GCC 5.1 is too old and slow for today standard! I have encountered so many problem because of it

"qsort" implementation is slow:

• • comment: https://mirror.codeforces.com/blog/entry/150510#comment-1342922
• • code 2193D: (359841071 TLE) (360069514 Fixed by modifying sort function)
• • code 2193F (360069301 TLE) (360069436 Fixed by modifying sort function)

"%lf" on printf is not working (scanf is worked), should be "%f" but that for float not double:

• • code 500D: (364906153 WA) (364906215 AC after 10 retries figuring out that the problem was %lf!)
• • comment: you can see on my WA submission that I just printing 2.0 but output always 0.0 for unknown reason :(

sscanf / sprintf is slow:

• • comment: https://mirror.codeforces.com/blog/entry/152085#comment-1353829
• • code 2204E: (367013757 TLE using sscanf/sprintf) (367016186 AC using manual number -> string -> number conversion)

"%hhu" is not working (can't scan / print unsigned char number from stdin / to stdout directly):

• • code 2208C: (366675178 WA when using uint8) (366676632 AC after using double)
• • comment: compiler is too old for the %hhu feature :(

Calling printf frequently is slow in C but fast on C++:

• • Comment from @Benq: https://mirror.codeforces.com/blog/entry/152448?#comment-1356227
• • Code 2211B: (368619996 C 1500ms) (368619986 C++ 78ms) <-- both of this has the exact same code, thanks @Benq for testing this <3
• • Comment from me: https://mirror.codeforces.com/blog/entry/152448?#comment-1356222
• • Code 2211B: (368617316 Fast algo, a lot of printf: TLE) (368617206 Slow algo, buffer the output to string first: AC 125ms)

Conclusion: The old compiler has a lot of problem! Imagine using unoptimized gcc 5 on 2026 >,< Now there is gcc 15 which is 10 versions above. Why not upgrade the compiler? @MikeMirzayanov