Dev Urandom Example C

11.06.2020by
  1. Dev Urandom Example C V
  2. Urandom Warning
  3. /dev/urandom C++

The character special files /dev/random and /dev/urandom (present since Linux 1.3.30) provide an interface to the kernel's random number generator. The file /dev/random has major device number 1 and minor device number 8. The file /dev/urandom has major device number 1 and minor device number 9. The random number generator gathers environmental. Dec 29, 2015  If you run 'make load' or reboot, the kernel module will be loaded into the running kernel, but now will replace the /dev/urandom device file. The old /dev/urandom device is renamed (keeping it's inode number). This allows any running process that had /dev/urandom to continue running without issues. If your system has a means to generate random numbers involving not only a software algorithm (like the /dev/urandom devices in Unix), then:. Show how to obtain a random 32-bit number from that mechanism. You can use od to get numbers out of /dev/random and /dev/urandom. For example, 2 byte unsigned decimal integers, $ od -vAn -N2 -tu2 dev/urandom 24352 1 byte signed decimal integer, $ od -vAn -N1 -td1 dev/urandom -78 4 byte unsigned decimal integers, $ od -vAn -N4 -tu4 dev/urandom man od for more information on od.

P: n/a
In the following piece of code, which simply generates a sequence of
(random) octal codes, I'm surprised by the apparent non-randomness of
/dev/random. It's not noticeable unless RAND_LENGTH is largish. I was
under the assumption that /dev/random was 'more random' than
/dev/urandom, and that it would block if it ran out of entropy until it
got more. Why am I seeing so many zeroes in my output?
#include <stdio.h>
#include <fcntl.h>
#define RAND_LEN 1024
void
read_random( const char* dev ) {
int i, fd;
char dat[RAND_LEN];
fd = open( dev, O_RDONLY );
dat[RAND_LEN] = '0';
if( fd != -1 ) {
read( fd, dat, RAND_LEN );
for( i = 0; i < RAND_LEN; i++ ) {
dat[i] = (dat[i] >> 4 & 0x07) + 48;
}
printf( '%s: %snn', dev, dat );
} else {
exit( 1 );
}
close( fd );
}
int
main( void ) {
read_random( '/dev/random' );
read_random( '/dev/urandom' );
return( 0 );
}
506$ ./test
/dev/random: 20005061706352643760251034665507247403176742630660 50462223206040017306150002434274350703035033674561 20754173510400040000000050000000000007737204577300 00177356040504450022043404000034041773610464046404 00000000000000000000000000000000000000000000000000 00000000000000000000000000640423461000000000000000 00000000000000000000000000002404000000004100700000 00634610000000000000000000000000000000000000000000 00000000000000000000000000005604000000000000340437 73040037730504300000004773000000000000000000000000 00003000100000000000000000000000000000000000000000 00000000000000000000000000000450045004000000002000 70041304330407040000170434041704050427730704050400 30160457732404000067040000000000000000000070042000 64040000340400006404677300045004000000005773200070 04130433040704000017043404640440004773070440000770 00007773240400005704000000000000000000000000000034 04710007047773220417046704000000000000777300000000 00000000077007735404050416046304070457733773020470 00200040044773577311046414641437736504641457733404 000054041773220464045704
/dev/urandom: 10313700276075133047145322754731744715330540305544 55772411741125544374737071744665152471472301655103 21673032612147044376361336471103425426601777564215 27537506506760532046755677545002343626131545501130 60140067534031123241466461750705230751645572440071 57744425536470274352332415164131435115125573101442 74556544717777054520152351764241666207571007700122 35623563012311717741547124617262165454244161061517 74201651063200446176135471662402411424412532245563 11545142476223664702172000553652612247511550424514 72612104741103553240132614710710775524572432011176 15642610621436346764640170271720054525337367306022 20367455521635765367573615753123615162510360064030 26113642124742630634422243216772330177360713406462 47534536645354770361405340770217451441530701353725 67322557767603402406511316575637667506305617702430 35222250564070154307150656704155003661646277201332 46523045641760343566266442731667313365016666076430 23673210310073545356647564170524251663066260134503 70701275067537603265673560312322526077022157223404 211323047413633213326054
--
Ron Peterson
Network & Systems Manager
Mount Holyoke College

Hi everyone and good morning :) .
i want to simply read from the linux file 'urandom' a random number and print it out on screen.just simple as that.
this function should be in a file called myrandom.c ( myrandom.h must be made also, which has my function dekleration ) . i will have to compile it later to a static libray and to dynamic library, and then write a main program which prints out 5 random numbers using the static library .
and another main program which prints out 5 random numbers using the dynamic library.
i wrote the myrandom.c code and myrandom.h code i dont know if they are correct .
i tested myrandom.c inside a main program and it gives me random number , but its very big .
ist that the right way to grap a random number from the urandom file?
many thanks

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Dev Urandom Example C V

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You're also using printf incorrectly. When you are printing out the value of an int, printf does not want the address of that int. It wants the int itself.

printf('%d', &rNumber); is wrong.
printf('%d', rNumber); is right.

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WTF is going on with this?

Urandom Warning

It's still wrong. str is effectively an int*, so &str is an int**, so *(&str) is an int*. So you're doing exactly what you were doing before (wrongly providing an int* when you …

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Dev urandom example c code

/dev/urandom C++

sepp2k378

Dev Urandom Example C

You need to #include <stdio.h> to get the declaration of fopen. As it is now you're implicitly declaring fopen in a way that is incompatible with its definition. You should be getting a warning about that (and in C99 and later you should instead be getting an error that you're using a function without a declaration).

Once you do that, you should be getting another warning that you're implicitly converting the result of fopen from FILE* to int. That's because fopen doesn't read anything from the file nor does it return an int. fopen opens the file and then returns a file pointer. That file pointer can then be given to other file IO functions (like fread, fwrite, fgets, fscanf, fprintf etc.), which will actually read from or write to the file. Once you're done working with the file, you need to close it by passing the file pointer to fclose.

So no, you're not currently doing it correctly. The number you're printing is simply the numeric value of whichever pointer was returned by fopen. It has nothing to do with the contents of the file.

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