dvir schirman wrote:

Hi

I am using boost/random library in order to create a normal distributed noise. I want to call my my_class::noise() functions several times, but I want to initialize the generator only once. I tried to declare and initialize the generator at the constructor of my_class, but then my_class::noise() doesn't recognized the generator.

If you just want the generator to be initialized once for each object of my_class that is created, this will do the trick: class my_class { protected: typedef boost::mt19937 generator_type; typedef boost::normal_distribution<> normal_distribution_type; typedef boost::variate_generator normal_random_type; generator_type m_generator; normal_distribution_type m_normal_distribution; normal_random_type m_normal_random; public: my_class() : m_generator(42u), m_normal_distribution(5,10), m_normal_random(m_generator, m_normal_distribution) { ; // do nothing } double noise() { return m_normal_random(); } }; If you want the generator to be initialized only once total (no matter how many instances of the class are created), you can use this: class my_class_static { protected: typedef boost::mt19937 generator_type; typedef boost::normal_distribution<> normal_distribution_type; typedef boost::variate_generator normal_random_type; static generator_type m_generator; static normal_distribution_type m_normal_distribution; static normal_random_type m_normal_random; public: static double noise() { return m_normal_random(); } }; You never actually need an instance of the class my_class_static since the noise function is static. The static member m_generator will be initialized only once, at program startup. (Note that this is not thread-safe and would need to be protected with a lock.) David Testing code: static void Test_my_class() { my_class mine; for(unsigned int i=0 ; i<9 ; ++i) { double d = mine.noise(); std::cout << d << " "; } std::cout << std::endl; } static void Test_my_class_static() { for(unsigned int i=0 ; i<9 ; ++i) { double d = my_class_static::noise(); std::cout << d << " "; } std::cout << std::endl; } int main(int argc, char* argv[]) { std::cout << "Testing my_class - next two lines should be same\n"; Test_my_class(); Test_my_class(); std::cout << "Testing my_class_static - next line same as above, last line different\n"; Test_my_class_static(); Test_my_class_static(); return 0; }