Customized Debugging in Sublime Text using C++ for Competitive Programming

• Competitive Programming is a mental sport that enables us to code a given problem under provided constraints. The purpose of this article is to guide every individual on how they can debug their code efficiently during a contest.

Prerequisite: Setting up Sublime Text for C++ Competitive Programming Environment

Time is something that is precious and it matters a lot during a coding contest. When writing a code, errors do come and programmers often tend to spend a lot of time debugging it.  Often programmers deal with complex data structures during a contest and it is required to debug them in the given time constraint. 

This article focuses on how to debug C++ source code efficiently in Sublime Text (IDE) during a contest and save time. First of all, it is required to set up the file structure of our Sublime Text. Below are the steps to set up the file structure of Sublime Text.  

Step 1: Open the Sublime Text and follow the below steps:

1. Create three files:

• file.cpp: The file to write the code.
• inputf.txt: The file where we will be giving the input.
• outputf.txt: The file where the output will be displayed.

2. Now, perform the following steps:

• Select View > Layout > Columns: 3. This will create three columns in the workspace. Move the three files into three columns.
• Select View > Groups > Max Columns : 2 : input.txt and output.txt will get stacked in a single column.

Your Sublime Text would look similar to this:

Sublime Text

Step 2: Create a local function outside the main function. It is used to take input from the input.txt file and display output in the output.txt file. Below is the C++ code snippet for the same.

C++

// Declare this function outside
// the main function
void local()
{
  // In case of online judges (like
  // codechef, codeforces etc) these
  // lines will be skipped. In other
  // words these lines would be executed
  // in Sublime Text only
  #ifndef ONLINE_JUDGE

  freopen("input.txt", "r", stdin);
  freopen("output.txt", "w", stdout);

  // ONLINE_JUDGE
  #endif
}

Step 3: Call from the main function: 

// Call from the main function
local();

By combining the above steps our complete program would be:

C++

// C++ program to implement
// the above approach
#include <bits/stdc++.h>
using namespace std;

// Local function
void local()
{
  #ifndef ONLINE_JUDGE
  freopen("input.txt",
          "r", stdin);
  freopen("output.txt",
          "w", stdout);

  // ONLINE_JUDGE
  #endif
}

// Driver code
int main()
{
  local();
  return 0;
}

Step 4: Now the IDE would look similar to this:

Sublime Text

Debugging using print function:

Create a print function in our program whenever we need to print a variable or any data structure like vector, set, map, etc. Below is the C++ program to implement the same approach:

C++

// C++ program to implement
// the above approach
#include <bits/stdc++.h>
using namespace std;

// Driver code
int main()
{
  // Initializing a vector
  vector<int> vect = {2, 4, 10,
                      12, 17};

  // First operation
  for (auto& x : vect)
  {
    if (x % 2 == 0)
      x += 10;
    else
      x -= 10;
  }

  // Second operation
  for (auto& x : vect)
    x += 2;

  // Third operation
  for (auto& x : vect)
    x += 20;
}

Suppose something went wrong in our logic due to which desired output is not obtained during a contest and hence to check the status of vector after the first operation, one can create a print function outside the main function which accepts a vector.

C++

// print function outside the
// main function
void print(vector<int>& vect)
{
  cout << "vect " << ' ';
  cout << '[' << ' ';

  // Print vector elements
  for (auto x : vect)
  {
    cout << x << ' ';
  }
  cout << ']';
}

Whenever there is a need to check the vector elements one can call the print() function by passing the vector as an argument to the print function.

// Calling print function from main

print(vect);

Below is the complete C++ program to illustrate how to implement the above concept:

C++

// C++ program to implement
// the above concept
#include <bits/stdc++.h>
using namespace std;

// Print function for debugging
void print(vector<int>& vect)
{
  cout << "vect " << ' ';
  cout << '[' << ' ';

  // Print vector elements
  for (auto x : vect)
  {
    cout << x << ' ';
  }
  cout << ']';
}

// Driver code
int main()
{
  // Initializing a vector
  vector<int> vect = {2, 4, 10,
                      12, 17};

