using /dev/urandom multiple times

This is a discussion on using /dev/urandom multiple times within the C Programming forums, part of the General Programming Boards category; I want to get a value from /dev/urandom and use the value, then assign a new value from /dev/urandom to ...

  1. #1
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    using /dev/urandom multiple times

    I want to get a value from /dev/urandom and use the value, then assign a new value from /dev/urandom to the same variable and use that new value. This will be done in an if inside a while-loop that will keep repeting

    I have tried using:
    Code:
    fp = fopen("/dev/random", "r");
    fclose(fp);
    and freopen() as well, but neither work

    I end up with something like this:
    Code:
    fp = fopen("/dev/random", "r");
    value = (int)fp;
    printf("%d", value); //if this prints 25
    fclose(fp);
    
    fp = fopen("/dev/random", "r");
    value = (int)fp;
    printf("%d", value); //then this prints 25
    fclose(fp);
    I want the second value to be completly different, and also random

  2. #2
    ATH0 quzah's Avatar
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    Why are you doing this:
    Code:
    value = (int)fp;
    You're taking the value of the file pointer itself, not anything in the file. You're basically doing this:
    Code:
    int *foo;
    int bar = (int) foo;
    bar = (int) foo;
    bar = (int) foo;
    And wondering why they're all the same value.


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

  3. #3
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    And since I am using a pointer do I use fscanf to get data instead?

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    Quote Originally Posted by miutsu View Post
    And since I am using a pointer do I use fscanf to get data instead?
    Actually I realy want a description of how to get these values since I plan on using them in a program to provide randomness

  5. #5
    ATH0 quzah's Avatar
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    Cprogramming.com FAQ > Work with files (C)

    Read the FAQ on working with files. Or the section of your book that covers it.


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

  6. #6
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    I think you need to use fread(). man page fread section 3

  7. #7
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    Quote Originally Posted by Bayint Naung View Post
    I think you need to use fread(). man page fread section 3
    Thank you, that worked
    I used:
    Code:
    fp = fopen("/dev/urandom", "r");
    fread(&random, sizeof(int), 1, fp);
    random = abs(random);
    and it worked perfectly, but I dont have any man pages on fread or any other C functions, do you know where I could download those, I have Ubuntu.

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