CODEWITHSUNDEEP
c++
quant
quant

Reputation: 23082

undefined reference to std random generator type

My program uses a Random class which manages a generator type and provides templated functions to return distributions using the given generator. However, when I compile it I invariably get undefined reference errors.

To illustrate the problem I've created a simple program which contains a Random class that simply provides a templated function Random::f() which returns a normally distributed number:

#include <random>                                                               
#include <iostream>                                                             

class Random                                                                    
{                                                                               
public:                                                                         
    template <typename T>                                                       
    static T f()                                                                
    {                                                                              
        std::normal_distribution<T> distribution(0,1);                             
        return distribution(generator);                                            
    }                                                                              

    static std::default_random_engine generator;                                   
};                                                                                 

int main()                                                                      
{                                                                               
    std::cout << Random::f<double>();                                           
    return 0;                                                                   
}

When I compile this using gcc 4.9.2 I get:

quant@900AX:~/Documents$ echo $CC
/usr/bin/gcc-4.9
quant@900AX:~/Documents$ $CXX -std=c++11 main.cpp 
/tmp/ccWCPiN7.o: In function `double Random::f<double>()':
main.cpp:(.text._ZN6Random1fIdEET_v[_ZN6Random1fIdEET_v]+0x2b): undefined reference to `Random::generator'
collect2: error: ld returned 1 exit status

Why am I getting this error?

Upvotes: 1

Views: 967

Answers (2)

masoud
masoud

Reputation: 56479

Put the definition out of the class:

std::default_random_engine Random::generator;

The code you have written, just declares the member object, you have to write a definition for it.

Upvotes: 4

P0W
P0W

Reputation: 47794

Static data members declarations in the class declaration are not definition of them.

Provide a definition to generator as its a static variable.

std::default_random_engine Random::generator = std::default_random_engine();

Upvotes: 3

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