using putchar_unlocked for fast output

Question

I wish to use fast input and output in my code. I understood the use of getchar_unlocked for fast input using the below function.

inline int next_int() {
    int n = 0;
    char c = getchar_unlocked();
    while (!('0' <= c && c <= '9')) {
        c = getchar_unlocked();
    }
    while ('0' <= c && c <= '9') {
        n = n * 10 + c - '0';
        c = getchar_unlocked();
    }
    return n;
}

can someone please explain me how to use fast output using putchar_unlocked() function?

I was going through this question and there someone said putchar_unlocked() could be used for fast output.

@aaronman i understand the problem i might face but i need to use it to decrease my time in codes i am practising — Tilak Raj Singh, Aug 02 '13 at 00:21
Why do you think your code needs to run faster, if you are using c++ you should use the c++ facilities for I/O — aaronman, Aug 02 '13 at 00:26
thats because cin and cout are even slower than scanf printf and getchar_unlocked and putchar_unlocked are fastest for input/output...what i need to do is just run my code fast...if its c or c++ doesnt matter to me...thats why i required it..currently the code i have written is in c++ if need be i could chnge it to c — Tilak Raj Singh, Aug 02 '13 at 00:31
let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/34661/discussion-between-aaronman-and-tilak-raj-singh) — aaronman, Aug 02 '13 at 00:31

score 9 · Answer 1 · edited Jul 31 '22 at 18:16

9

Well the following code works well for fast output using putchar_unlocked().

    #define pc(x) putchar_unlocked(x);
    inline void writeInt (int n)
    {
        int N = n, rev, count = 0;
        rev = N;
        if (N == 0) { pc('0'); pc('\n'); return ;}
        while ((rev % 10) == 0) { count++; rev /= 10;} //obtain the count of the number of 0s
        rev = 0;
        while (N != 0) { rev = (rev<<3) + (rev<<1) + N % 10; N /= 10;}  //store reverse of N in rev
        while (rev != 0) { pc(rev % 10 + '0'); rev /= 10;}
        while (count--) pc('0');
    }

Normally Printf is quite fast for outputs,however for writing Integer or Long Outputs,the below function is a tad bit faster.
Here we use the putchar_unlocked() method for outputting a character which is similar thread-unsafe version of putchar() and is faster.

See Link.

edited Jul 31 '22 at 18:16

ArekBulski

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answered Mar 16 '14 at 15:24

Dhruv Chandhok

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It checks only if the number have a '0' sequence at the end. This function doesn't work if the number have '0' sequences in the middle. ex.: 12300023 – 648trindade Sep 19 '15 at 15:40
@648trindade It Works. – Suraj Jain Feb 07 '17 at 13:19
Add the following to the beginning of the function to make it work for negative numbers: `if (n < 0) { pc('-'); n *= -1; }` – Björn Lindqvist Jan 04 '20 at 08:02

using putchar_unlocked for fast output

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