I decided to rewrite this post, previously has been deleted.↵
↵
I know there a many of posts low-level i/o. ↵
↵
scanf/printf solves slowly i/o, partially, but not always. ↵
↵
Most generic usage i/o — is read and write integers, so I'll write about it without a hundred lines of source code.↵
↵
1. Read integers.↵
===================↵
↵
For simplicity, all input file content loaded to a big buffer, and it will be parsed.↵
↵
↵
~~~~~↵
↵
char in[1<<23] ; // a big buffer↵
char const* o ; // pointer to buffer.↵
~~~~~↵
↵
And for detecting end of buffer, put '\0' — terminating symbol to end of buffer ( as plain c-string).↵
#### Now loading the file:↵
↵
↵
~~~~~↵
void load(){ o = in; in [ fread(in, 1, sizeof(in ) - 4 , stdin ) ] = 0; }↵
~~~~~↵
`fread - returns number of reading symbols, we just use this for put '\0' terminating symbol to end of buffer.`↵
↵
↵
#### Reading a unsigned integer:↵
↵
↵
~~~~~↵
unsigned readUInt(){↵
unsigned u = 0;↵
↵
while( *o && *o <= 32) ++o ; // skip spaces↵
↵
while ( *o >='0' && *o <='9') u = (u << 3) + (u << 1) + (*o++ -'0');↵
return u;↵
}↵
~~~~~↵
↵
By default most implementations used `u = u * 10 + (*o++ - '0')`, ↵
but `u * 10 = u * 8 + u * 2 = (u << 3) + (u <<1)`↵
I don't know it gives speed, but with shifting the code become happy :) ↵
↵
#### Reading signed integer.↵
↵
Some theory of signed integer representation, in most situation [see here](https://en.wikipedia.org/wiki/Signed_number_representations) ↵
↵
` -u == ~u + 1 `↵
↵
There **~** — bitwise inverting.↵
↵
And↵
` ~u == u ^ 0xFFFFFFFF ` or ` ~u == u ^ ~0 `↵
↵
Let start writing method↵
↵
~~~~~↵
int readInt()↵
{↵
unsigned u = 0, s = 0; // s = 0, if integer positive, s = ~0 - if integer negative↵
while(*o && *o <= 32)++o; // skip spaces↵
↵
if (*o == '-')s = ~0, ++o; else if (*o == '+') ++o; // determine sign↵
while( *o >='0' && *o <= '9') u = (u << 3) + (u << 1) + (*o ++ - '0');↵
↵
return (u^s) + !!s; // ??????? : s = 0 : (u^s) + !!s = (u^0) + !!0 = u + 0 = u, and↵
// s = ~0: (u^s) + !!s = (u ^ ~0) + !! ~0 = (u^0xFFFFFFFF) + 1 = ~u + 1 = -u↵
↵
}↵
~~~~~↵
↵
↵
↵
↵
How to use this complete?↵
↵
↵
~~~~~↵
#include <cstdio>↵
↵
char const * o;↵
char in[1<<23];↵
↵
void load(){ o = in ; in [ fread(in,1,sizeof(in)-4,stdin)] = 0; }↵
unsigned readUInt(){↵
unsigned u = 0;↵
while(*o && *o <= 32)++o;↵
while(*o >='0' && *o <='9') u = (u << 3) + (u << 1) + (*o++ -'0');↵
return u;↵
}↵
int readInt(){↵
unsigned u = 0, s = 0;↵
while(*o && *o <= 32)++o;↵
if (*o == '-') s = ~0, ++o; else if(*o == '+') ++o;↵
while(*o >='0' && *o <='9') u = (u << 3) + (u << 1) + (*o++ - '0');↵
↵
return (u ^ s) + !!s;↵
}↵
↵
int main()↵
{↵
load();↵
int n = readInt();↵
int s = 0;↵
for(int i= 0; i < n; ++i)s += readInt();↵
↵
printf("summa = %d\n", s);↵
↵
return 0;↵
}↵
~~~~~↵
↵
Compare low-level i/o: [submission:24139587] with std::cin , std::cout [submission:24133798]↵
↵
### Benchmark: read and write 10^6 numbers took [120~150 milliseconds](https://github.com/raidenluikang/algorithms/tree/master/fastio) where scanf/printf ~650 milliseconds.↵
↵
for competetive programming this single method is enough for reading integers:↵
