I do have a function in C to give me a unsigned short random number from 0 to 65535.
How can I make it to give me a greater number without much calculating? (r * 65536 + r)

I've made a function in C to do that for me:

static unsigned long convert_random_to_long()
static unsigned char row[4];
static unsigned short *p1=&row[0];
static unsigned short *p2=&row[2];
static unsigned long *long_random=&row[0];


return *long_random;

It gave me a few warnings but worked well.
In C++ it is not giving anymore warnings, simply ends up in errors because of the strict type checking.

How could I make my function work in C++?

Thank you in advance,

Deleted Member

Unfortunately I cannot edit my post.
Please read line 9 as *p2=random();

In C++, you need to do the cast explicitly:

static unsigned char row[4];
static unsigned short *p1 = reinterpret_cast<unsigned short *>(&row[0]);
static unsigned short *p2 = reinterpret_cast<unsigned short *>(&row[2]);
static unsigned long *long_random = reinterpret_cast<unsigned long *>(&row[0]);

That should solve your problem.


You must explicitly inform your C++ compiler that you wish to convert the short pointer type to a long pointer type.

static unsigned long* long_random = (static unsigned long*) row;//make row an array of 2 shorts

I don't think you need a character array here. Just use two shorts. And are you sure you want to use static here?

Alternately, you could just do this:

unsigned long value;
value = rand();
value = (value<<16)|rand();

How this works is simple. After value = rand() might have something in binary that looks like this...note I didn't count the digits lol just assume it's 32 bits:
0000000000000000000001010101010101010101010 or some such, where the 2nd half is your random number.
now when you do value<<16, you left shift all that shit, so you now have

then, you combine that with another random number using the | character, which stands for OR, so you have, for example

1010101010101010101010000000000000000000000  //value<<16
0000000000000000000001111111101010110111111  //rand()
Thank you it's working!

Thank you very much guys, problem solved.
Mike was spot on!


cout << *long_random;

The result is: 65537 which is absolutely corrrrrect. (1*65536+1)

Great team here!!!

With the help of this I can generate even larger random numbers without the headaches of calculations.

Thinking about Greywolf's suggestion...

Edited 4 Years Ago by misi

Just use two shorts.

Good idea,thank you.

And are you sure you want to use static here?

Yes, I want to use static because this way the machine has to calculate the addresses only once while the program is running.

At Greywolf:

And are you sure you want to use static here?

Checking the code again I found that what you meant with that static.
No,I did not want that.Thank you.
The function is now : unsigned long convert_random_to_long()

unsigned long long convert_random_to_long_long()


cout << *long_long_random << "\n";

cout << *long_long_random << "\n";

The result of the test:


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