  // First operation
  for (auto& x : vect)
  {
    if (x % 2 == 0)
      x += 10;
    else
      x -= 10;
  }

  // Printing vect elements after
  // applying first operation
  // Checking the status of vect as
  // a part of debugging
  print(vect);

  // Second operation
  for (auto& x : vect)
    x += 2;

  // Third operation
  for (auto& x : vect)
    x += 20;

  int finalAnswer = 0;
  for (auto x : vect)
    finalAnswer += x;

  // Print the final answer
  cout << "\nFinal Answer: " <<
            finalAnswer;
  return 0;
}

Output

vect  [ 12 14 20 22 7 ]
Final Answer: 185

Disadvantages of this method:

• For the same data structure but having different data types there is a need to create multiple print functions. For example, there is a vector of integer type and a vector of string type, then in order to print elements, it is required to create two print functions outside the main function. One print function will accept a vector of integer type and another print function will accept a vector of string type.
• Contents of the vector would be printed along with the desired values in the same output.txt file which might be confusing for us.
• There is a need to comment statements that are used to call a print function from the main function, before eventually submitting the source code file to the online judge (Codeforces, Spoj, Codechef, etc).

Debugging using template:

In the above method, the data type of vector is hardcoded. The template can be used in C++. A template is a simple and yet very powerful tool in C++. The simple idea is to pass data type as a parameter so that there is no need to write the same code (print function) for different data types. Below is the C++ code snippet for the template:

C++

// One print function works for
// all data types.  This would work
// even for user defined types if
// operator '>' is overloaded
template <typename T>

void print(vector<T> vect)
{
    // body
}

Below is the complete C++ program to illustrate the above concept:

C++

// C++ program to implement
// the above approach
#include <bits/stdc++.h>
using namespace std;

// Using template so that this
// function works for all data
// types
template <typename T> void print(
          vector<T>& vect)
{
  cout << "vect " << ' ';
  cout << '[' << ' ';

  for (auto x : vect)
  {
    cout << x << ' ';
  }
  cout << ']';
  cout << '\n';
}

// Driver code
int main()
{
  vector<int> vect1 = {2, 4, 10,
                       12, 17};

  for (auto& x : vect1)
  {
    if (x % 2 == 0)
      x += 10;
    else
      x -= 10;
  }

  // Printing vect1 elements
  print(vect1);

  // Initializing a vector of
  // string type
  vector<string> vect2 = {"Geeks",
                          "for", "Geeks"};

  // Printing vect2 elements
  print(vect2);

  // Modifying vect2
  // push back string "is great"
  vect2.push_back("is the great");

  // Printing vect2 after modification
  print(vect2);

  int finalAnswer = 0;
  for (auto x : vect1)
    finalAnswer += x;
  cout << "Final Answer: " <<
           finalAnswer;
  return 0;
}

Output

vect  [ 12 14 20 22 7 ]
vect  [ Geeks for Geeks ]
vect  [ Geeks for Geeks is the great ]
Final Answer: 75

A similar thing can be done with any data structure like a set, multiset, pairs, etc. Below is the implementation using the set:

C++

// C++ program to implement
// the above approach
#include <bits/stdc++.h>
using namespace std;

// Using template so that this
// function works for all data
// types
template <typename T> void print(
          set<T>& set1)
{
  cout << "set " << ' ';
  cout << '[' << ' ';

  for (auto x : set1)
  {
    cout << x << ' ';
  }
  cout << ']';
  cout << '\n';
}

// Driver code
int main()
{
  // Declaring a set
  set<int> set1;

  // Inserting elements in the set
  for (int i = 0; i < 10; i++)
    set1.insert(i);

  // Printing set1 elements
  print(set1);

  // Declaring another set of
  // string type
  set<string> set2;

  // Inserting elements in the set
  set2.insert("GeeksforGeeks");

  // Printing set2 elements
  print(set2);

  int finalAnswer = 0;

  for (auto x : set1)
    finalAnswer += x;
  cout << "Final Answer: " <<
           finalAnswer;
  return 0;
}

Output

set  [ 0 1 2 3 4 5 6 7 8 9 ]
set  [ GeeksforGeeks ]
Final Answer: 45

Disadvantages of this method:

• The above method is not very efficient as each time before submitting the program there is a need to comment print statements inside the main function.
• Elements of the data structure would be printed along with other desired values in the same output.txt file which might be confusing for us.

