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C++ Debug Template 🛠

Simplify variable tracking across functions and loops!

Note: For latest updates and a colored stderr version of this template, visit my Github.

Longer Template (std >= C++11)

#ifndef DEBUG_TEMPLATE_CPP
#define DEBUG_TEMPLATE_CPP
#include <bits/stdc++.h>
// #define cerr cout
namespace __DEBUG_UTIL__
{
    using namespace std;
    /* Primitive Datatypes Print */
    void print(const char *x) { cerr << x; }
    void print(bool x) { cerr << (x ? "T" : "F"); }
    void print(char x) { cerr << '\'' << x << '\''; }
    void print(signed short int x) { cerr << x; }
    void print(unsigned short int x) { cerr << x; }
    void print(signed int x) { cerr << x; }
    void print(unsigned int x) { cerr << x; }
    void print(signed long int x) { cerr << x; }
    void print(unsigned long int x) { cerr << x; }
    void print(signed long long int x) { cerr << x; }
    void print(unsigned long long int x) { cerr << x; }
    void print(float x) { cerr << x; }
    void print(double x) { cerr << x; }
    void print(long double x) { cerr << x; }
    void print(string x) { cerr << '\"' << x << '\"'; }
    template <size_t N>
    void print(bitset<N> x) { cerr << x; }
    void print(vector<bool> v)
    { /* Overloaded this because stl optimizes vector<bool> by using
          _Bit_reference instead of bool to conserve space. */
        int f = 0;
        cerr << '{';
        for (auto &&i : v)
            cerr << (f++ ? "," : "") << (i ? "T" : "F");
        cerr << "}";
    }
    /* Templates Declarations to support nested datatypes */
    template <typename T>
    void print(T &&x);
    template <typename T>
    void print(vector<vector<T>> mat);
    template <typename T, size_t N, size_t M>
    void print(T (&mat)[N][M]);
    template <typename F, typename S>
    void print(pair<F, S> x);
    template <typename T, size_t N>
    struct Tuple;
    template <typename T>
    struct Tuple<T, 1>;
    template <typename... Args>
    void print(tuple<Args...> t);
    template <typename... T>
    void print(priority_queue<T...> pq);
    template <typename T>
    void print(stack<T> st);
    template <typename T>
    void print(queue<T> q);
    /* Template Datatypes Definitions */
    template <typename T>
    void print(T &&x)
    {
        /*  This works for every container that supports range-based loop
            i.e. vector, set, map, oset, omap, dequeue */
        int f = 0;
        cerr << '{';
        for (auto &&i : x)
            cerr << (f++ ? "," : ""), print(i);
        cerr << "}";
    }
    template <typename T>
    void print(vector<vector<T>> mat)
    {
        int f = 0;
        cerr << "\n~~~~~\n";
        for (auto &&i : mat)
        {
            cerr << setw(2) << left << f++, print(i), cerr << "\n";
        }
        cerr << "~~~~~\n";
    }
    template <typename T, size_t N, size_t M>
    void print(T (&mat)[N][M])
    {
        int f = 0;
        cerr << "\n~~~~~\n";
        for (auto &&i : mat)
        {
            cerr << setw(2) << left << f++, print(i), cerr << "\n";
        }
        cerr << "~~~~~\n";
    }
    template <typename F, typename S>
    void print(pair<F, S> x)
    {
        cerr << '(';
        print(x.first);
        cerr << ',';
        print(x.second);
        cerr << ')';
    }
    template <typename T, size_t N>
    struct Tuple
    {
        static void printTuple(T t)
        {
            Tuple<T, N - 1>::printTuple(t);
            cerr << ",", print(get<N - 1>(t));
        }
    };
    template <typename T>
    struct Tuple<T, 1>
    {
        static void printTuple(T t) { print(get<0>(t)); }
    };
    template <typename... Args>
    void print(tuple<Args...> t)
    {
        cerr << "(";
        Tuple<decltype(t), sizeof...(Args)>::printTuple(t);
        cerr << ")";
    }
    template <typename... T>
    void print(priority_queue<T...> pq)
    {
        int f = 0;
        cerr << '{';
        while (!pq.empty())
            cerr << (f++ ? "," : ""), print(pq.top()), pq.pop();
        cerr << "}";
    }
    template <typename T>
    void print(stack<T> st)
    {
        int f = 0;
        cerr << '{';
        while (!st.empty())
            cerr << (f++ ? "," : ""), print(st.top()), st.pop();
        cerr << "}";
    }
    template <typename T>
    void print(queue<T> q)
    {
        int f = 0;
        cerr << '{';
        while (!q.empty())
            cerr << (f++ ? "," : ""), print(q.front()), q.pop();
        cerr << "}";
    }
    /* Printer functions */
    void printer(const char *) {} /* Base Recursive */
    template <typename T, typename... V>
    void printer(const char *names, T &&head, V &&...tail)
    {
        /* Using && to capture both lvalues and rvalues */
        int i = 0;
        for (size_t bracket = 0; names[i] != '\0' and (names[i] != ',' or bracket != 0); i++)
            if (names[i] == '(' or names[i] == '<' or names[i] == '{')
                bracket++;
            else if (names[i] == ')' or names[i] == '>' or names[i] == '}')
                bracket--;
        cerr.write(names, i) << " = ";
        print(head);
        if (sizeof...(tail))
            cerr << " ||", printer(names + i + 1, tail...);
        else
            cerr << "]\n";
    }
    /* PrinterArr */
    void printerArr(const char *) {} /* Base Recursive */
    template <typename T, typename... V>
    void printerArr(const char *names, T arr[], size_t N, V... tail)
    {
        size_t ind = 0;
        for (; names[ind] and names[ind] != ','; ind++)
            cerr << names[ind];
        for (ind++; names[ind] and names[ind] != ','; ind++)
            ;
        cerr << " = {";
        for (size_t i = 0; i < N; i++)
            cerr << (i ? "," : ""), print(arr[i]);
        cerr << "}";
        if (sizeof...(tail))
            cerr << " ||", printerArr(names + ind + 1, tail...);
        else
            cerr << "]\n";
    }
}
#ifndef ONLINE_JUDGE
#define debug(...) std::cerr << __LINE__ << ": [", __DEBUG_UTIL__::printer(#__VA_ARGS__, __VA_ARGS__)
#define debugArr(...) std::cerr << __LINE__ << ": [", __DEBUG_UTIL__::printerArr(#__VA_ARGS__, __VA_ARGS__)
#else
#define debug(...)
#define debugArr(...)
#endif
#endif

