Configuring VSCode

Configuring VSCode
Visualization with Graphviz
1. Version OCaml

Compile with g++

For a file A.cpp, the simplest command in a terminal is:

make A

In VSCode, you can compile using Ctrl+B.

If we take an obviously bad code:

#include <iostream>
using namespace std;

int main(void) {
    int t[5];
    cout << t[6] << endl;
    return 0;
}

If you naively compile it, you may just get a random number displayed in your terminal.

If you click the gear after Ctrl+B, you can customize the compiler flags in tasks.json. Add the following args from AddressSanitizer:

            "-fsanitize=address",
            "-fsanitize=undefined",
            "-std=c++20",

You can also add other flags from the official SWERC command (notably the extra -Wall -Wextra):

g++ -x c++ -Wall -Wextra -g -O2 -std=gnu++20 -static -pipe A.cpp -o A

Then you should have some nice error message:

bad.cpp:7:16: runtime error: index 6 out of bounds for type 'int [5]'
bad.cpp:7:16: runtime error: load of address 0x7fffffffd5d8 with insufficient space for an object of type 'int'

Compile using clang (notably on Mac)

Unfortunately, AddressSanitizer does not work on Apple Silicon Macs. But clang may give you nice messages anyway.

If we use clangd instead, the code above will raise the following warning:

/usr/bin/clang -std=gnu++14 -fcolor-diagnostics -fansi-escape-codes -g /Users/jj/code/icpc/test.cpp -o /Users/jj/code/icpc/test
/Users/jj/code/icpc/test.cpp:6:13: warning: array index 6 is past the end of the array (that has type 'int[5]') [-Warray-bounds]
    6 |     cout << t[6] << endl;
      |             ^ ~
/Users/jj/code/icpc/test.cpp:5:5: note: array 't' declared here
    5 |     int t[5];
      |     ^
1 warning generated.

It’s also possible to download gcc on Homebrew, like g++-15, but you won’t have AddressSanitizer anyway.

Execute tests

To execute one file of testcases:

./A < A.in

To execute several files of testcases and redirect output:

for x in *in; do ./A < $x > $x.out; done
diff A.out A.in.out  # For example, or diff -y to display side by side

Competitive Programming Helper

In VSCode, install the VSCode extension cph competitive programming helper.
Download the browser extension Competitive Companion on Chrome or Firefox.
When you are on some problem statement on Kattis, click the + of the browser extension.
Go back to VSCode and choose your language (cpp) to create a new file and import the testcases from Kattis to VSCode.

Notebooks

The 25-page notebook from KTH is stress-tested, like any notebook should be.

In particular, you can check its entry about policy-based data structures.

Visualization with Graphviz

Pour visualiser un graphe, la syntaxe est la suivante :

digraph G {
    rankdir=LR;
    s -> 1 [label=1];
    s -> 2;
    1 -> 3;
    1 -> 4 [label=1];
    2 -> 4;
    3 -> t;
    4 -> t [label=1];
}

Et la commande :

dot -Tpng graph.dot > graph.png

Donne le graphe suivant :

Par exemple, ce code C++ peut faire l’affaire :

void graphviz() {
    cout << "digraph G {" << endl;
    int v;
    for(int u = 0; u < 2 * n + 2; ++u) {
        for(int i = 0; i < graph[u].size(); ++i) {
            v = graph[u][i];
            cout << u << " -> " << v << "[label=" << flow[u * SIZE + v] << "];" << endl;
        }
    }
    cout << "}" << endl;
}

En remplaçant éventuellement flow par capacity.

Version OCaml

Merci à Clémence Réda pour cette version.

(* La fonction prend en argument un graphe non orienté sous forme de liste *)
(* d'adjacence et affiche le graphe correspondant sous forme d'un code DOT *)

type graphe = int*int list array;;

let print = Printf.printf;;

let grapheno g = 
  let n=Array.length g in
  print "graph g { \n";
  for i=0 to (n-1) do
     let rec affiche liste = match liste with
      |[] -> ()
      |(b,c)::q -> print "%d -- %d [label=%d]; \n" i b c;affiche q
     in affiche g.(i);
  done;print " } \n";;

(* version orientée *)

let grapheo g = 
  let n=Array.length g in
  print "digraph g { \n";
  for i=0 to (n-1) do
     let rec affiche liste = match liste with
      |[] -> ()
      |(b,c)::q -> print "%d -> %d [label=%d]; \n" i b c;affiche q
     in affiche g.(i);
  done; print " } \n";;

(* version avec liste d'arêtes, non orienté *)

let graphelno g =
   print "graph g { \n";
   let rec affiche liste = match liste with
     |[] -> print " } \n"
     |(i,j,poids)::q -> print "%d -- %d [label=%d]; \n" i j poids;affiche q
   in affiche g;;

(* version avec liste d'arêtes, orienté *)

let graphelo g =
   print "digraph g { \n";
   let rec affiche liste = match liste with
     |[] -> print " } \n"
     |(i,j,poids)::q -> print "%d -> %d [label=%d]; \n" i j poids;affiche q
   in affiche g;;

let graphe = [(1,2,0);(3,1,0);(4,5,0);(4,8,0);(1,7,0);(1,4,0);(7,1,0);(2,4,0)];;
graphelno graphe;;