Debugging using cerr:

The idea is to use the combination of cerr (error stream) and file handling in the program. Create a separate file (error.txt) and use cerr stream instead of cout stream. Finally, with the help of file handling, print the status of data structure in the error.txt file.

Step 1: Firstly add the following snippets outside the main function:

• To print a variable we can create a print function with a template definition just above the function:

C++

//Template definition
template <typename T>

//Function to print the variable
void print(T x)
{
  // Using error stream to print
  // the variable
  cerr << x;
}

• To print vector elements we can create a print function with a template definition just above the function:

C++

// Template definition
template <typename T>

// Function to print the elements
// of the vector
void print(vector<T>& a)
{
  cerr << '[' << ' ';

  for (auto x : a)
  {
    // Same to print a variable (Function
    // Overloading)
    print(x);

    cerr << ' ';
  }
  cerr << ']';
}

• To print set elements arranged in non-descending order we can create a print function with a template definition just above the function:

C++

//Template definition
template <typename T>

// Function to print elements of the
// set arranged in non-descending order
void print(set<T>& a)
{
  cerr << '[' << ' ';

  for (auto x : a)
  {
    // Same as printing a variable
    // (Function Overloading)
    print(x);

    cerr << ' ';
  }
  cerr << ']';
}

• To print set elements arranged in non-ascending order we can create a print function with a template definition just above the function:

C++

template <typename T>

// Function to print the set elements
// arranged in non-ascending order
void print(set<T, greater<T> >& a)
{
  cerr << '[' << ' ';

  for (auto x : a)
  {
    // same as printing a variable
    // (Function Overloading)
    print(x);

    cerr << ' ';
  }
  cerr << ']';
}

• To print unordered set elements, we can create a print function with a template definition just above the function:

C++

// Template definition
template <typename T>

// Function to print unordered
// set elements
void print(unordered_set<T>& a)
{
  cerr << '[' << ' ';

  for (auto x : a)
  {
    // Same as printing a variable
    // Using the concept of function
    // overloading
    print(x);

    cerr << ' ';
  }
  cerr << ']';
}

• To print map elements, we can create a print function with a template definition just above the function:

C++

//Template definition
template <typename T, typename V>

//Function to print map elements
// arranged in non-descending order
void print(map<T, V>& a)
{
  cerr << "[ ";

  for (auto i : a)
  {
    // Same as variable using the
    // concept of function overloading
    print(i);

    cerr << " ";
  }
  cerr << "]";
}

• To print unordered map elements, we can create a print function with a template definition just above the function:

C++

//Template definition
template <typename T, typename V>

//Function to print unordered map elements
void print(unordered_map<T, V>& a)
{
  cerr << "[ ";
  for (auto i : a)
  {
    // Same as variable using the
    // concept of function overloading
    print(i);

    cerr << " ";
  }
  cerr << "]";
}

• To print multiset elements arranged in non-descending order, we can create a print function with a template definition just above the function:

C++

//Template definition
template <typename T>

//Function to print multiset elements
// arranged in non-descending order
void print(multiset<T>& a)
{
  cerr << '[' << ' ';

  for (auto x : a)
  {
    // Same as variable using the
    // concept of function overloading
    print(x);

    cerr << ' ';
  }
  cerr << ']';
}

• To print multiset elements, arranged in non-ascending order we can create a print function with a template definition just above the function:

C++

//Template definition
template <typename T>

//Function to print elements of a
// multiset arranged in non-ascending order
void print(multiset<T, greater<T> >& a)
{
  cerr << '[' << ' ';

  for (auto x : a)
  {
    // Same as variable using the
    // concept of function overloading
    print(x);

    cerr << ' ';
  }
  cerr << ']';
}

• To print unordered set elements, we can create a print function with a template definition just above the function:

