fast input

general
,
1

can anyone suggest which is the fastest way of inputting in c++.

2

getchar_unlocked is very fast and easy to code ( nearly the fastest ), you can check its performance on INTEST question. Using it, you can make custom reading functions for strings, integers and basically everything. Like for inputting non-negative integers you can do:

#define gc getchar_unlocked
int read_int() {
  char c = gc();
  while(c<'0' || c>'9') c = gc();
  int ret = 0;
  while(c>='0' && c<='9') {
    ret = 10 * ret + c - 48;
    c = gc();
  }
  return ret;
}

On windows while testing , you can change #define gc getchar_unlocked to #define gc getchar and change back while submitting.

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3

There is no any special library in C/C++ for FASTIO.
The Fastest Method to print output in C/C++ is fwrite or fwrite_unlocked in stdio.h library.
Also there isn’t any special/Direct function to print output at once .

Indirectly,it can be achieved using append function ( appending all output strings to one single string and printing the final string)in cplusplus and even strcat function in string.h lib,but performance wise ,“Appending or concat + printing”,is slower ,even far slower than printf.

So the fastest way in c/c++ is :directly read the stream in the raw form, and extract the information required.Also put the output in raw form in a huge buffer and display it finally using fwrite.

Please go through the link

4

@amitsaharana: There is a better way to change code between local testing and online submission-

#ifndef ONLINE_JUDGE
    #define gc getchar
#else
    #define gc getchar_unlocked
#endif

This works because ONLINE_JUDGE is a macro which is defined on judge, and not defined on your local machine.
This is extremely useful, as you don’t have to change code before submitting.

1 Like
5

why in windows we can’t use getchar_unlocked()