输出重定向可分离

 stdout -> 1
    printf("hello printf 1\n");
    fprintf(stdout,"hello fprintf 1\n");
    // stderr -> 2
 
    errno = 1;
    perror("hello perror 2"); //stderr

    const char *s1 = "hello write 1\n";
    write(1, s1, strlen(s1));

    const char *s2 = "hello write 2\n";
    write(2, s2, strlen(s2));

    // cout -> 1
    std::cout << "hello cout 1" << std::endl;
    // cerr -> 2
    std::cerr << "hello cerr 2" << std::endl;



    close(1);
    int fd = open("log.txt", O_WRONLY | O_CREAT | O_TRUNC, 0666);
    if(fd < 0)
    {
        perror("open");
        return 0;
    }

自定义perror

#include <iostream>
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>

void myperror(const char *msg)
{
    fprintf(stderr, "%s: %s\n", msg, strerror(errno));
}


int main()
{
    int fd = open("log.txt", O_RDONLY);
    if(fd < 0)
    {
        myperror("open");
        return 1;
    }
}

磁盘文件+inode

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