C++

// Template definition
template <typename T>

// Print function to print unordered
// set elements
void print(unordered_set<T>& a)
{
  cerr << '[' << ' ';

  for (auto x : a)
  {
    // Same as variable using the
    // concept of function overloading
    print(x);

    cerr << ' ';
  }
  cerr << ']';
}

• To print vector of vectors elements, we can create a print function with a template definition just above the function:

C++

// Template definition
template <typename T>

// Function to print vector of
// vectors elements
void print(vector<vector<T> >& a)
{
  cerr << "[ ";

  for (auto i : a)
  {
    // Same as variable using the
    // concept of function overloading
    print(i);

    cerr << " ";
  }
  cerr << "]";
}

• To print a pair of elements, we can create a print function with a template definition just above the function:

C++

// Template definition
template <typename T, typename V>

// Function to print elements of a pair
void print(pair<T, V> x)
{
  // Same as printing the variable using
  // the concept of function overloading
  print(x.ff);

  cerr << ':';

  // Same as variable using the concept
  // of function overloading
  print(x.ss);
}

• To print a pair of vectors elements, we can create a print function with a template definition just above the function:

C++

// Template definition
template <typename T, typename V>

// Function to print vector of
// pairs elements
void print(vector<pair<T, V> >& a)
{
  cerr << '[' << ' ';

  for (auto x : a)
  {
    // Same as printing a variable using
    // the concept of function overloading
    print(x.ff);
    cerr << ":";

    // Same as printing a variable using
    // the concept of function overloading
    print(x.ss);
    cerr << ' ';
  }
  cerr << ']';
}

Step 2: Create one more new file (error.txt) and make sure it is in the same folder.

error.txt file: All the elements of the data structures that we have mentioned in the above snippets would be printed in this text file only without affecting the output.txt file.

Note that we want to write in this file using error stream (cerr). Again help from ifndef and endif preprocessor directives can be taken.

C++

// We want to skip writing on error.txt
// file when online judge (Codechef,
// Codeforces, etc) is defined
#ifndef ONLINE_JUDGE
    freopen("error.txt", "w", stderr);

// ONLINE_JUDGE
#endif

After adding the above lines in our local function, the complete function becomes:

C++

// Now local function would look like:
void local()
{
  #ifndef ONLINE_JUDGE
  freopen("input.txt", "r", stdin);
  freopen("output.txt", "w", stdout);

  // ONLINE_JUDGE
  #endif

  // It basically means that these
  // statements (Between ifndef and
  // endif) would be skipped / ignored
  // if ONLINE_JUDGE is defined We don't
  // need to comment "local();" statement
  // in our function while submitting our
  // source code file to online judges.
  // It would be handled automatically

  #ifndef ONLINE_JUDGE
  freopen("error.txt", "w", stderr);

  // ONLINE_JUDGE
  #endif
}

Step 3: Also, we don’t want to comment debug(data_structure) statements while submitting the source code file to online judges. In simple words, there is a need to figure out a way so that debug functions will work for the sublime text (IDE) but they would be skipped/ignored for online judges.
Again, this can be achieved by using ifndef and endif preprocessor directives again in the source code.

C++

// If online judge is defined
#ifndef ONLINE_JUDGE
#define debug(x)
cerr << #x << "  ";
print(x);
cerr << '\n';

// If Online Judge is not defined
#else
#define debug(x)
#endif

Now the IDE would look similar to this:

Step 4: Whenever there is a need to check the status of any data structure, the following call can be made:

// Calling from the main function
debug(dataStructure);

Step 5: Below is the implementation of the above method:

Example 1:

C++

/* It is recommended below snippets in
   your template file of competitive programming */
#include <bits/stdc++.h>
using namespace std;

