Error random was not declared in this scope

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Тема: random() в Си. Где он?  (Прочитано 4523 раз)

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• General C++ Programming
• <random> not working?

<random> not working?

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void DisplaySix(unsigned char iNumber)
{
  unsigned int iDisplay;
  default_random_engine engine;
  uniform_int_distribution<int>distribution(1,6);
  do
  {
    iDisplay=distribution(engine);
    cout << iDisplay;
    cout << "n";
    iNumber--;
  }
  while(iNumber>0);
  return;
}

In function 'void DisplaySix(unsigned char)':
error: 'default_random_engine' was not declared in this scope
error: expected ';' before 'engine'
error: 'uniform_int_distribution' was not declared in this scope
error: expected primary-expression before 'int'
error: expected ';' before 'int'
error: 'engine' was not declared in this scope
error: 'distribution' was not declared in this scope

error: 'default_random_engine' is not a member of 'std'
error: 'uniform_int_distribution' is not a member of 'std'

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• [SOLVED] Codeblocks,C++, rand() was not declared.

1. Codeblocks,C++, rand() was not declared.
   

   Hopefully i posted this in the right area (sorry if i didnt).
   Hey there. Learning C++ from C++ For Dummies All-In-One Second edition where they teach it with Codeblocks (the reason why i bought it).

   Ok, my problem is basically I get an error as such when building:

   Code:

   error; 'rand' was not declared in this scope

   Here’s my sourcode (slightly modified from the books version. Just added a prototype for the function).
   rand() is located in the GetSecretCode() function

   Code:

   #include <iostream>
   #include <sstream>
   
   using namespace std;
   
   string *GetSecretCode();
   
   int main()
   {
       string *newcode;
       int index;
   
       for ( index = 0; index < 10; index++ )
       {
           newcode = GetSecretCode();
           cout << newcode << endl;
       }
   
       cout << "All done here" << endl;
   
       return 0;
   }
   
   string *GetSecretCode()
   {
       string *code = new string;
       code->append("CR");
   
       int randomnumber = rand();
       ostringstream converter;
       converter << randomnumber;
   
       code->append(converter.str());
       code->append("NQ");
   
       return code;
   }

   What am I missing code wise?
   something I didn’t «#include» ?

   ---

2. Re: Codeblocks,C++, rand() was not declared.
   

   rand is defined in cstdlib (there is no standard c++ random function yet). so include:
   #include <cstdlib>

   also you have memory leaks in your code as you don’t delete the created string
   generally you should avoid dynamically allocating stuff where it is not needed.
   you can rewrite it to something like this:

   Code:

   // very long string which might be expensive to copy, so use a reference
   void createCopyExpensiveString(string & str) {
   // dostuff
   }
   
   // short string, cheap to copy
   string createShortString()
   {
      return "shortstring";
   }
   
   void main()
   {
     string str;
     createCopyExpensiveString(str);
     cout << str << endl;
     string str2 = createShortString();
     cout << str2 << endl;
   } // str and str2 go out of scope here and get deleted automatically

   Last edited by MadCow108; October 6th, 2009 at 03:35 PM.

   ---

3. Re: Codeblocks,C++, rand() was not declared.
   

   Hey thanks, it worked off the bat.

   Just out of curiosity I tried it on Vista as well but without cstdlib
   and it works…..whats with that?

   It’s obvious now that although they promote crossplatform code in this For Dummies book, they only tested the code on Winduhs…

   For shame..
   Any idea why it works differently?

   ---

4. Re: Codeblocks,C++, rand() was not declared.
   

   It is a usual phenomenon…

   Many compilers include some «hidden» libraries that support the underlying operating system. For example, in Vista, your compiler may add <cstdlib> subtlely.

   Another example is GCC’s linker in Linux that automatically adds «stdlib.h» by default, without prior declaration by the programmer.

   I hope I made it clear for you.

   Happy coding!

   ---

5. Re: Codeblocks,C++, rand() was not declared.
   

   Thanks guys.
   that was the case with C when I learned it earlier this year..
   MadCow, I shall ponder upon your unique(odd?) code and when I have better grasped C++ then maybe I shall better understand it.
   Toodles~

   

   ---

6. Re: Codeblocks,C++, rand() was not declared.
   

   Originally Posted by myromance123
   

   Thanks guys.
   that was the case with C when I learned it earlier this year..
   MadCow, I shall ponder upon your unique(odd?) code and when I have better grasped C++ then maybe I shall better understand it.
   Toodles~

   

   MadCow’s code isn’t really odd. He makes a great point. A lot of people use a lot of pointers when they’re not really needed. It is important to really understand what pointers are for, and only use them when necessary because pointers can be the main source for memory leaks. If you don’t really need them, don’t use them.

   Today you are You, that is truer than true. There is no one alive who is Youer than You. — Dr. Seuss

   ---

7. Re: Codeblocks,C++, rand() was not declared.
   

   ok i new to programming and went i try to use the �rand� i get this was not declared in this scope|

   #include <iostream>
   #include <cmath>

   int main()
   {
   using namespace std;

   double num1;
   num1 = rand ();
   cout << num1 <<endl;

   return 0;
   }

   ---

8. Re: Codeblocks,C++, rand() was not declared.
   

   Originally Posted by foxgoooo
   

   ok i new to programming and went i try to use the ‘rand’ i get this was not declared in this scope
   …

   Probably because rand belongs to cstdlib, not cmath. Also, avoid resurrecting long forgotten threads.

   ---

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