Unknown Segmentation Fault - Milk Measurement(USACO Bronze Dec. 2017)

Hi, I’m super new to C++ and I was working on the Milk Measurement problem, when I encountered the error:
run: line 1: 3 Segmentation fault (core dumped) LD_LIBRARY_PATH=/usr/local/gcc-9.2.0/lib64 ./a.out

My code is below:

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <algorithm>
#include <cmath>
#include <array>
using namespace std;
map<pair<int,int>,int> visited;
void setIO(string s) { 
vector<int> find_max(int arr[]) {
    int max = std::numeric_limits<int>::min();
    vector<int> indicies;
    for(int p = 0; p < 3;p++) {
        if(arr[p]==max) {
        else if(arr[p] > max) {
            max = arr[p];
            indicies = {arr[p]};
    return indicies;
int main() {
    // setIO("measurement");
    string names[3] = {"Bessie", "Elsie", "Mildred"};
    int production[3] = {7,7,7};
    set<string> previous_winners; set<string> cur_winners;
    // cout << (previous_winners == cur_winners);
    int l; cin >> l;
    map<int, string> day_to_name; map<int, int> day_to_change;
    int days[l];
    int counter = 0;
    for(int i = 0; i < l;i++) {
        int day;string name, change;cin >> day >> name >> change;
        days[i] = day;
        day_to_name[day] = name;
        cout << day << endl;
        if(change[0] == '+') {
            day_to_change[day] = change[1];
        else {
            day_to_change[day] = -1*(change[1]);
    sort(days, days + l);
    for(int i: days) {
        string cur_name = day_to_name[i];
        if(cur_name == "Bessie") {
            production[0] += day_to_change[i];
        else if(cur_name == "Elsie") {
            production[1] += day_to_change[i]; 
        else {
            production[2] += day_to_change[i];
        vector<int> maxima = find_max(production);
        for(int j: maxima) {
        if(cur_winners != previous_winners) {
        previous_winners = cur_winners;
    cout << counter;
    return 0;

The test case I am using is the sample test cast:

7 Mildred +3
4 Elsie -1
9 Mildred -1
1 Bessie +2

In my limited experience, this is probably due to some part of my code where I end up calling an index that doesn’t exist or something of the sort. From some debugging cout statements, my code stopped printing somewhere within the first for loop in main(), so the problem is(probably?) there. Where could my code be outputting this segmentation fault error?

Why not just continue to spit random stuff out to cout until you find the problem?

That’s kinda what I did, from using cout, I can see that my code stops working after/on the L-th iteration of the first for-loop in `main. However, I can’t see any visible problem with my code there and I feel that my code is erroring out from something that I am unfamiliar with in C++. I also edited my post to include the sample test case.

Then why not do some more printing to cout so you can see exactly where it segfaults?

I can’t print any more stuff to cout. And from what I can see from cout, I cannot determine what my problem is, which is why I’m posting to this forum.

Why can’t you print any more stuff to cout? Also, have you tried a debugger?

1 Like

I just tried a debugger, was finally able to figure out my problem. Curiously, my problem occurred after my cout statements stopped printing. Not sure why that would be the case though.