C++读入神器——文操快读（oj也可以用）

当某天，本蒟蒻沉迷于卡常的时候：

我……

突然，YYKdalao说：用文操快读啊！

然后

喔～目瞪口呆

不多说，上源码：

本来用的读入方式：

inline void Read( int &x ) {
	x = 0; char ch = getchar();
	for( ; ch < '0' || ch > '9'; ch = getchar() );
	for( ; ch >= '0' && ch <= '9'; ch = getchar() )
		x = x * 10 + ch - '0';
	return;
}

文操快读：

const int MAX_SIZE = 1 << 15;
char *l, *r, buf[ MAX_SIZE ];
inline int gc() {
	if( l == r )
		if( l == ( r = ( l = buf ) + fread( buf, 1, MAX_SIZE, stdin ) ) ) return -1;
	return *l++;
}
inline void Read( int &x ) {
	char c = gc();
	for(; c < 48 || c > 57; c = gc() );
	for( x = 0; c > 47 && c < 58; c = gc() )
		x = ( x << 3 ) + ( x << 1 ) + ( c ^ 48 );
	return;
}

以下为2019.11.04 update

实际上，输出也同样可以使用 fwrite 加速。并且 fwrite 可以直接输出到屏幕上。（这与 fread 需要重定向stdin，或者用命令行里的< 不同。）更为方便的是，可以使用 sprintf 或者 vsnprintf 来方便地将一些内容写入字符数组中。下面贴上模板：

说明：你可以像 printf 和 scanf 一样使用里面的 Printf 和 Scanf 函数。但是 Scanf 函数的实现有些愚蠢（只能用%d表示一个int，并且不能有其他东西）。所以如果没有特殊需求的话最好用 Read 读取单个整数。你也可以自己写适合的 Read 函数。 输出流最后不一定需要 FlushOutput ，因为在销毁结构体的时候会执行这一步（这并不意味着你不需要fclose）。你可以通过更改 MAX_OUTPUT_ONCE 的值来更改 Printf 函数单次最大输出量。（如果超过了也许仍然能够正确输出，但那样会有一些不必要的错误。）

v0.1.0 之后提供了真正像scanf那样的读入方法。你可以用三句话实现（但是这仅仅是方便读入，并没有加速这个过程（fread带来的优化被memcpy抵消了QwQ））：

IO.Ready(); //预留足够的空间（至少为 MAX_INPUT_ONCE，不过你也需要保证一次读入的长度不超过 MAX_INPUT_ONCE）
sscanf(IO.It(), "...%n", ..., &IO.C); //读入
IO.Forward(); //刷新流，不然下一次读入会读重复的内容

注意: 结构体创建之后，就会从输入流中预读入。默认输入输出流是 stdin 和 stdout。所以不使用 FastIO 的时候请不要进行声明。

/*====================    Header : FastIO    ====================*/
/*====================     version 0.1.1     ====================*/
/*==================== Programed By chy-2003 ====================*/
/*
 * Logs :
 * version 0.1.1 : Fix bugs when flush input buffers
 * version 0.1.0 : Add new ways to read
 *     new    function char *It();
 *     new    function void Ready();
 *     new    function void Forward();
 *     You can read any thing like : but to make sure read less than MAX_INPUT_ONCE charactors once.
 *         IO.Ready();
 *         sscanf(IO.It(), "...%n", ..., &IO.C);
 *         IO.Forward();
 * version 0.0.1 : Update
 *     change function int GetChar();    : private -> public
 *     new    function int UnGetC();     : public (unget the last char. Return value 0:success; -1:fail)
 *     change function void Read(int &); : rewrite with UnGetC. will run UnGetC() after reading an integer
 * version 0.0.0 : Creat
 *     function 'Read' and 'Scanf' will return the number of values get successfully.
 *     function 'Read' :
 *         int Read(int&);
 *     funtion 'Scanf' :
 *         Warning : This funtion works in a stupid way
 *         int Scanf(const char *, ...);
 *         supports : all(just like printf);
 *
 *     funtion 'Printf' :
 *         Warning : Output may be cut off if the length longer than ((1 << 9) - 1), or you can set MAX_OUTPUT_ONCE equals to MAX_OUTPUT_BUFFER_SIZE
 *         void Printf(const char *, ...);
 *         supports : all(just like printf)
 */

#ifndef _MY_FASTIO_
#define _MY_FASTIO_

#include <cstdio>
#include <cstring>
#include <stdarg.h>

#define MAX_INPUT_BUFFER_SIZE (1 << 15)
#define MAX_OUTPUT_BUFFER_SIZE (1 << 15)
#define MAX_INPUT_ONCE (1 << 9)
#define MAX_OUTPUT_ONCE (1 << 9)
//notice : I check the buffer BEFORE every option.
//notice : please make sure MAX_INPUT_BUFFER_SIZE > 2 * MAX_INPUT_ONCE

struct FastIO {
//private:
    char *InputBufferLeft, *InputBufferRight, InputBuffer[MAX_INPUT_BUFFER_SIZE + 1];//The last position is for '\0'
    char OutputBuffer[MAX_OUTPUT_BUFFER_SIZE + 1]; // The last position is for '\0'
    int OutputBufferUsed;
    FILE *InputStream, *OutputStream;
    char cTemp;
    short iTemp;
    bool CanGet;

    inline void ClearInputBuffer();
    inline int GetFromInputStream();
    inline void SetInputBufferToLeft();
    inline bool EndOfFile();

public:
    int C;
    //Basic
    FastIO(FILE *_InputStream = stdin, FILE *_OutputStream = stdout);
    ~FastIO();

