What can cause LNK2019 error in VisualStudio? - c++

Question

I have created a simple cpp project in Visual Studio, but have encountered the follwoing linking error:
LNK2019: unresolved external symbol "public: class std::vector > __thiscall solver::euler(class point_3d (__cdecl*)(class point_3d,double),double,int,class point_3d,double)" (?euler#?$solver#Vpoint_3d####QAE?AV?$vector#Vpoint_3d##V?$allocator#Vpoint_3d###std###std##P6A?AVpoint_3d##V4#N#ZNH0N#Z
I have no idea what may be causing this and would be gratefull for any advice.
Files that constitute the project:
main.cpp
#include "point_3d.h"
#include "solver.h"
point_3d lorentz(point_3d val, double t) {
double x = 10*(val.get_y()-val.get_x());
double y = val.get_x()*(28.0- val.get_z())- val.get_y();
double z = val.get_x()* val.get_y()-(8.0/3)* val.get_z();
return point_3d(x, y, z);
}
int main(){
auto file = std::ofstream("data/results.json");
solver<point_3d> sol;
std::vector<point_3d> result = sol.euler(lorentz, 0.01, 50000, point_3d(1, 1, 1));
}
solver.h
template<typename T>
class solver{
public:
std::vector<T> euler(T (*f)(T val, double s),double h, int steps, T val, double t0 = 0.0);
std::vector<T> back_euler(T (*f)(T val, double s), double h, int steps, T val, double t0 = 0.0,int n=50);
std::vector<T> rk_2(T (*f)(T val, double s), double h, int steps, T val, double t0 = 0.0);
std::vector<T> rk_4(T (*f)(T val, double s), double h, int steps, T val, double t0 = 0.0);
};
solver.cpp
#include "solver.h"
template<typename T>
std::vector<T> solver<T>::euler(T (*f)(T val, double s), double h, int steps, T val, double t0 ) {
std::vector<T>res;
res.resize(steps + 1);
res[0] = val;
double t = t0;
for (int i = 0; i < steps;i++) {
res[i + 1] = res[i] + h * f(res[i], t);
t += h;
}
return res;
}
template<typename T>
std::vector<T> solver<T>::back_euler(T (*f)(T val, double s), double h, int steps, T val, double t0, int n) {
std::vector<T>res;
res.resize(steps + 1);
res[0] = val;
double t = t0;
for (int i = 0; i < steps; i++) {
t += h;
res[i + 1] = res[i];
for (int j = 0; j < n; j++) {
res[i + 1] += res[i] + h * f(res[i + 1],t);
}
}
return res;
}
template<typename T>
std::vector<T> solver<T>::rk_2(T (*f)(T val, double s), double h, int steps, T val, double t0) {
std::vector<T>res;
res.resize(steps + 1);
res[0] = val;
double t = t0;
for (int i = 0; i < steps; i++) {
auto k = h * f(res[i], t) / 2.0;
res[i + 1] = res[i] + h * f(k+res[i],t+h/2.0);
t += h;
}
return res;
}
template<typename T>
std::vector<T> solver<T>::rk_4(T (*f)(T val, double s), double h, int steps, T val, double t0) {
std::vector<T>res;
res.resize(steps + 1);
res[0] = val;
double t = t0;
for (int i = 0; i < steps; i++) {
auto k1 = f(res[i],t);
auto k2 = f(res[i]+h/2.0*k1, t+h/3.0);
auto k3 = f(res[i] + h / 2.0 * k2, t + 2*h / 3.0);
auto k4 = f(res[i] + h * k3, t + h);
res[i + 1] = res[i] + (k1 / 6 + k2 / 3 + k3 / 3 + k4 / 6) * h;
t += h;
}
return res;
}
point_3d.h
class point_3d{
double x;
double y;
double z;
public:
point_3d(double x, double y, double z): x(x), y(y), z(z) {};
double get_x();
double get_y();
double get_z();
point_3d operator+(point_3d other);
point_3d& operator=(point_3d other);
friend point_3d operator*(double k, point_3d p);
};
point_3d.cpp
#include "point_3d.h"
double point_3d::get_x() {
return x;
}
double point_3d::get_y() {
return y;
}
double point_3d::get_z() {
return z;
}
point_3d point_3d::operator+(point_3d other) {
double x = get_x() + other.get_x();
double y = get_y() + other.get_y();
double z = get_z() + other.get_z();
return point_3d(x, y, z);
}
point_3d& point_3d::operator=(point_3d other) {
this->x = other.get_x();
this->y = other.get_y();
this->z = other.get_z();
return *this;
}
point_3d operator*(double k, point_3d p) {
double x = p.get_x();
double y = p.get_y();
double z = p.get_z();
return point_3d(k * x, k * y, k * z);
}

Answer 1

You need to include vector library to use std::vector.
#include <vector>
"Unresolved symbol" means that there is a class or a function declared but not found anywhere in the project (or in the libraries it includes).