how to use getchar_unlocked()

general
,
1

I’m totally new in this,I really don’t know how to use this. I’ve googled it,but I’ve got some methods with getchar_unlocked method() somthing like dat

    #define getchar_unlocked gc()
void scanint(int &x)
{
    register int c = gc();
    x = 0;
    for(;(c<48 || c>57);c = gc());
    for(;c>47 && c<58;c = gc()) {x = (x<<1) + (x<<3) + c - 48;}
}

or

#define getcx getchar_unlocked
inline void inp( int &n )//fast input function
{
   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;
}

but didn’t get it at all. If I wanna take input char,int,long and long long int, can I use getchar_unlocked( ) for faster input?I’m getting TLE for a problem. please help me how to take input for int,char,long,long long int int c++.
Thnq :slight_smile:

1 Like
2

Hi @tictactoecoder! Yes you can do that. Just change the data type of the value you’re passing in to this function to the data type you want to scan.

3

Brother, all the standard functions you use for IO are thread safe. Hence they need to lock mutexes and prevent simultaneous access to the buffer. getchar_unlocked is not thread safe. Hence all the overheads of mutual exclusion is avoided. But as we have a single thread it doesn’t matter for us. check more here. The getchar_unlocked() function gets a character from stdin. It is equivalent to getc_unlocked(stdin). It is used for faster i/o by removing the input stream lock check. But at the same time removing input stream lock check make it unsafe as well.

3 Likes