HELP! Reading from txt file and comparing to input

This is a discussion on HELP! Reading from txt file and comparing to input within the C Programming forums, part of the General Programming Boards category; Hey, possibly a bit of a noob question, i'm not quite sure... I have to create a sockets program that ...

  1. #1
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    Talking HELP! Reading from txt file and comparing to input

    Hey, possibly a bit of a noob question, i'm not quite sure...

    I have to create a sockets program that can identify clients and allow connection to the server based on their IP. I have created a text file that contains two "good" IP addresses:

    127.0.0.1
    127.0.0.2

    basically, i need to copy the IP of the potential client trying to connect (maybe hold it in a temp holder?), compare it to the values in the text file and allow or refuse the connection....however, as a new programmer I have pretty much no idea how to do this.

    The psuedocode as I understand it is as follows:
    <code>
    copy their_addr to temp holder(tempAdd)
    open "knownip.txt"
    while file != EOF
    if text line!= tempAdd
    go to next line
    if EOF -> refuse connection
    else if line==tempAdd
    connection allowed
    </code>

    this may not be accurate but it gives you the idea, any help on this would be very appreciated...

  2. #2
    Gawking at stupidity
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    Functions to look at:
    inet_ntoa()
    strcmp()
    fopen()
    fgets()
    fclose()

    The user's IP address will be stored in network byte order in the sin_addr member of the structure that you pass to accept().
    If you understand what you're doing, you're not learning anything.

  3. #3
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    thanks

    ok thanks, i've done a quick google search for a few of those functions and they look promising, i'll give them a try and see what happens.

  4. #4
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    Question

    ok, its taken a while but i've got it to read the first line from a text file and compare it to the connecting ip address. thats fine. however, i'm having trouble finding a way to loop so that it can check subsequent lines in the file if the first address doesnt match...i'm certain this is possible but can't find anywhere that explains how

    also, don't know whether this is possible, but then again it most probably is... i need to have the last login date for each user stored in the file next to their address. this needs to be read and then strings sent to the user from another file that fall within certain criteria , i.e. anything since they last logged in.

    very complicated explanation i know, but i can't simplify it any more. maybe there is a more efficient way of doing this? otherwise there is a lot of i/o and date calculations to perform....

  5. #5
    and the hat of wrongness Salem's Avatar
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    This loops, reading one line of the file at a time, until the end of the file is reached.
    Code:
    char buff[BUFSIZ];
    while ( fgets( buff, BUFSIZ, fp ) != NULL ) {
      /* do stuff */
    }
    Extract whatever you want out of the buff (print it, store it, etc) and let the loop read the next line from the file.

  6. #6
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    thanks for the help, could you tell me if using puts will put the text into the temp holder (temp_addr) or if i have to specify something more, like put buff in temp_addr?

    Code:
    FILE * pFile;
    
    pFile = fopen ("clients.txt", "r");
        if (pfile == NULL)
               perror("Error opening file"):
        else {
        while (fgets(buff, BUFSIZ, fp) != NULL) {
               puts (temp_addr);
               strcmp(temp_addr, theiraddr);
               fclose (pFile);
    
        }
    if !=0 {
        printf("Connection refused")
    else printf ("connection accepted")

  7. #7
    and the hat of wrongness Salem's Avatar
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    puts (temp_addr);
    Writes buff to stdout

    strcmp(temp_addr, theiraddr);
    compares two strings, then throws the answer away
    OK I suppose, but it doesn't really advance the program.

    fclose (pFile);
    Closes the file - are you sure you want to do this inside the loop - it's not much of a loop doing this here

  8. #8
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    some schoolboy errors there, oops!

    fixed them now, apart from "stdout", could you tell me how that works please?

    (temp_addr is a field i have defined to hold the value read from the text file so i can compare it to their_addr)

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