Don't treat c++ "cerr(stderr)" as a RUNTIME ERROR about autocp HOT 2 CLOSED

Hi mym0404, I had no idea that online judges ignore stderr if stdout is right. The current implementation of the local judge ignores stdout if there is anything in stderr. Thanks for bringing it up, love to solve it.

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Yes many online judges treats stderr as a error. So programmers remove debugging line before their submission.
But using stderr as useful for debugging in local environment.
For example, this is my template.

#ifdef LOCAL
template<size_t S>
string to_string(const bitset<S> &x) { return x.to_string(); }
string to_string(const string &x) { return '"' + x + '"'; }
string to_string(char x) { return string{'\'', x, '\''}; }
string to_string(bool x) { return x ? "true" : "false"; }
template<class H, class T>
string to_string(const pair<H, T> &x) { return "(" + to_string(x.fi) + ", " + to_string(x.se) + ")"; }
template<class T>
string to_string(T x) {
   string ret = "[";
   for (const auto &i: x) ret += to_string(i) + ", ";
   if (sz(ret) > 1) ret = ret.substr(0, sz(ret) - 2);
   return ret += "]";
}
string to_string(const char *x) { return {x}; }
string to_string() { return ""; }
template<class H, class... T>
string to_string(H h, T... t) { return to_string(h) + ", " + to_string(t...); }
#define debug(...) sizeof( (char[]){#__VA_ARGS__} ) == 1 ? cerr << endl \
: cerr << "[" << #__VA_ARGS__ << "]: " << to_string(__VA_ARGS__) << endl
#else
#define debug(...) 1
#endif

If I define LOCAL only my local machine, then OJ compiler doesn't matter.
It prints debugging line in only my local machine like the following.

Also I can submit this code without removing debug(1). Because OJ doesn't define LOCAL macro.

AutoCP is local testing tool and seems to this behavior is incompatible in some case like me.

It will be wonderful if I can use stderr for AutoCP also.

But it is your choice. Because I can configure AutoCP build command like without LOCAL macro and it doesn't need delete code manually for AutoCP testing.

I just suggest this 😀

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