体系结构x86_64 c++的未定义符号

我正试图在C++中创建一个自定义的"Matrix"类，但遇到了一个我无法理解的"架构x86_64的未定义符号："错误。我的相关代码是-

标题

#ifndef CORE_H
#define CORE_H
#include <stdint.h>
class Size
{
public:
    Size(const uint64_t nrows, const uint64_t ncols, const uint64_t nframes);
    uint64_t rows;
    uint64_t cols;
    uint64_t frames;
};
template <typename T>
class Matrix
{
public:
    Matrix(const uint64_t rows, const uint64_t cols, const uint64_t frames);
    Matrix(const uint64_t rows, const uint64_t cols, const uint64_t frames, T *data);
    void print();
private:
    Size sz;
    T *_data;
};
#endif //CORE_H

来源

#include <string.h>
#include <cstdlib>
#include <stdio.h>
#include "core.h"
Size::Size(const uint64_t nrows, const uint64_t ncols, const uint64_t nframes)
{
    rows = nrows;
    cols = ncols;
    frames = nframes;
}
template <typename T>
Matrix<T>::Matrix(const uint64_t rows, const uint64_t cols, const uint64_t frames)
{
    Matrix<T>(rows, cols, frames, malloc(rows * cols * frames * sizeof(T)));
}
template <typename T>
Matrix<T>::Matrix(const uint64_t rows, const uint64_t cols, const uint64_t frames, T *data)
{
    sz = Size(rows, cols, frames);
    _data = data;
}
template <typename T>
void Matrix<T>::print()
{
    printf("[");
    for (uint64_t f = 0; f < sz.frames; f++) {
        printf("[");
        for (uint64_t r = 0; r < sz.rows; r++) {
            for (uint64_t c = 0; c < sz.cols; c++) {
                printf("%.3f,", element(r, c, f));
            }
            printf("n");
        }
        printf("]n");
    }
    printf("]n");
}

测试

#include "core.h"
int main(int argc, char *argv[])
{
    int data[] = { 1, 2, 3, 4, 5, 6, 7, 8};
    Matrix<int> mat(2, 2, 2, data);
    mat.print();
    return 0;
}

错误

Undefined symbols for architecture x86_64:
  "Matrix<int>::print()", referenced from:
      _main in rand.cpp.o
  "Matrix<int>::Matrix(int, int, int, int*)", referenced from:
      _main in rand.cpp.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make[2]: *** [examples/rand] Error 1
make[1]: *** [examples/CMakeFiles/rand.dir/all] Error 2
make: *** [all] Error 2

我确信这是件小事，但我想不通。任何帮助都将不胜感激！