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unalive's blog

[Help] debug template for ICPC
By unalive, 2 weeks ago, In English

I am unfortunately not very good at writing code and can barely function without an easy way to debug said code. I therefore need a debug template at ICPC and spent some time reducing the length of the debug template I use normally. I think it's pretty short already, but it seems like it can be shortened further. I don't know how to do so, hence this blog.

Some considerations:

  1. Can only use features introduced in C++ 17 or earlier, as my region is weird.
  2. Need to be able to debug all STL containers, and any nested versions thereof.

Now, if C++ 20 were allowed, one could simply use the following:

Code

__print() works by repeatedly considering the elements that constitute x and calling __print() on them (whilst ensuring that the output of each __print() call is separated by ,) until << is defined for x by default.

Now, what's the problem with making this code compatible with C++17?

The problem is that there doesn't seem to be a short (in terms of code length) way in C++17 to differentiate between pairs and iterable containers.

I found two solutions, both of which aren't good at all:

1) Use is_literal_type_v to check if T is a pair
Code

This will work if we have pairs like std::pair<int, float> but not with something like std::pair<int, vector<int>>. This is a significant loss of functionality since we now cannot debug things like map<int, vector<int>> which are often used.

2) Just create a separate templated function for pairs
Code

This is also bad because:

  1. Much longer code.
  2. Notice that we now need to use a class/struct/namespace for the two __print() functions as they can call each other.

Can someone help me fix these issues and/or make the code shorter in general? Right now, I think the last one is the best. I can't believe I spent the last 3 hours shortening a piece of code by 5 lines.

For whatever reason, GPT and Claude seems to be unhelpful here. I ran out of access to 4o trying to get it to help me, despite purchasing GPT plus T_T

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2 weeks ago, # |
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I just realized it cannot debug bitset either QAQ

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2 weeks ago, # |
  Vote: I like it -8 Vote: I do not like it 

string to_string(string s) {
  return '"' + s + '"';
}
string to_string(const char* s) {
  return to_string((string) s);
}
string to_string(bool b) {
  return (b ? "true" : "false");
}
template <typename A, typename B>
string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}
template <typename A>
string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto &x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}";
  return res;
}
void debug_out() { cerr << endl; }
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}
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    2 weeks ago, # ^ |
      Vote: I like it +8 Vote: I do not like it
    1. longer
    2. doesn't print argument list
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      2 weeks ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      what do you mean by argument list

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        2 weeks ago, # ^ |
        ← Rev. 2   Vote: I like it 0 Vote: I do not like it

        If you call debug(a, b, c), the template in the blog will output [a, b, c ] = [1, 2, 3]. Your code will just output 1 2 3.

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          2 weeks ago, # ^ |
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          not really because i use this #define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)

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    2 weeks ago, # ^ |
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    This also wouldn't work for pair<int, vector<int>>, since there is no declaration for cross-reference

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2 weeks ago, # |
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unalive orz

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2 weeks ago, # |
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Would something like this work? https://godbolt.org/z/fKMjoPhz8

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    2 weeks ago, # ^ |
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    I don't think this is a solution to the given problem
    It uses the requires keyword, which was introduced in C++20

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