Shorter Template, (std >= C++20) (Recommended)

#ifndef DEBUG_TEMPLATE_CPP
#define DEBUG_TEMPLATE_CPP
#include <bits/stdc++.h>
// #define cerr cout
namespace __DEBUG_UTIL__
{
    using namespace std;
    template <typename T>
    concept is_iterable = requires(T &&x) { begin(x); } &&
                          !is_same_v<remove_cvref_t<T>, string>;
    void print(const char *x) { cerr << x; }
    void print(char x) { cerr << "\'" << x << "\'"; }
    void print(bool x) { cerr << (x ? "T" : "F"); }
    void print(string x) { cerr << "\"" << x << "\""; }
    void print(vector<bool> &v)
    { /* Overloaded this because stl optimizes vector<bool> by using
         _Bit_reference instead of bool to conserve space. */
        int f = 0;
        cerr << '{';
        for (auto &&i : v)
            cerr << (f++ ? "," : "") << (i ? "T" : "F");
        cerr << "}";
    }
    template <typename T>
    void print(T &&x)
    {
        if constexpr (is_iterable<T>)
            if (size(x) && is_iterable<decltype(*(begin(x)))>)
            { /* Iterable inside Iterable */
                int f = 0;
                cerr << "\n~~~~~\n";
                for (auto &&i : x)
                {
                    cerr << setw(2) << left << f++, print(i), cerr << "\n";
                }
                cerr << "~~~~~\n";
            }
            else
            { /* Normal Iterable */
                int f = 0;
                cerr << "{";
                for (auto &&i : x)
                    cerr << (f++ ? "," : ""), print(i);
                cerr << "}";
            }
        else if constexpr (requires { x.pop(); }) /* Stacks, Priority Queues, Queues */
        {
            auto temp = x;
            int f = 0;
            cerr << "{";
            if constexpr (requires { x.top(); })
                while (!temp.empty())
                    cerr << (f++ ? "," : ""), print(temp.top()), temp.pop();
            else
                while (!temp.empty())
                    cerr << (f++ ? "," : ""), print(temp.front()), temp.pop();
            cerr << "}";
        }
        else if constexpr (requires { x.first; x.second; }) /* Pair */
        {
            cerr << '(', print(x.first), cerr << ',', print(x.second), cerr << ')';
        }
        else if constexpr (requires { get<0>(x); }) /* Tuple */
        {
            int f = 0;
            cerr << '(', apply([&f](auto... args)
                               { ((cerr << (f++ ? "," : ""), print(args)), ...); },
                               x);
            cerr << ')';
        }
        else
            cerr << x;
    }
    template <typename T, typename... V>
    void printer(const char *names, T &&head, V &&...tail)
    {
        int i = 0;
        for (size_t bracket = 0; names[i] != '\0' and (names[i] != ',' or bracket != 0); i++)
            if (names[i] == '(' or names[i] == '<' or names[i] == '{')
                bracket++;
            else if (names[i] == ')' or names[i] == '>' or names[i] == '}')
                bracket--;
        cerr.write(names, i) << " = ";
        print(head);
        if constexpr (sizeof...(tail))
            cerr << " ||", printer(names + i + 1, tail...);
        else
            cerr << "]\n";
    }
    template <typename T, typename... V>
    void printerArr(const char *names, T arr[], size_t N, V... tail)
    {
        size_t i = 0;
        for (; names[i] and names[i] != ','; i++)
            cerr << names[i];
        for (i++; names[i] and names[i] != ','; i++)
            ;
        cerr << " = {";
        for (size_t ind = 0; ind < N; ind++)
            cerr << (ind ? "," : ""), print(arr[ind]);
        cerr << "}";
        if constexpr (sizeof...(tail))
            cerr << " ||", printerArr(names + i + 1, tail...);
        else
            cerr << "]\n";
    }

