diff --git a/src/others/cpp_tips.md b/src/others/cpp_tips.md new file mode 100644 index 000000000..85cdbf7f0 --- /dev/null +++ b/src/others/cpp_tips.md @@ -0,0 +1,27 @@ +--- +tags: + - Original +--- + +# C++ Tips and Tricks for Competition Programming + +## Faster I/O + +- `std::ios_base::sync_with_stdio(false)`: by default, C++ works with C++ iostreams (like `std::cin`, may not apply to new C++23 `std::print`/`std::println`) and C style stdio streams (like `stdin`) by synchronizing them. +Since you should never need C style I/O (like `scanf`, `printf`), in C++, disabling this synchronization will make C++ I/O competitive with C style `scanf`. +- `std::cin.tie(0)`: By default, iostreams flush cout every time you read from cin, so that you will always display any output before reading any input. +You can disable this automatic flushing to make I/O faster. The exception is for interactive problems with interleaved inputs and outputs, for which you can either not use `cin.tie(0)` or flush explicitly with `cout.flush()`/`cout.endl`. + +References: +[Dr. Dobbs - The Standard Librarian: IOStreams and Stdio](https://www.drdobbs.com/the-standard-librarian-iostreams-and-std/184401305), +[Codeforces - Best form of C++ I/O?](https://codeforces.com/blog/entry/6251) + +## Less Typing + +- `using namespace std;`: this saves lots of tedious typing of `std::` before all the standard library functions and objects. However, a blanket namespace import like this can cause name clashes, so don't name your variables or functions something common like `find` or anything from [this list](https://en.cppreference.com/w/cpp/symbol_index). +- `#include `: this is a catch-all implementation-defined header in g++ that avoids having a list of dozens of includes like `#include `, `#include `, `#include `, etc. It should work on any CP judge site, but it is not a standard header. On your local machine, it can be pre-compiled to greatly save compilation time. +- `#define int long long`: some people define `int` to always be (at least) 64-bit to avoid overflow issues, since most CP problems use numbers that fit in a 64-bit integer. However, this is **not recommended** because of many unexpected issues: + - C++ requires `main` to be a function returning `int` and not `long long`, so use `signed main` as a workaround. + - Function calls like `min(x, 0)` may complain that `0` is type `int`. + - Requires twice as much memory than `int` and may make the program slower, which may be important in extremely time-critical code. + - Otherwise you can use `typedef long long ll` or use the appropriate fixed-width integer types like `int64_t`. pFad - Phonifier reborn

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