c++ calling a class within a class -

so had following code ran perfectly. here "rngsource" makes instance of class contained in rand.h. rng.rfloat64() calls random numbers between 0 , 1.

main.cpp

#include "rand.h"   // rngsource  rngsource rng;  class particle{ public:     double r[nd], v[nd];     particle()     {             (int i=0; i<nd; ++i)             {                     r[i]=l*rng.rfloat64();                     v[i]=rng.rfloat64();              }      } }; 

but when tried separate class implementation main.cpp particle.h , particle.cpp, indicated below:

particle.h

#ifndef particle_h #define particle_h  class particle{  public:      double r[2], v[2];     particle(); };  #endif 

particle.cpp

#include "rand.h"    // rngsource #include "particle.h"  particle::particle() {     double ran = (double) rand()/(double)rand_max;     static const double l=10;     (int i=0; i<2; ++i)     {             r[i]=l*ran;             v[i]=ran;                 } } 

while new main.cpp looks this:

#include "rand.h"    /* rngsource() */ #include "particle.h"   /* particle class */  rngsource rng;  int main(){     rng.rseed(getpid()*time(null));     particle p[n];     .... } 

but when try compile following errors:

particle.cpp: in constructor ‘particle::particle()’: particle.cpp:20:17: error: ‘rng’ not declared in scope       r[i]=l*rng.rfloat64(); //ran;              ^ particle.o:(.data+0x0): multiple definition of `rng_cooked' new.o:(.data+0x0): first defined here particle.o:(.data+0x1300): multiple definition of `kn' new.o:(.data+0x1300): first defined here particle.o:(.data+0x1500): multiple definition of `wn' new.o:(.data+0x1500): first defined here particle.o:(.data+0x1700): multiple definition of `fn' new.o:(.data+0x1700): first defined here  new.cpp:(.text+0x1fb1): undefined reference `rngsource::rseed(long long)' particle.o: in function `particle::particle()': particle.cpp:(.text+0x1fa2): undefined reference `rngsource::rseed(long long)' particle.cpp:(.text+0x1fb5): undefined reference `rngsource::rfloat64()' particle.cpp:(.text+0x1fda): undefined reference `rngsource::rfloat64()' collect2: error: ld returned 1 exit status 

would here happen know how fix this? thank you.

three problems.

problem 1:

particle.cpp: in constructor ‘particle::particle()’: particle.cpp:20:17: error: ‘rng’ not declared in scope       r[i]=l*rng.rfloat64(); //ran; 

the ultra cheesy answer add extern rngsource rng; particle.cpp above particle constructor. extern means variable exists, storage allocated elsewhere. linker track down you. quick, dirty, , on road minimal code changes.

better solutions add extern rngsource rng; rand.h , define rngsource rng; in rand.cpp users or placing extern rngsource rng; in brand new main.h , include main.h in particle , other modules called main.

the best solution create bool init(rngsource & rng) function in particle , grunt work constructor's doing. way if rng doesn't exist, compiler catches when try call init.

particle p[n]; (size_t index; index < n; index++) {     p[index].init(rng); } 

problem 2

particle.o:(.data+0x0): multiple definition of `rng_cooked' new.o:(.data+0x0): first defined here particle.o:(.data+0x1300): multiple definition of `kn' new.o:(.data+0x1300): first defined here particle.o:(.data+0x1500): multiple definition of `wn' new.o:(.data+0x1500): first defined here particle.o:(.data+0x1700): multiple definition of `fn' new.o:(.data+0x1700): first defined here 

rng_cooked, kn, wn, , fn being defined in rand.h. means includes rand.h tries create own version of variables resulting in collisions when linker tries line names storage locations.

solution similar first problem: add extern variable definitions in rand.h , define them in rand.cpp.

problem 3

new.cpp:(.text+0x1fb1): undefined reference `rngsource::rseed(long long)' particle.o: in function `particle::particle()': particle.cpp:(.text+0x1fa2): undefined reference `rngsource::rseed(long long)' particle.cpp:(.text+0x1fb5): undefined reference `rngsource::rfloat64()' particle.cpp:(.text+0x1fda): undefined reference `rngsource::rfloat64()' 

no idea. passing rand.cpp gcc?