(C++) _algo.c: Call to undefined function 'rand'

 

Compile error.

 

 

 

 

Full error message

 

---

[C++ Error] _algo.c(432): E2268 Call to undefined function 'rand'

 

This takes you to the following code in _algo.c:

 

---

// Return a random number in the range [0, __n). This function encapsulates // whether we're using rand (part of the standard C library) or lrand48 // (not standard, but a much better choice whenever it's available). template <class _Distance> inline _Distance __random_number(_Distance __n) { #ifdef _STLP_NO_DRAND48   return rand() % __n; //THIS LINE #else   return lrand48() % __n; #endif }

 

 

 

 

Cause

 

IDE: C++ Builder 6.0

Compiler: Borland BCC32.EXE version 6.0.10.157

Project type: Console Application

 

The compiler cannot find the function rand (note that it does not complain that it cannot find std::rand). But it will only need rand when making use of the function above. For example, when you use std::random_shuffle.

 

---

#include <algorithm> #include <vector> int main() {   std::vector<int> v;   std::random_shuffle(v.begin(),v.end()); }

 

 

 

 

 

Solution

 

It is not a good idea to modify standard header files. But the compiler cannot find rand, but it can find std::rand. So I add the namespace std to rand. And I have never had trouble with this.

 

---

// Return a random number in the range [0, __n). This function encapsulates // whether we're using rand (part of the standard C library) or lrand48 // (not standard, but a much better choice whenever it's available).   template <class _Distance> inline _Distance __random_number(_Distance __n) { #ifdef _STLP_NO_DRAND48   return std::rand() % __n; //THIS LINE #else   return lrand48() % __n; #endif }