nod;
        p->a=n;
        p->adr=0;
        sf->adr=p;
        sf=p;
    }
}
void add_before(Nod *v, int val, poli val_add)
{
    Nod *p, *q;
    if(v->a.grad==val)
    {
        p=new Nod;
        p->a=val_add;
        p->adr=v;
        v=p;
    }
    else
    {
        p=v;
        while(p->adr->a.grad!=val&&p->adr->adr)
            p=p->adr;
        if(p->adr->a.grad==val)
        {
            q=new Nod;
            q->a=val_add;
            q->adr=p->adr;
            p->adr=q;
        }
    }
}
void produs(Nod *v, Nod *v1, Nod *&vp)
{
    Nod *p,*q,*r;
    int gasit;
    poli n;
    p=v;
    while(p)
    {
        q=v1;
        while(q)
        {
            n.grad=p->a.grad+q->a.grad;
            n.coe=p->a.coe*q->a.coe;
            r=vp;
            gasit=0;
            while(r)
            {
                if(n.grad==r->a.grad)
                {
                    r->a.coe+=n.coe;
                    gasit=1;
                }
                r=r->adr;
            }
            if(!gasit)
            {
                r=vp;
                if(n.grad<r->a.grad)  /////////////// HERE I get the call stack
                    add_first(vp,n);
                else
                {
                    while(r->adr&&n.grad>r->adr->a.grad)
                        r=r->adr;
                    if(r->adr&&n.grad<r->adr->a.grad)
                        add_before(vp,r->adr->a.grad,n);
                    else
                        add_last(vp,n);
                }
            }
            q=q->adr;
        }
        p=p->adr;
    }
}
void tipar(Nod *v)
{
    Nod *p;
    p=v;
    while(p)
    {
        cout<<"+"<<p->a.coe<<"x^"<<p->a.grad;
        p=p->adr;
    }
}
int main()
{
    int n,m,i;
    poli a;
    cout<<"Cate elemente are polinomu' 1?";
    cin>>n;
    for(i=0;i<n;i++)
    {
        cout<<"Baga gradu'";
        cin>>a.grad;
        cout<<"Introdu-mi coe";
        cin>>a.coe;
        add_last(v,a);
        add_last(vs,a);
    }
    cout<<"Cate elemente are polinomu' 2?";
    cin>>m;
    for(i=0;i<m;i++)
    {
        cout<<"Baga gradu'";
        cin>>a.grad;
        cout<<"Introdu-mi coe";
        cin>>a.coe;
        add_last(v1,a);
    }
    produs(v,v1,vp);
    tipar(vp);
    return 0;
}

Here is the call stack window contents:

#0 004016C4 produs (v=0x4d25a0, v1=0x4d26b8, vp=@0x474018) at F:\Programe\ma ballz(23.02) (F:\Programe\suma polinom\main.cpp:142)
#1 004019F2 main () at F:\Programe\ma ballz(23.02) (F:\Programe\suma polinom\main.cpp:195)

Answer 1

looks like vp is NULL , or garbage, and then you do r = vp ...
Probably NULL because it didn't fall in the loop. It has a garbage value because you never initialize it with a value. You just declare it in the beginning.

Anyway you should learn to give meaningful names to your variables so it will be more readable and therefor maintainable.