}
#ifndef ONLINE_JUDGE
#define debug(...) std::cerr << __LINE__ << ": [", __DEBUG_UTIL__::printer(#__VA_ARGS__, __VA_ARGS__)
#define debugArr(...) std::cerr << __LINE__ << ": [", __DEBUG_UTIL__::printerArr(#__VA_ARGS__, __VA_ARGS__)
#else
#define debug(...)
#define debugArr(...)
#endif
#endif

As of now both perform equally well, but my choice? C++20.

Simple Usage

int mat[3][5]{};
vector<int> v;
for (int i = 1; i <= 3; i++)
{
    v.push_back(i * i);
    debug(i, v);
}
debug(mat);

// stderr
23: [i = 1 || v = {1}]
23: [i = 2 || v = {1,4}]
23: [i = 3 || v = {1,4,9}]
25: [mat = 
~~~~~
0 {0,0,0,0,0}
1 {0,0,0,0,0}
2 {0,0,0,0,0}
~~~~~
]

This template supports datatypes such as:

🔢 Primitive: int, char, bool, long long int etc.

📚 STL: pair, tuple, vector, set, oset, map, omap, stack, queue, priority_queue, bitset etc.

📦 Arrays of all datatypes: int arr[], bool arr[], vector<int> adj[] etc.

🧩 Matrix: int dp[100][200], vector<vector<bool>> vis(100, vector<bool> (200, 0)) etc.

🕗 Arrays that have been decayed or declared at runtime like int arr[n].

📝 Rvalue Literals like "Hello", false, 'z', isSafe(i, j), dfs(u).

🧱 User defined structs / classes like Point, Node.

🤯 Even nested datatypes like map<string, vector<pair<char, unordered_set<long long>>>> WHATTT;.

Colored Template Preview

How to use it?

Let's say you have different datatypes such as:

Example

char Char = 'A';
int arr[] = {1, 2, 3, 4};
bitset<8> Bitset(100);
map<string, int> map_String_Int = {{"apple", 5}, {"banana", 3}, {"orange", 7}};

You can debug them like this debug(var1, var2, var3, var4, ...);

Example

debug(Char, arr, Bitset, map_String_Int);

// Output
21: [Char = 'A' || arr = {1,2,3,4} || Bitset = 01100100 || map_String_Int = {("apple",5),("banana",3),("orange",7)}]

If you have user defined structs / classes, you just need to make a print() function, and use debug(...) like you do :)

User-Defined struct/class printing.

struct Point
{
    int x{};
    int y{};
};
void print(Point ob)
{
    cerr << "(" << ob.x << "," << ob.y << ")";
}

In instances where array have decayed into pointer, or you declared array at runtime, use debugArr(arr, n);

What is Array Decay?

Note:

You don't need to remove debug(...) statements in your code when submitting it.
On platforms like Codeforces, there's a macro called ONLINE_JUDGE that's defined, automatically disregarding all your debug statements. This ensures your solution will be accepted unless there's a logical error.

How to Setup?

Copy this template into your own templates. The output will be directed to the stderr stream.
Alternatively you can make a separate header file and include this into your template

    #ifndef ONLINE_JUDGE
    #include "template.cpp"
    #else
    #define debug(...)
    #define debugArr(...)
    #endif

When using it for LeetCode uncomment #define cerr cout and before submitting change #ifndef to #ifdef to ignore debug(...);. For convenience, after changing it, copy it, and keep it pinned in your clipboard for repetitive use.

For Complete Beginners who need step by step tutorial (for VS Code), follow these steps:

Steps

If you liked this blog, please upvote it, I'd be really grateful :)

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Anshul_Johri's blog

C++ Debug Template 🛠

How to use it?

How to Setup?