Merge() on two vectors crashes

[Clockowl]

Hi guys,

What am I doing wrong here? Program dies on me @ merge(). :(

#include <iostream>
#include <vector>
using namespace std;

int main() {
    int afrom[4] = {0,0,1,2};
    int ato[4] = {1,2,3,4};
    vector<int> from(&afrom[0], &afrom[4]);
    vector<int> to(&ato[0], &ato[4]);
    vector<int> length;

    vector<int> all_nodes;
    sort(from.begin(), from.end());
    sort(to.begin(), to.end());
    merge(from.begin(), from.end(), to.begin(), to.end(), all_nodes.begin());

    return 0;
}

Thanks in advance,

[Clockowl]

Ugh. Nevermind. Forgot to allocate. That's sooooooooo C. xD

(Correct?) Working code:

int main() {
    int afrom[4] = {0,0,1,2};
    int ato[4] = {1,2,3,4};
    vector<int> from(&afrom[0], &afrom[4]);
    vector<int> to(&ato[0], &ato[4]);
    vector<int> length;

    vector<int> all_nodes(from.size() + to.size());
    sort(from.begin(), from.end());
    sort(to.begin(), to.end());

    merge(from.begin(), from.end(), to.begin(), to.end(), all_nodes.begin());
    

    return 0;
}

[Narue]

all_nodes is an empty vector, merge is trying to access indices that don't exist. If you want all_nodes to be populated by std::merge, you can do it with a back_inserter:

#include <iterator>

merge(from.begin(), from.end(), to.begin(), to.end(), back_inserter(all_nodes));

Alternatively you can resize all_nodes so that you no longer overrun your memory:

vector<int> all_nodes(from.size() + to.size());

[Clockowl]

Oh that back_inserter is nice. I'm reading up on the STL as of lately, so much to learn. :D Thanks Narue.