segmentation fault

[dana18]

I don't know why is a segmentation fault error in my code .

 int nbSeqRugbyDyn(int n) {
    std::vector<int> t;
  for (int i=0; i<=n; i++) t.push_back(i);
    
    t[0]=1;
    t[1]=0;
    t[2]=0;
    t[3]=2;
    t[4]=0;
    t[5]=1;
    t[6]=4;
    t[7]=1;
    for(int i=8;i<n;i++){
        t[i]=t[i-7]+t[i-5]+2*t[i-3];
    }
    return t[n];
}

[Fanboro]

It could be n is lower than 8.

[Peter87]

Lines 5-12 will fail if n is less than 7.

[Fanboro]

If n is less than 7, this line will cause segmentation fault :
t[7] = 1;

When n is 6, the vector has 7 elements. The element t[7] does not exist.

[dana18]

int nbSeqRugbyDyn(int n) {
std::vector<int> t;
for (int i=0; i<=n; i++) t.push_back(i);
if(n==0)
return 1;
else
if(n==1)
return 0;
else
if(n==2)
return 0;
else
if(n==3)
return 2;
else
if(n==4)
return 0;
else
if(n==5)
return 1;
else
if(n==6)
return 4;
else
if(n==7)
return 1;
else
for(int i=8;i<n;i++){
t[i]=t[i-7]+t[i-5]+2*t[i-3];
}
return t[n];
}


still have the same problem

[Fanboro]

How about :

int nbSeqRugbyDyn(int n) {
std::vector<int> t;
for (int i=0; i<=n; i++) t.push_back(i);
return t[n];
}

Are you still having the same problem?

[dana18]

yes

[Voroshek]

What is the 'n'?
I have a problem if I pass char in 'n'

[dana18]

n it's an int

[Peter87]

Are you sure the segmentation fault is happening inside this function? Even if it is, it might not be what is causing it.

[dana18]

yes, I'm sure

[coder777]

The simpliest solution would be usin max(...) to adjust the vector capacity:

 int nbSeqRugbyDyn(int n) {
    std::vector<int> t;
int n1 = std::max(n, 8); // Note: n1
  for (int i=0; i<=n1; i++) t.push_back(i); // Note: use n1 here
    
    t[0]=1;
    t[1]=0;
    t[2]=0;
    t[3]=2;
    t[4]=0;
    t[5]=1;
    t[6]=4;
    t[7]=1;
    for(int i=8;i<n;i++){
        t[i]=t[i-7]+t[i-5]+2*t[i-3];
    }
    return t[n];
}

[dana18]

thank you