Create random number with exponential distribution in c++ (visual stduio) -

i trying create random number exponential distribution. when tested simple example, worked well. when create in project, not work. project include many classes different objects. class in project:

user.h:

#include<iostream> #include<queue> #include<math.h> #include<random> #include"packet.h" using namespace std;  class user { protected:     queue<packet*> packetlist;     const double rnd = 1.0 / 100;     std::default_random_engine generator;     exponential_distribution<> packetarrivalrate(double); // error if "packetarrivalrate(1.0/100)" public:     void newpacket(); }; 

user.cpp:

#include"user.h";  exponential_distribution<> user::packetarrivalrate(double) {     return exponential_distribution<>(rnd); }  void user::newpacket() {     packet* p = new packet;     packetlist.push(p);     double time = packetarrivalrate(generator); //this line error } 

can me create "time" exponentially distributed random number.

the problem calling packetarrivalrate generatorare parameter, when function expects double. said function return exponential_distribution<> needs generator give exponentially distributed numbers.

one simple (and ugly) way solve give packetarrivalrate proper argument (note argument ignored function, value doesn't matter), , call operator() on return value:

double time = packetarrivalrate(0)(generator); 

alternative design

a more reasonable way not ignore argument, , provide rnd:

double time = packetarrivalrate(rnd)(generator); 

and define packetarrivalrate this:

exponential_distribution<> user::packetarrivalrate(double lambda) {     return exponential_distribution<>(lambda); } 

random engines

please use mersenne twister pseudo-random generator (std::mt19937 or std::mt19937_64) instead of std::default_random_engine. may provide better random numbers. see this video author of <random>.