what is wrong with my code

help
1

#include
using namespace std;

int main()
{
int t,n,x,p,score;
cin>>t;

    for (int i=0;i<t;i++)
    {

            cin>>n>>x>>p;

            score=3*x-(n-x);



            if (score>=p)
            {
                    cout<<"pass"<<endl;


            }
            else{
                    cout<<"fail"<<endl;

            }






    }
    return 0;

}
~

2
2 Likes
3

(I don’t want to create another thread) How do I limit \red{\text{main memory}} to a CPP program?

I am using Ubuntu 20.04 LTS. I want to limit the memory used by CPP Programs. Currently, I am using the following command to compile and run CPP Programs.

# Compile
g++ -std=c++17 -Wshadow -Wall -Wno-unused-result -o exe -O2 <program_name.cpp>
# Run
./exe < input.txt > output.txt

PS: My laptop used to stuck for a while when I run bad CPP programs. It requires a restart to recover. I don’t want it to happen in future.

@ssjgz

1 Like
4

Thanks

5

There are polling-based “solutions” that kind of work, but are unreliable - it’s possible for an executable to gobble memory too quickly for the poll’er to spot and kill it. The way I do it is with a separate user (called luser, with his own little directly that he can read and write) and cgroups.

Create a new user whose process memory usage you want to limit (luser in my case).

Set up the config files as below:

[simon@simon-laptop][14:04:59]
[~/devel/hackerrank/otherpeoples/luser]>cat /etc/cgconfig.conf 
group memlimit {
    memory {
        memory.limit_in_bytes = 1536m;
    }
}


[simon@simon-laptop][14:05:03]
[~/devel/hackerrank/otherpeoples/luser]>cat /etc/cgrules.conf 
luser   memory   memlimit
[simon@simon-laptop][14:05:04]
[~/devel/hackerrank/otherpeoples/luser]>

and run:

sudo cgconfigparser -l /etc/cgconfig.conf
sudo cgrulesengd

(you may need to run this each time you reboot).

Then switch to luser, and try an executable that you know will gobble up more than the allotted limit (~1.5GB, in this case). I’m sure I had an example of this, but can’t find it now :stuck_out_tongue:

Edit:

Here’s a dummy example:

[luser@simon-laptop][14:36:07]
[/home/simon/devel/hackerrank/otherpeoples/luser]>cat rapid-memory-gobble.cpp 
#include <iostream>

using namespace std;

int main()
{
    while (true)
    {
        new int[10'000];
    }
}
[luser@simon-laptop][14:36:09]
[/home/simon/devel/hackerrank/otherpeoples/luser]>time -p ./a.out 
Killed
real 2.21
user 0.28
sys 1.14

Edit2:

Aha - here’s a “real-life” example, taken from here:

[luser@simon-laptop][14:47:04]
[/home/simon/devel/hackerrank/otherpeoples/luser]>../codechef-download-solution.rb https://www.codechef.com/viewsolution/49455011
Solution written to: ghanch_2021-MUFFINS3.cpp
[luser@simon-laptop][14:47:06]
[/home/simon/devel/hackerrank/otherpeoples/luser]>../compile-latest-cpp.sh 
Compiling ghanch_2021-MUFFINS3.cpp
Executing command:
  g++ -std=c++17 ghanch_2021-MUFFINS3.cpp -O3 -g3 -Wall -Wextra -Wconversion -DONLINE_JUDGE -D_GLIBCXX_DEBUG    -fsanitize=undefined -ftrapv
Successful
[luser@simon-laptop][14:47:11]
[/home/simon/devel/hackerrank/otherpeoples/luser]>ruby -e 'print "1000\n"; 1000.times { print "100000000\n" }' | time -p ./a.out 
50000001

50000001

50000001

50000001

Command terminated by signal 9
real 7.50
user 5.33
sys 1.10
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