Thread: C Warning message

I have the following c function that returns a random number between 0 and maxR.

Code:

#include <stdio.h>
char LB_Random(char *maxR,char *dummy)
	{	
	int i;
	static char n[10];
	int rMax = (int)maxR;	
	rMax++;
	srand(time(NULL));
	i = rand() % rMax;
	strcpy(n,(char*)i);
	return n;	
	}

When I compile it it points the return line giving this warning message:

warning C4047: 'return' : 'unsigned char ' differs in levels of indirection from 'unsigned char [10]'

Should I be worried?

Yes you should be worried.

You return n, an array, which differs in indirection from an unsigned char, the apparent type of the function's return value.

I'm also uncomfortable with the fact that you could end up calling srand more than once if you use this function more than once. There is also an awful lot of casting magic going on. You need to learn how to convert strings and numbers interchangeably in C.

Well the string maxR get's passed in from an external program, but it will be a number. So that's why I need to convert it back to an integer so that I can use it in my calculations. What would be the proper way of doing this?

The way I understood srand was that i generated a seed for rand, so if the seed is the same every time, you'll get the same random number out, hence why i'm using the system time as the seed, as it shall be different every time it get's called.

It's been a while since i've done C programming, what would be the correct way of declaring the function. I have to use a static char array as the memory being used by the return parameter is not being automatically released. So I have to return this value.

If those functions are not in that header file, how does it compile in the first place?

Perhaps give me an example of how you would re-structure this code?

> The way I understood srand was that i generated a seed for rand.
This is right, and then the rest of what you type is a result of a misunderstanding. Pseudorandom number generators like the one in rand only need to be seeded once and only once to set off an arithmetic series. This series produces "random" numbers over a period of time, after which the series repeats. There's really not much you can do about the latter part except implement something with a better period if it's not random enough.

If you want to return a static array, that's fine, just be aware that you are returning a pointer to char, and not a char. The pointer which you return points to the first element in the array.

> If those functions are not in that header file, how does it compile in the first place?
Your compiler warnings must not be set high enough. There should be options available to change this somewhere.

A more correct demonstration to convert numbers and strings was linked to in my previous post.

Originally Posted by vart

so the function is called like this:

Code:

int a = 10;
LB_Random((char*)&a,NULL)?

or like this:
LB_Random("10",NULL);


So in general - instead of using random generator - you are using seed generator based on time. Noone said it will be a good distribution. Seed is used once per program - then only rand is called...

Called like the second one.

Sorry i'm not sure what you're saying here. Is the seed not used for rand?

Ok slowly but surely . Here's what i've got now

Code:

#include <stdlib.h>
char LB_Random(char *maxR,char *dummy)
	{	
	int i;
	static char n[10];
	int rMax = atoi(maxR);	
	rMax++;
	i = rand() % rMax;
	sprintf(n,"%d",i)
	return n;	
	}

I'm still conscious on how I define my function in the first place, i.e. i'm return a char where as I want to return a static char array, how do I do this in C?