------------------------------------------------------↵
↵
↵
~~~~~↵
typedef long long ll;↵
typedef unsigned long long ull;↵
↵
ll readInt(){↵
ull u = 0 , s = 0;↵
while(*o && *o <= 32)++o;↵
if (*o == '-') s = ~s, ++o; else if (*o == '+') ++o;↵
while(*o >='0' && *o<='9') u = (u << 3) + (u << 1) + (*o++ -'0');↵
↵
return (u ^ s) +!!s; ↵
}↵
~~~~~↵
↵
↵
-----------------------------------------------------------------------------------------------------------↵
↵
2. Writing integers.↵
====================↵
↵
There are need a big buffer and pointer, again.↵
↵
↵
~~~~~↵
typedef long long ll;↵
char out[1<<23];↵
char * w = out; // initialize with &out[0] - beginning of the buffer.↵
~~~~~↵
↵
↵
There a single **writeInt** method, arguments: integer `u` and serarator `c` . ↵
↵
↵
~~~~~↵
// need to implement this method.↵
void writeInt( ll u, char separator); // u - integer, separator - will printed after the integer, most situations is space, or '\n'.↵
~~~~~↵
↵
**AND flush method, which we must call at the end of all operations.**↵
↵
↵
~~~~~↵
// flush - must be called before end of program.↵
void flush(){ fwrite(out, 1, w - out, stdout); }↵
~~~~~↵
↵
↵
↵
For implementing **writeInt** need temporary buffer :↵
↵
↵
~~~~~↵
void writeInt(ll u, char separator)↵
{↵
char tmpbuf[20]; int i;↵
if ( u < 0 ){ *w ++ = '-'; u = - u ; }↵
i = 20;↵
do tmpbuf[--i] = u % 10 + '0'; while(u/=10); // write last digits of u to tmpbuf from end to begin.↵
↵
// now write tmpbuf to out[] buffer from w pointer.↵
do *w++ = tmpbuf[i++]; while(i < 20);↵
↵
// and separator↵
*w++ = separator;↵
}↵
~~~~~↵
↵
↵
It's all.↵
↵
↵
↵
↵
↵
↵
I know there a many of posts low-level i/o. ↵
↵
scanf/printf solves slowly i/o, partially, but not always. ↵
↵
Most generic usage i/o — is read and write integers, so I'll write about it without a hundred lines of source code.↵
↵
1. Read integers.↵
===================↵
↵
For simplicity, all input file content loaded to a big buffer, and it will be parsed.↵
↵
↵
~~~~~↵
↵
char in[1<<23] ; // a big buffer↵
char const* o ; // pointer to buffer.↵
~~~~~↵
↵
And for detecting end of buffer, put '\0' — terminating symbol to end of buffer ( as plain c-string).↵
#### Now loading the file:↵
↵
↵
~~~~~↵
void load(){ o = in; in [ fread(in, 1, sizeof(in ) - 4 , stdin ) ] = 0; }↵
~~~~~↵
`fread - returns number of reading symbols, we just use this for put '\0' terminating symbol to end of buffer.`↵
↵
↵
#### Reading a unsigned integer:↵
↵
↵
~~~~~↵
unsigned readUInt(){↵
unsigned u = 0;↵
↵
while( *o && *o <= 32) ++o ; // skip spaces↵
↵
while ( *o >='0' && *o <='9') u = (u << 3) + (u << 1) + (*o++ -'0');↵
return u;↵
}↵
~~~~~↵
↵
By default most implementations used `u = u * 10 + (*o++ - '0')`, ↵
but `u * 10 = u * 8 + u * 2 = (u << 3) + (u <<1)`↵
I don't know it gives speed, but with shifting the code become happy :) ↵
↵
#### Reading signed integer.↵
↵
Some theory of signed integer representation, in most situation [see here](https://en.wikipedia.org/wiki/Signed_number_representations) ↵
↵
` -u == ~u + 1 `↵
↵
There **~** — bitwise inverting.↵
↵
And↵
` ~u == u ^ 0xFFFFFFFF ` or ` ~u == u ^ ~0 `↵
↵
Let start writing method↵
↵
