I've bumped into [this blog post](https://codeforces.me/blog/entry/95572) by [user:imtiyazrasool92,2021-10-03] (unfortunately, it's already deleted). They've found out that simply declaring a global variable called `read` makes your program behave strangely on Codeforces: the outcome of [submission:130645378] is `RUNTIME_ERROR`, `Exit code is 2147483647`, and here is the code:↵
↵
~~~~~↵
#include <iostream>↵
int read;↵
int main(){↵
std::ios_base::sync_with_stdio(false);↵
std::cin >> read;↵
}↵
~~~~~↵
↵
I was unable to minimize the example any further.↵
↵
The original post was even more interesting: [submission:130642683] is Accepted, but [submission:130643108] is Runtime Error all of a sudden.↵
↵
The compiler on Codeforces is `G++17 9.2.0 (64 bit, msys2)`. However, I was able to reproduce the issue both on my local machine (`g++ (Rev2, Built by MSYS2 project) 10.3.0`) and the latest GCC on [Godbolt](https://godbolt.org/z/PreqhjfGb) as long as the `-static` key is used for compilation [just like on Codeforces](https://codeforces.me/blog/entry/75004?locale=ru). Clang is also affected.↵
↵
It looks like the `read` variable here replaces the standard Linux `read` function (which is emulated by msys2). Here is a symmetrical example:↵
↵
~~~~~↵
#include <iostream>↵
int write;↵
int main(){↵
std::ios_base::sync_with_stdio(false);↵
std::cout << 10;↵
}↵
~~~~~↵
↵
And here is one more ([submission:130646314]), although now I at least get some warnings:↵
↵
~~~~~↵
int malloc;↵
int main(){↵
}↵
~~~~~↵
↵
~~~~~↵
a.cpp:1:5: warning: built-in function 'malloc' declared as non-function [-Wbuiltin-declaration-mismatch]↵
1 | int malloc;↵
| ^~~~~~↵
↵
~~~~~↵
↵
My understanding is that all these examples invoke [ODR violation](https://en.wikipedia.org/wiki/One_Definition_Rule), which makes the program ill-formed (invalid) without any requirements on the compiler to emit the error. However, I am not sure, so I [asked on StackOverflow](https://stackoverflow.com/questions/69424363/is-it-allowed-to-name-a-global-variable-read-or-malloc-in-c).↵
↵
Any other ideas?
↵
~~~~~↵
#include <iostream>↵
int read;↵
int main(){↵
std::ios_base::sync_with_stdio(false);↵
std::cin >> read;↵
}↵
~~~~~↵
↵
I was unable to minimize the example any further.↵
↵
The original post was even more interesting: [submission:130642683] is Accepted, but [submission:130643108] is Runtime Error all of a sudden.↵
↵
The compiler on Codeforces is `G++17 9.2.0 (64 bit, msys2)`. However, I was able to reproduce the issue both on my local machine (`g++ (Rev2, Built by MSYS2 project) 10.3.0`) and the latest GCC on [Godbolt](https://godbolt.org/z/PreqhjfGb) as long as the `-static` key is used for compilation [just like on Codeforces](https://codeforces.me/blog/entry/75004?locale=ru). Clang is also affected.↵
↵
It looks like the `read` variable here replaces the standard Linux `read` function (which is emulated by msys2). Here is a symmetrical example:↵
↵
~~~~~↵
#include <iostream>↵
int write;↵
int main(){↵
std::ios_base::sync_with_stdio(false);↵
std::cout << 10;↵
}↵
~~~~~↵
↵
And here is one more ([submission:130646314]), although now I at least get some warnings:↵
↵
~~~~~↵
int malloc;↵
int main(){↵
}↵
~~~~~↵
↵
~~~~~↵
a.cpp:1:5: warning: built-in function 'malloc' declared as non-function [-Wbuiltin-declaration-mismatch]↵
1 | int malloc;↵
| ^~~~~~↵
↵
~~~~~↵
↵
My understanding is that all these examples invoke [ODR violation](https://en.wikipedia.org/wiki/One_Definition_Rule), which makes the program ill-formed (invalid) without any requirements on the compiler to emit the error. However, I am not sure, so I [asked on StackOverflow](https://stackoverflow.com/questions/69424363/is-it-allowed-to-name-a-global-variable-read-or-malloc-in-c).↵
↵
Any other ideas?