// Debugging Functions

template<class T>void print(T x)
{
  cerr << x;
}
template<class T, class V>
         void print(pair<T , V> x)
{
  print(x.ff);
  cerr << ':';
  print(x.ss);
}
template<class T>
         void print(vector<T> &a)
{
  cerr << '[' << ' ';
  for(auto x : a)
  {
    print(x);
    cerr << ' ';
  }
  cerr << ']';
}
template<class T>
         void print(set<T> &a)
{
  cerr << '[' << ' ';
  for(auto x : a)
  {
    print(x);
    cerr << ' ';
  }
  cerr << ']';
}
template<class T>
         void print(set<T,
                    greater<T>> &a)
{
  cerr << '[' << ' ';
  for(auto x : a)
  {
    print(x);
    cerr << ' ';
  }
  cerr << ']';
}
template<class T>
         void print(multiset<T> &a)
{
  cerr << '[' << ' ';
  for(auto x : a)
  {
    print(x);
    cerr << ' ';
  }
  cerr << ']';
}
template<class T>
         void print(multiset<T,
                    greater<T>> &a)
{
  cerr << '[' << ' ';
  for(auto x : a)
  {
    print(x);
    cerr << ' ';
  }
  cerr << ']';
}
template<class T>
         void print(unordered_set<T> &a)
{
  cerr << '[' << ' ';
  for(auto x : a)
  {
    print(x);
    cerr << ' ';
  }
  cerr << ']';
}
template<class T, class V>
         void print(vector<pair<T, V>> &a)
{
  cerr << '[' << ' ';
  for(auto x : a)
  {
    print(x.ff);
    cerr << ":";
    print(x.ss);
    cerr << ' ';
  }
  cerr << ']';
}
template <class T, class V>
          void print(map <T, V> &a)
{
  cerr << "[ ";
  for (auto i : a)
  {
    print(i);
    cerr << " ";
  }
  cerr << "]";
}
template <class T, class V>
          void print(unordered_map <T, V> &a)
{
  cerr << "[ ";
  for (auto i : a)
  {
    print(i);
    cerr << " ";
  }
  cerr << "]";
}
template <class T>
          void print(vector<vector<T>> &a)
{
  cerr << "[ ";
  for (auto i : a)
  {
    print(i);
    cerr << " ";
  }
  cerr << "]";
}

void local()
{
  // ONLINE_JUDGE
  #ifndef ONLINE_JUDGE
  freopen("input.txt", "r", stdin);
  freopen("output.txt", "w", stdout);
  #endif

  // ONLINE_JUDGE
  #ifndef ONLINE_JUDGE
  freopen("error.txt", "w", stderr);
  #endif

  #ifndef ONLINE_JUDGE
  #define debug(x)
  cerr << #x << "  ";
  print(x);
  cerr << '\n';
  #else
  #define debug(x)
  #endif
}

// Driver code
int main()
{
  local();

  // Number of elements in the vector
  int n;

  // Taking input from the user
  // through input.txt file
  cin >> n;

  // Declaring a vector of integer
  // type of size n
  vector<int> vect1(n);

  // Initializing the vector
  for(int i = 0 ; i < n ; i++)
    cin >> vect1[i];

  // Modifying the vector
  for (auto& x : vect1)
  {
    if (x % 2 == 0)
      x += 10;
    else
      x -= 10;
  }

  // Printing vect1 elements
  // It will be printed in error.txt
  // file using cerr stream
  debug(vect1);

  // Initializing a vector of string type
  vector<string> vect2 = {"Geeks", "for", "Geeks"};

  // Printing vect2 elements
  // It will be printed in error.txt
  // file using cerr stream
  debug(vect2);

  // Modifying vect2
  // push back string "is great"
  vect2.push_back("is the great");

  // Printing vect2 after modification
  // It will be printed in error.txt
  // file using cerr stream
  debug(vect2);

  // Calculating the answer
  int finalAnswer = 0;
  for (auto x : vect1)
    finalAnswer += x;

  // Finally, printing answer in output.txt
  // file using cout stream
  cout << "Final Answer: " << finalAnswer;

  return 0;
}

file.cpp file:

input.txt file

output.txt file

error.txt file

Example 2:

C++

/* It is recommended below snippets in
   your template file of competitive programming */

#include <bits/stdc++.h>
using namespace std;

