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carl.alv
November 21st, 2007, 12:24 PM
Hi all!

I have this function which takes as an input two arrays of vectors declared as

vector<int> v1[N], v2[N];

The function is

void fun3(Base** b, vector<int>* v1, vector<int>* v2, int N){
for(int i = 0; i < N; i++){
v1[i].clear();
v2[i].clear();
}
int cont = 0;
for(int i = 0; i < N-1; i++){
int vali = b[i]->get_priv();
for(int j = i+1; j < N; j++){
int valj = b[j]->get_priv();
int dif = vali - valj;
if(dif < 0){
v1[i].push_back(j);
cout << j << " " << v1[i][cont] << " ";
v2[j].push_back(i);
cout << i << " " << v2[j][cont] << endl;
cont++;
}
}
cout<<endl;
}
}

which for N = 4 I expect to print

1 1 0 0
2 2 0 0
3 3 0 0

2 2 1 1
3 3 1 1

3 3 2 2

1 1 0 0
2 2 0 0
3 3 0 0

2 0 1 0
3 0 1 0

3 0 2 0

I suppose that there is a memory allocation problem due to my wrong implementation of the vector array, but I don't know where is my fault. Can someone help me??

smartbei
November 21st, 2007, 12:38 PM

After the first run (which works for v1, not for v2 (it appears to, more on that in a bit)) cont = 3 right?

Now, i = 1. The problem is that the length of v1 = 1 (after the first push_back), so you are trying to access v1.

Here is how to solve. Firstly, the stl vector library provides a conveniant .at() method, which is just like brackets but imposes range safety - so if you try to access a value beyond the range of the defined vector elements it will raise an error. Use it. :)

In your case though, you can just replace cont with v1[i].size()-1, so it would be (just the interesting part):

if (dif < 0){
v1[i].push_back(j);
cout << j << " " << v1[i][v1[i].size()-1] << " ";
v2[j].push_back(i);
cout << i << " " << v2[j][v2[j].size()-1] << endl;
}

Since you just need to print the values. Note that I have not tested this - there may be syntax errors.

The reason that it appears to work on the first run for v2 is that the values are supposed to be zero anyway.

carl.alv
November 21st, 2007, 12:55 PM
Thank you for your solution smartbei!!!

hod139
November 21st, 2007, 05:08 PM
Since you have a solution, hopefully you don't mind me taking this thread off topic. Why are mixing C-style arrays with vectors? Why not use a vector of vectors? Also, why are you using C-style arrays of your class Base, and not vectors?