fast_io.c

#include <unistd.h>

#define BUF_MAX (4 * 1024)
int read_char(void) {
    static char buf[BUF_MAX];
    static unsigned int size = 0;
    static unsigned int ptr = 0;
    if (ptr == size) {
        size = read(0, buf, BUF_MAX);
        ptr = 0;
        if (size == 0)
            return -1;
    }
    return buf[ptr++];
}

int read_int(void) {
    int ret = 0;
    int rd = read_char();
    while (rd < '0' || '9' < rd) {
        rd = read_char();
        if (rd == -1)
            return -1;
    }
    while ('0' <= rd && rd <= '9') {
        ret = 10 * ret + rd - '0';
        rd = read_char();
    }
    return ret;
}

static char wbuf[BUF_MAX];
static int wptr = 0;
void write_char(int c) {
    wbuf[wptr++] = c;
    if (wptr == BUF_MAX) {
        write(1, wbuf, BUF_MAX);
        wptr = 0;
    }
}

void write_int(int a) {
    char ibuf[20];
    int i = 0;
    while (a > 0) {
        ibuf[i++] = a % 10;
        a = a / 10;
    }
    --i;
    while (i >= 0) {
        write_char(ibuf[i] + '0');
        --i;
    }
}

void write_flush(void) {
    write(1, wbuf, wptr);
    wptr = 0;
}

int main(void) {
    int a = read_int();
    while (a != -1) {
        write_int(a);
        write_char('\n');
        a = read_int();
    }
    write_flush();
}