// Debugging Functions
template<class T>void print(T x)
{
  cerr << x;
}
template<class T , class V>
         void print(pair<T, V> x)
{
  print(x.ff);
  cerr << ':';
  print(x.ss);
}
template<class T>
         void print(vector<T> &a)
{
  cerr << '[' << ' ';
  for(auto x : a)
  {
    print(x);
    cerr << ' ';
  }
  cerr << ']';
}
template<class T>
         void print(set<T> &a)
{
  cerr << '[' << ' ';
  for(auto x : a)
  {
    print(x);
    cerr << ' ';
  }
  cerr << ']';
}
template<class T>
         void print(set<T,
                    greater<T>> &a)
{
  cerr << '[' << ' ';
  for(auto x : a)
  {
    print(x);
    cerr << ' ';
  }
  cerr << ']';
}
template<class T>
         void print(multiset<T> &a)
{
  cerr << '[' << ' ';
  for(auto x : a)
  {
    print(x);
    cerr << ' ';
  }
  cerr << ']';
}
template<class T>
         void print(multiset<T,
                    greater<T>> &a)
{
  cerr << '[' << ' ';
  for(auto x : a)
  {
    print(x);
    cerr << ' ';
  }
  cerr << ']';
}
template<class T>
         void print(unordered_set<T> &a)
{
  cerr << '[' << ' ';
  for(auto x : a)
  {
    print(x);
    cerr << ' ';
  }
  cerr << ']';
}
template<class T, class V>
         void print(vector<pair<T, V>> &a)
{
  cerr << '[' << ' ';
  for(auto x : a)
  {
    print(x.ff);
    cerr << ":";
    print(x.ss);
    cerr << ' ';
  }
  cerr << ']';
}
template <class T, class V>
          void print(map <T, V> &a)
{
  cerr << "[ ";
  for (auto i : a)
  {
    print(i);
    cerr << " ";
  }
  cerr << "]";
}
template <class T, class V>
          void print(unordered_map <T, V> &a)
{
  cerr << "[ ";
  for (auto i : a)
  {
    print(i);
    cerr << " ";
  }
  cerr << "]";
}
template <class T>
          void print(vector<vector<T>> &a)
{
  cerr << "[ ";
  for (auto i : a)
  {
    print(i);
    cerr << " ";
  }
  cerr << "]";
}

void local()
{
  // ONLINE_JUDGE
  #ifndef ONLINE_JUDGE
  freopen("input.txt", "r", stdin);
  freopen("output.txt", "w", stdout);
  #endif

  // ONLINE_JUDGE
  #ifndef ONLINE_JUDGE
  freopen("error.txt", "w", stderr);
  #endif

  #ifndef ONLINE_JUDGE
  #define debug(x)
  cerr << #x << "  ";
  print(x);
  cerr << '\n';
  #else
  #define debug(x)
  #endif
}

// Driver code
int main()
{
  local();

  // Number of elements in the set
  int n;

  // Taking input from the user
  // through input.txt file
  cin >> n;

  // Declaring a set of integers
  set<int> set1;

  for(int i = 0 ; i < n ; i++)
  {
    int number;

    // Taking input from the user
    // through input.txt file
    cin >> number;

    //Inserting in the set
    set1.insert(number);
  }


  // Erasing from the set
  if(!set1.empty())
  {
    // erasing the first element
    // of the set
    set1.erase(set1.begin());
  }

  // Printing set1 elements
  // It will be printed in error.txt
  // file using cerr stream
  debug(set1);

  // Declaring another set
  set<string> set2;

  // Inserting in the set
  set2.insert("GeeksforGeeks");

  // Printing set2 elements
  // It will be printed in error.txt file
  // using cerr stream
  debug(set2);

  // Inserting in set
  // Insert the string "is great"
  set2.insert("Geek");

  // Printing set2 elements after
  // inserting into the set, It will
  // be printed in error.txt file
  // using cerr stream
  debug(set2);

  // Calculating the answer
  int finalAnswer = 0;
  for (auto x : set1)
    finalAnswer += x;

  // Finally, printing answer in output.txt
  // file using cout stream
  cout << "Final Answer: " << finalAnswer;

  return 0;
}

file.cpp file:

input.txt file

output.txt file

error.txt file

Advantage of this method of debugging:

• Now there is no need to comment on each of the debug statements in the program before submitting the source code file to online judges.
• The data structure or STL elements would be printed in a separate file (error.txt) and desired output values would be printed in the output.txt file, making it more readable.
• In a nutshell, this can save a lot of time during a coding contest.