C语言UNIX系统接口-低级IO-read和write-默认标准IO

0 标准输入
1 标准输出
2 标准错误

int n_read = read(int fd, char *buf, int n);
int n_write = write(int fd, char *buf, int n);

#include "stdio.h"
#include "unistd.h"

#define BUF 6

void copy01();
int getchar01();
int getchar02();

int main()
{
    copy01();

    char c;
    c = getchar01();
    printf("%c\n", c);
    c = getchar01(); // 等待read
    printf("%c\n", c);

    c = getchar02();
    printf("%c\n", c);
    c = getchar02();
    c = getchar02();
    c = getchar02(); // 要么从缓存里面取，要么等待read
    c = getchar02();
    c = getchar02();
    c = getchar02();
    printf("%c\n", c);

    // 注明： 如果把getchar02放到01前面执行，02会一次性尽量读取BUFSIZE512个字符，
    //       会发现01要等待第二次的标准输入。
    return 0;
}

/* 复制标准输入到标准输出 */
void copy01(void)
{
    char exit0 = '0';
    char buf[BUF];
    int n;
    printf("请输入内容，回车结束。输入0时，退出复制。\n");
    while ((n = read(0, buf, BUF)) > 0)
    {
        if (buf[0] == exit0)
        {
            printf("退出。\n");
            break;
        }
        write(1, buf, n);
    }
}

/* 不带缓冲的getchar */
int getchar01(void)
{
    char c;
    return (read(0, &c, 1) == 1) ? (unsigned char)c : EOF;
}

/* 带缓冲的getchar */
int getchar02(void)
{
    static char buf[BUFSIZ];
    static char *bufp = buf;
    static int n = 0;
    if (n == 0)
    {
        n = read(0, buf, sizeof(buf));
        bufp = buf;
    }
    return (--n >= 0) ? (unsigned char)*bufp++ : EOF;
}