getchar_unlocked()

Hey every1,
i see every1 uses getchar_unlocked()for accepting 2 space separated integers.
Can any1 please tell me how this function works and how to use it(detailed) because i dont know anything bout this funtion

Thanks in advance
Daksh

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long long int read_int(){
char r;
bool start=false,neg=false;
long long int ret=0;
while(true){
r=getchar();
if((r-‘0’<0 || r-‘0’>9) && r!=’-’ && !start){
continue;
}
if((r-‘0’<0 || r-‘0’>9) && r!=’-’ && start){
break;
}
if(start)ret*=10;
start=true;
if(r==’-’)neg=true;
else ret+=r-‘0’;
}
if(!neg)
return ret;
else
return -ret;
}

Well , first of all you shouldn’t be using getchar_unlocked() as it is a thread unsafe version of getchar(). People using them are just trying to get a little more faster execution of the program . Rather than that , focus more on the algorithms you need to implement to solve the particular problem , and according the problem specifications , try to get a faster algorithm .

A simple implementation of getchar_unlocked() to take an int as an input will be as follows:-

#define getcx getchar_unlocked

 inline void inp( int &n ) 
 {
    n=0;
    int ch=getcx();int sign=1;
    while( ch < '0' || ch > '9' ){if(ch=='-')sign=-1; ch=getcx();}

    while(  ch >= '0' && ch <= '9' )
            n = (n<<3)+(n<<1) + ch-'0', ch=getcx();
    n=n*sign;
  }   

So if you know how getchar(); works that is taking the character from the input and putting it into the respective variable , it’s the same for getchar_unlocked().
As speed goes
getchar_unlocked() > getchar() > scanf() > cin .
More could be learnt from here.

Amazing.
Thank for sharing the great help that is valuable.

@admin and others-

I am afraid that this jonclark007 guy seems to be spamming. (the website he shared is related to some research paper writing for students)

Please look into it @admin :slight_smile:

Why have you tagged this question as both easy and hard simultaneously?

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