Linux _文件操作demo

main1.c

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

int main(void)
{
    int i;

    char buff[] = "hello world
";
    write(1, buff, sizeof(buff));
    write(2, buff, sizeof(buff));

    return 0;
}

main2.c

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

int main(void) 
{
    char buff[1024];
    int cnt;

    cnt = read(0, buff,  sizeof(buff));
    write(1, buff, cnt);

    return 0;
}

main3.c

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

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


#define FILE1_NAME "shell_program.pdf"
#define FILE2_NAME "shell_program2.pdf"

int main(void)
{
    int file1, file2;
    char c;

    file1 = open(FILE1_NAME, O_RDONLY);
    if (file1 < 0) {
        printf("open file %s failed
", FILE1_NAME);
    }

    file2 = open(FILE2_NAME, O_WRONLY|O_CREAT, S_IRUSR|S_IWUSR);
    if (file1 < 0) {
        printf("open file %s failed
", FILE2_NAME);
    }

    while(read(file1, &c, 1) == 1) {
        write(file2, &c, 1);
    }

    return 0;
}

main4.c

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

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


#define FILE1_NAME "shell_program.pdf"
#define FILE2_NAME "shell_program2.pdf"

int main(void)
{
    int file1, file2;
    //char c;
    char buff[1024];
    int ret;

    file1 = open(FILE1_NAME, O_RDONLY);
    if (file1 < 0) {
        printf("open file %s failed
", FILE1_NAME);
    }

    file2 = open(FILE2_NAME, O_WRONLY|O_CREAT, S_IRUSR|S_IWUSR);
    if (file1 < 0) {
        printf("open file %s failed
", FILE2_NAME);
    }

    while((ret = read(file1, buff, sizeof(buff))) > 0) {
        write(file2, buff, ret);
    }

    return 0;
}

main5.c

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

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


#define FILE1_NAME "main5.c"
#define FILE2_NAME "main5_2.c"

#define SIZE 50

int main(void)
{
    int file1, file2;
    //char c;
    char buff[1024];
    int ret;

    file1 = open(FILE1_NAME, O_RDONLY);
    if (file1 < 0) {
        printf("open file %s failed
", FILE1_NAME);
    }

    file2 = open(FILE2_NAME, O_WRONLY|O_CREAT, S_IRUSR|S_IWUSR);
    if (file1 < 0) {
        printf("open file %s failed
", FILE2_NAME);
    }

    lseek(file1, -SIZE, SEEK_END);

    while((ret = read(file1, buff, SIZE)) > 0) {
        write(file2, buff, ret);
    }

    return 0;
}

main6.c

#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>




#define FILE_NAME   "test.txt"


int flock_set(int fd, int type)
{
    printf("pid=%d into...
", getpid());

    struct flock flock;
    flock.l_type = type;
    flock.l_whence = SEEK_SET;
    flock.l_start = 0;
    flock.l_len = 0;   
    flock.l_pid = -1;

    fcntl(fd, F_GETLK, &flock);

    if (flock.l_type != F_UNLCK) {
        if (flock.l_type == F_RDLCK) {
            printf("flock has been set to read lock by %d
", flock.l_pid);
        } else if (flock.l_type == F_WRLCK) {
            printf("flock has been set to write lock by %d
", flock.l_pid);
        }
    }

    flock.l_type = type;
    if (fcntl(fd, F_SETLKW, &flock) < 0) {
        printf("set lock failed!
");
        return -1;
    }   

    switch (flock.l_type) {
    case F_RDLCK:
        printf("read lock is set by %d
", getpid());
        break;
    case F_WRLCK:
        printf("write lock is set by %d
", getpid());
        break;
    case F_UNLCK:
        printf("lock is released by %d
", getpid());
        break;
    default:
        break;
    }

    printf("pid=%d out.
", getpid());
    return 0;
}

int main(void)
{
    int fd;

    fd = open(FILE_NAME, O_RDWR|O_CREAT, 0666);
    if (fd < 0) {
        printf("open file %s failed!
", FILE_NAME);
    }

    //flock_set(fd, F_WRLCK);
    flock_set(fd, F_RDLCK);
    getchar();
    flock_set(fd, F_UNLCK);
    getchar();

    close(fd);
    return 0;
}