~~~~~↵
int readInt()↵
{↵
unsigned u = 0, s = 0; // s = 0, if integer positive, s = ~0 - if integer negative↵
while(*o && *o <= 32)++o; // skip spaces↵
↵
if (*o == '-')s = ~0, ++o; else if (*o == '+') ++o; // determine sign↵
while( *o >='0' && *o <= '9') u = (u << 3) + (u << 1) + (*o ++ - '0');↵
↵
return (u^s) + !!s; // ??????? : s = 0 : (u^s) + !!s = (u^0) + !!0 = u + 0 = u, and↵
// s = ~0: (u^s) + !!s = (u ^ ~0) + !! ~0 = (u^0xFFFFFFFF) + 1 = ~u + 1 = -u↵
↵
}↵
~~~~~↵
↵
↵
↵
↵
How to use this complete?↵
↵
↵
~~~~~↵
#include <cstdio>↵
↵
char const * o;↵
char in[1<<23];↵
↵
void load(){ o = in ; in [ fread(in,1,sizeof(in)-4,stdin)] = 0; }↵
unsigned readUInt(){↵
unsigned u = 0;↵
while(*o && *o <= 32)++o;↵
while(*o >='0' && *o <='9') u = (u << 3) + (u << 1) + (*o++ -'0');↵
return u;↵
}↵
int readInt(){↵
unsigned u = 0, s = 0;↵
while(*o && *o <= 32)++o;↵
if (*o == '-') s = ~0, ++o; else if(*o == '+') ++o;↵
while(*o >='0' && *o <='9') u = (u << 3) + (u << 1) + (*o++ - '0');↵
↵
return (u ^ s) + !!s;↵
}↵
↵
int main()↵
{↵
load();↵
int n = readInt();↵
int s = 0;↵
for(int i= 0; i < n; ++i)s += readInt();↵
↵
printf("summa = %d\n", s);↵
↵
return 0;↵
}↵
~~~~~↵
↵
Compare low-level i/o: [submission:24139587] with std::cin , std::cout [submission:24133798]↵
↵
### Benchmark: read and write 10^6 numbers took [120~150 milliseconds](https://github.com/raidenluikang/algorithms/tree/master/fastio) where scanf/printf ~650 milliseconds.↵
↵
for competetive programming this single method is enough for reading integers:↵
------------------------------------------------------↵
↵
↵
~~~~~↵
typedef long long ll;↵
typedef unsigned long long ull;↵
↵
ll readInt(){↵
ull u = 0 , s = 0;↵
while(*o && *o <= 32)++o;↵
if (*o == '-') s = ~s, ++o; else if (*o == '+') ++o;↵
while(*o >='0' && *o<='9') u = (u << 3) + (u << 1) + (*o++ -'0');↵
↵
return (u ^ s) +!!s; ↵
}↵
~~~~~↵
↵
↵
-----------------------------------------------------------------------------------------------------------↵
↵
2. Writing integers.↵
====================↵
↵
There are need a big buffer and pointer, again.↵
↵
↵
~~~~~↵
typedef long long ll;↵
char out[1<<23];↵
char * w = out; // initialize with &out[0] - beginning of the buffer.↵
~~~~~↵
↵
↵
There a single **writeInt** method, arguments: integer `u` and serarator `c` . ↵
↵
↵
~~~~~↵
// need to implement this method.↵
void writeInt( ll u, char separator); // u - integer, separator - will printed after the integer, most situations is space, or '\n'.↵
~~~~~↵
↵
**AND flush method, which we must call at the end of all operations.**↵
↵
↵
~~~~~↵
// flush - must be called before end of program.↵
void flush(){ fwrite(out, 1, w - out, stdout); }↵
~~~~~↵
↵
↵
↵
For implementing **writeInt** need temporary buffer :↵
↵
↵
~~~~~↵
void writeInt(ll u, char separator)↵
{↵
char tmpbuf[20]; int i;↵
if ( u < 0 ){ *w ++ = '-'; u = - u ; }↵
i = 20;↵
do tmpbuf[--i] = u % 10 + '0'; while(u/=10); // write last digits of u to tmpbuf from end to begin.↵
↵
// now write tmpbuf to out[] buffer from w pointer.↵
do *w++ = tmpbuf[i++]; while(i < 20);↵
↵
// and separator↵
*w++ = separator;↵
}↵
~~~~~↵
↵
↵
It's all.↵
↵
↵
↵
↵
↵
