I have a problem in Linux programming about file read and write

This is a discussion on I have a problem in Linux programming about file read and write within the C Programming forums, part of the General Programming Boards category; If file is not exist,create it and write a string into it, else write a string into this file. but ...

  1. #1
    Registered User
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    Oct 2011
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    China
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    Red face I have a problem in Linux programming about file read and write

    If file is not exist,create it and write a string into it, else write a string into this file.

    but the problem is that open() return a bad file descriptor if this file is exist.

    code:

    Code:
    /*
    Linux Open() example source code
    Author:        Yucoat(www.yucoat.com)
    Data:        2011-10-31
    Version:    v0.1
    ChangeLog:    Create This program        2011-20-31
     */
    #include <fcntl.h>        //for open
    #include <errno.h>        //for errno
    #include <stdio.h>
    
    
    int main()
    {
        int fd;
    
    
        if ((fd = open(    "./Name",                                        //File name
                        O_WRONLY|O_EXCL|O_APPEND|O_CREAT,                //Mod
                        S_IRUSR|S_IWUSR|S_IRGRP|S_IWGRP|S_IROTH)) < 0)    //Access
        {
            perror("open");
            return -1;
        }
    
    
        if (write(fd, "Yucoat\n", 7) != 7)
            perror("Write");
        close (fd);
        return 0;
    }
    Thx for every body!I'm very sorry for my bad english!

  2. #2
    ATH0 quzah's Avatar
    Join Date
    Oct 2001
    Posts
    14,826
    Quote Originally Posted by thlgood View Post
    but the problem is that open() return a bad file descriptor if this file is exist.
    Of course it does. You told it to:
    Quote Originally Posted by thlgood View Post
    Code:
        if ((fd = open(    "./Name",                                        //File name
                        O_WRONLY|O_EXCL|O_APPEND|O_CREAT,                //Mod
    When in doubt, read the man page.


    Quzah.
    Hope is the first step on the road to disappointment.

  3. #3
    Registered User
    Join Date
    Oct 2011
    Location
    China
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    Yes I read it.

    But it's a big challenge for me to understand some man pages...

    Thx

  4. #4
    a_capitalist_story
    Join Date
    Dec 2007
    Posts
    2,649
    This
    O_EXCL error if create and file exists
    seems pretty crystal clear to me, considering your problem is
    the problem is that open() return a bad file descriptor if this file is exist.

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