A template for fast read of integer and string for c++.

gistfile1.cpp

/*
 * $File: fast-read.cc
 * $Date: Fri Dec 21 14:44:05 2012 +0800
 * $Author: Xinyu Zhou <zxytim[at]gmail[dot]com>
 *
 * A template for fast read of integer and string.
 *
 * This implementation is in MACRO format because it
 * yields a slightly faster code that that of using
 * function calls.
 *
 * This version of code uses a fixed size buffer to store
 * inputs by *fread*, and analyze the string manually to convert it
 * to int or string. Also, update the buffer when it is exhausted.
 *
 * sample usage:
 *    READ_INT(num);
 *    READ_STR(str); // str is a char*, which no boundary checking
 */

/* {{{ fast read*/
#include <cstdio>
#include <cctype>
FILE *fast_read_fin = stdin;

const int N_BUF_MAX = 10000;
char fast_read_buffer[N_BUF_MAX];
char *fast_read_ptr = fast_read_buffer + N_BUF_MAX,
     *fast_read_buf_end = fast_read_buffer + N_BUF_MAX;

#define PTR_NEXT() \
    do { \
        if (fast_read_ptr != fast_read_buf_end) \
            break; \
        fast_read_ptr = fast_read_buffer; \
        fread(fast_read_buffer, N_BUF_MAX, 1, fast_read_fin); \
    } while (0)

#define READ_INT(__num__)  \
    do { \
        int ret = 0, sign = 1; \
        for (; ;) \
        { \
            PTR_NEXT(); \
            if (isdigit(*fast_read_ptr) || (*fast_read_ptr) == '-') \
                break; \
            fast_read_ptr ++; \
        } \
        if ((*fast_read_ptr) == '-') \
        { \
            sign = -1; \
            fast_read_ptr ++; \
        } \
        for (; ;) \
        { \
            PTR_NEXT(); \
            if (!isdigit(*fast_read_ptr)) \
                break; \
            ret = ret * 10 + (*(fast_read_ptr ++)) - '0'; \
        } \
        (__num__) = ret * sign; \
    } while (0)

#define READ_STR(__str__) \
    ({ \
        char *start = (__str__), \
             *ret = start; \
        do { \
            for (; ;) \
            { \
                PTR_NEXT(); \
                if (!isspace(*fast_read_ptr)) \
                    break; \
                fast_read_ptr ++; \
            } \
            for (; ;) \
            { \
                PTR_NEXT(); \
                if (isspace(*fast_read_ptr)) \
                    break; \
                *(ret ++) = *(fast_read_ptr ++); \
            } \
            (*ret) = 0; \
        } while (0); \
        ret - start; \
    })
/* }}}*/

int main()
{
    int a, b;
    READ_INT(a);
    READ_INT(b);
    printf("%d\n", a + b);
    return 0;
}

/**
 * vim: syntax=cpp11 foldmethod=marker
 */