I don't need to include <cstdlib> to call rand() function?

hey all, been a while (damn jobs)

so im familiar with the rand() function, and how to get a random number within a certain range, but as i was flipping through one of my books i noticed its telling me that i need to include <cstdlib> in order to call the rand() function.. however I ran the following code without it and got the same (random) results...

im just curious about how this is happening. Is it simply good practice to include <cstdlib> or was there some kind of C++ update that allows the rand() function to be called without it? not of uttermost importance, just curious

Code:

#include<iostream>
#include <ctime>


using namespace std;


int main()
{

 srand(time(0));
 
 for (int i = 0; i < 15; i++)
      {
       int randomNumber= (rand() % 6) + 1;
 
       cout<< randomNumber << endl;
       }
 system("pause");
}

this code runs fine for me and still generates random numbers from 1 - 6...

It is not simply good practice. The code will not compile for me.

main.cpp:11: error: 'srand' was not declared in this scope
main.cpp:15: error: 'rand' was not declared in this scope
main.cpp:19: error: 'system' was not declared in this scope
Process terminated with status 1 (0 minutes, 0 seconds)
3 errors, 0 warnings

What we can learn from this is that you always need to include the headers so that the types and functions you want to use are made ready. You are simply lucky that your implementation of the libraries include at some point the missing headers in your source code for you. You cannot depend on this, by way of my example.

Well the code runs fine at me too.However i checked the ref and i saw that <cstdlib> is needed for RAND_MAX,not for rand().Check for yourselves rand - C++ Reference

Originally Posted by std10093

Check for yourselves rand - C++ Reference

What are you saying ?. This link clearly tells that <cstdlib> has to be included for int rand( void ). Look at the top right.

Kurt

While what Zuk said is true,at the same link,at their own example,they do not use it .

That's because this example is C-code and they do #include <stdlib.h>

Kurt

Having C code in a C++ site <--Genius So tell us Zuk,why did not the compiler complained?Neither to me or to Mike? I can not figure out

In C, rand() does not strictly require <stdlib.h> to be #include'd, since the compiler assumes an int return type and int arguments by default. This is, however, considered very poor technique.

In C++, the using rand() without the appropriate header file is illegal. In practice, however, it depends on the implementation, since other header files sometimes #include <cstdlib> or <stdlib.h>. The problem that brings is that the C++ standard does not require standard headers to #include each other, so code which relies on it can break when taken to other compilers (or when a compiler/library is upgraded and the code is recompiled).

Originally Posted by std10093

Having C code in a C++ site <--Genius

<stdlib.h> is in the C++ standard library too, but with small differences from <cstdlib>, and is deprecated.

Originally Posted by laserlight

<stdlib.h> is in the C++ standard library too, but with small differences from <cstdlib>, and is deprecated.

As <stdio.h> but i do not think that C++ developers use printf instead of cout.