    //Input
    inline int GetChar();
    inline int UnGetC();
    inline int Read(int &x);
    inline int Scanf(const char *Format, ...);
    inline void Ready();
    inline void Forward();
    inline char *It();

    //Output
    inline void FlushOutput();
    inline void Printf(const char *Format, ...);
};

FastIO::FastIO(FILE *_InputStream, FILE *_OutputStream) :
    InputStream(_InputStream), OutputStream(_OutputStream),
    InputBufferLeft(InputBuffer), InputBufferRight(InputBuffer), OutputBufferUsed(0) {
        InputBuffer[MAX_INPUT_BUFFER_SIZE] = OutputBuffer[MAX_OUTPUT_BUFFER_SIZE] = '\0';
        CanGet = true;
        GetFromInputStream();
        return;
    }

FastIO::~FastIO() {
    FlushOutput();
    return;
}

inline void FastIO::ClearInputBuffer() {
    InputBufferLeft = InputBufferRight = InputBuffer;
    return;
}

inline int FastIO::GetFromInputStream() {
    if (!CanGet) return 1;
    char *Last = InputBufferRight;
    InputBufferRight = InputBufferRight + fread(InputBufferRight, 1, InputBuffer + MAX_INPUT_BUFFER_SIZE - InputBufferRight, InputStream);
    if (InputBufferRight == Last) CanGet = false;
    return !CanGet;
}

inline void FastIO::SetInputBufferToLeft() {
    memcpy(InputBuffer, InputBufferLeft, InputBufferRight - InputBufferLeft);
    InputBufferRight = InputBuffer + (InputBufferRight- InputBufferLeft);
    InputBufferLeft = InputBuffer;
    return;
}

inline int FastIO::GetChar() {
    if (InputBufferLeft == InputBufferRight) {
        ClearInputBuffer();
        if (GetFromInputStream()) return -1;
    }
    return *InputBufferLeft++;
}

inline int FastIO::Read(int &x) {
    cTemp = GetChar();
    iTemp = 1;
    for(; cTemp < 48 || cTemp > 57; cTemp = GetChar())
        if (cTemp == -1)
            return 0;
        else
            if (cTemp == '-')
                iTemp = -1;
    for(x = 0; cTemp > 47 && cTemp < 58; cTemp = GetChar())
        x = (x << 3) + (x << 1) + (cTemp ^ 48);
    UnGetC();
    x *= iTemp;
    return 1;
}

inline int FastIO::Scanf(const char *Format, ...) {
    int CountRead, Len, i, j;
    CountRead = 0;
    Len = strlen(Format);
    va_list ap;
    va_start(ap, Format);
    for (i = 0, j; i < Len; i = j + 1) {
        j = i;
        while (j + 1 < Len && Format[j + 1] != '%') ++j;
        if (j - i == 1 && Format[j] == 'd') {
            int *x;
            x = va_arg(ap, int *);
            Read(*x);
            ++CountRead;
        }
    }
    va_end(ap);
    return CountRead;
}

inline void FastIO::Ready() {
    if (InputBufferRight - InputBufferLeft < MAX_INPUT_ONCE && CanGet && (InputBufferRight - InputBuffer == MAX_INPUT_BUFFER_SIZE)) {
        SetInputBufferToLeft();
        GetFromInputStream();
    }
    return;
}

inline char *FastIO::It() {
    return InputBufferLeft;
}

inline void FastIO::Forward() {
    InputBufferLeft = InputBufferLeft + C;
    return;
}

inline void FastIO::FlushOutput() {
    if (OutputBufferUsed)
        fwrite(OutputBuffer, 1, OutputBufferUsed, OutputStream);
    OutputBufferUsed = 0;
    return;
}

inline void FastIO::Printf(const char *Format, ...) {
    if (OutputBufferUsed >= MAX_OUTPUT_BUFFER_SIZE - MAX_OUTPUT_ONCE)
        FlushOutput();
    va_list ap;
    va_start(ap, Format);
    OutputBufferUsed += vsnprintf(OutputBuffer + OutputBufferUsed, MAX_OUTPUT_BUFFER_SIZE - OutputBufferUsed, Format, ap);
    va_end(ap);
    return;
}

inline int FastIO::UnGetC() {
    if (InputBuffer != InputBufferLeft) {
        --InputBufferLeft;
        return 0;
    }
    return -1;
}

#undef MAX_INPUT_BUFFER_SIZE
#undef MAX_OUTPUT_BUFFER_SIZE
#undef MAX_INPUT_ONCE
#undef MAX_OUTPUT_ONCE

#endif

/*==================== End of Header : FastIO ====================*/