Fastest way to read input from stdin C++

Method 1 :

A noob's way :

#include <iostream> using namespace std; int main(){    int nb,a;    cin >> nb;    for (int i=0; i < nb; ++i){       cin >> a;       // do some stuff    }    return 0; }

Method 2 :

A classic way :

#include <iostream> using namespace std; int main(){    ios::sync_with_stdio(false);    cin.tie(nullptr);    int nb,a;    cin >> nb;    for (int i=0; i < nb; ++i){       cin >> a;       // do some stuff    }    return 0; }

Method 3 :

The C way :

#include <cstdio> int main(){    int nb,a;    scanf("%d",&nb);    for (int i=0; i < nb; ++i){       scanf("%d",&a);       // do something    }    return 0; }

Method 4 :

The getchar way :

#include <stdio.h> #include <stdlib.h> int fastscan(){    int c;    bool negative = false;    int a = 0;    c = getchar();    if (c=='-'){       negative = true;       c = getchar();    }    while(c>47 and c<58){       a = a*10 + c - 48;       c = getchar();    }    if(negative){       a = -a;    }    return a; } int main(){    int nb;    scanf("%d",&nb);    for (int i=nb; ~i; --i){       fastscan();       // do something    }    return 0; }

Method 5 :

The optimised getchar_unlocked method :

#include <stdio.h> #include <stdlib.h> inline int fastscan(){    int c;    bool negative = false;    int a = 0;    c = getchar_unlocked();    if (c=='-'){       negative = true;       c = getchar_unlocked();    }    while(c>47 and c<58){       a = (a<<1) + (a<<3) + (c - 48);       c = getchar_unlocked();    }    if(negative){       a = -a;    }    return a; } int main(){    int nb;    scanf("%d",&nb);    for (int i=nb; ~i; --i){       fastscan();       // do some stuff    }    return 0; }

Method 6 :

The inserter's way :

#include <iostream> #include <vector> #include <iterator> #pragma GCC optimize ("O3") using namespace std; int main(){    setvbuf(stdin, (char*)NULL, _IOFBF, 0);    ios::sync_with_stdio(false);    cout.tie(nullptr);    cin.tie(nullptr);    int nb;    cin >> nb;    vector<int> v;    copy(istream_iterator<int>(cin), istream_iterator<int>(),back_inserter(v));    for (auto& i:v) // do some operations    return 0; }

Method 7 :

The bufferer's way :

#include <iostream> #define BUFSIZE 1024*900*64 int main(){    int n, number=0,numbers;    scanf("%d",&n);    char buf[BUFSIZE+1] = {0};    while ((numbers = fread(buf, 1, BUFSIZE, stdin)) > 0){      bool neg=false;       for (int i=0; i < numbers; i++){       if (buf[i] == '-') neg=true;       else if (buf[i] != '\n'){          number = buf[i] - '0' + 10*number;       }        else{          n--;          if (neg) number = -number;          // do something          number = 0;          neg = false;        }            }      if (!n)  break;    } }

Method 8 :

The ultimate way :

#include <cstdint> #include <cstdlib> #include <cstdio> #include <unistd.h> #include <sys/mman.h> #include <sys/stat.h> inline char* stdin_ptr(){     struct stat sb;     (void)fstat( STDIN_FILENO, &sb );     return (char*)mmap (0, sb.st_size, PROT_READ, MAP_SHARED | MAP_POPULATE, STDIN_FILENO, 0); } inline int atoi(char*& data){     int val = 0;     bool neg=false;     if (*data == '-'){        neg = true;        data++;     }     do{         val = val*10 + *data++ - '0';     } while(*data & (1<<4));     if (neg) val = -val;     ++data;     return val; } int main(){     char* ptr = stdin_ptr();     int n = atoi(ptr);     while (*ptr) // do something }

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