太一的博客

一个程序学徒

文件与IO（二）

stat

功能：读取文件元数据

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int stat(const char *path, struct stat *buf);
int fstat(int fd, struct stat *buf);
int lstat(const char *path, struct stat *buf);

struct stat

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struct stat {
  dev_t st_dev; /* ID of device containing file */
  ino_t st_ino;	/* inode number */
  mode_t st_mode; /* protection */
  nlink_t st_nlink /* number of hard links */
}

复制文件描述符

复制文件描述符有三种方法

​ dup

​ dup2

​ fcntl

fcntl(fd, F_DUPFD, fd_start);

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#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <dirent.h>

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>

int filetype(struct stat *buf);
#define ERR_EXIT(m) \
        do \
        { \
                perror(m); \
                exit(EXIT_FAILURE); \
        } while(0)

int main(int argc, char *argv[])
{
    int fd;
    fd = open("test2.txt", O_WRONLY);
    if (fd == -1)
        ERR_EXIT("open error");
    close(1);
    dup(fd);
    printf("1111\n");
    return 0;
}

fcntl

功能：操纵文件描述符，改变已打开的文件的属性

int fcntl(int fd, int cmd, ... /* arg */ );

fcntl 常用操作

  • 复制文件描述符
    • F_DUPFD (long)
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#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <dirent.h>

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>

int filetype(struct stat *buf);
#define ERR_EXIT(m) \
        do \
        { \
                perror(m); \
                exit(EXIT_FAILURE); \
        } while(0)

int main(int argc, char *argv[])
{
    int fd;
    fd = open("test.txt", O_WRONLY);
    if (fd == -1)
        ERR_EXIT("open error");
    // close(1);
    // dup(fd);
    close(1);
    if (fcntl(fd, F_DUPFD, 0) < 0)
        ERR_EXIT("dup fd error");
    printf("1111xx\n");
    return 0;
}

  • 文件描述符标志
    • F_GETFD (void)
    • F_SETFD (long)
  • 文件状态标志
    • F_GETFL (void)
    • F_SETFL (long)
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#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <dirent.h>

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>

int filetype(struct stat *buf);
#define ERR_EXIT(m) \
        do \
        { \
                perror(m); \
                exit(EXIT_FAILURE); \
        } while(0)

int main(int argc, char *argv[])
{
    char buf[1024] = {0};
    int ret;
    int flags;
    flags = fcntl(0, F_GETFL, 0);
    if (flags == -1)
        ERR_EXIT("fcntl get flag error");
    
    ret = fcntl(0, F_SETFL, flags | O_NONBLOCK);
    if (ret == -1)
        ERR_EXIT("fcntl set flag error");

    ret = read(0, buf, 1024);
    if (ret == -1)
        ERR_EXIT("read error");
    
    printf("buf=%s\n", buf);

}
  • 文件锁
    • F_GETLK
    • F_SETLK, F_SETLKW
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struct flock {
	short l_type;
	short l_whence;
  off_t l_start;
  off_t l_len;
  pid_t l_pid;
};
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#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <dirent.h>

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>

int filetype(struct stat *buf);
#define ERR_EXIT(m) \
        do \
        { \
                perror(m); \
                exit(EXIT_FAILURE); \
        } while(0)

int main(int argc, char *argv[])
{
    int fd;
    fd = open("test2.txt", O_CREAT | O_RDWR | O_TRUNC, 0644);
    if (fd == -1)
        ERR_EXIT("open error");
    
    struct flock lock;
    memset(&lock, 0, sizeof(lock));
    lock.l_type = F_WRLCK;
    lock.l_whence = SEEK_SET;
    lock.l_start = 0;
    lock.l_len = 0;

    if (fcntl(fd, F_SETLK, &lock) == 0)
    {
        printf("lock succes\n");
        printf("press any key to unlock\n");
        getchar();
        lock.l_type = F_UNLCK;
        if (fcntl(fd, F_SETLK, &lock) == 0)
            printf("unlock success\n");
        else
            ERR_EXIT("unlock fail");
    }
    else
        ERR_EXIT("lock fail");
    

}