Some nitpicking, more nitpicking.

[nyx-4]

0. https://stackoverflow.blog/2017/06/15/developers-use-spaces-make-money-use-tabs/, use spaces instead of tabs.

dstruct/slist.cpp

Line 1 in c9027c5

#include "node.h"

1. one does not simple use "node.h" without uploading it to GitHub
2. use .hpp or .hxx to explicitly state that this is C++ only header file, .h means its C compatible header which it's not (you're using templates)

dstruct/slist.cpp

Line 14 in c9027c5

int size = 0;

3. datatype should be size_t, you don't want negatives there (make it unsigned long long)

dstruct/slist.cpp

Lines 13 to 18 in c9027c5

	SNode<T>* tptr = head();
	int size = 0;
	while(tptr) {
	size++;
	tptr = tptr->nptr();
	}

4. iter is more standard than tptr in STL

dstruct/slist.cpp

Lines 32 to 33 in c9027c5

	if(head()) throw std::underflow_error("Can't get front value. List is empty");
	return head()->val();

5. Can i use GIF's in GH issuse.

dstruct/slist.cpp

Lines 37 to 39 in c9027c5

	SNode<T>* tptr = head();
	while(tptr->nptr()) tptr->nptr(tptr->nptr);
	return tptr->val();

6. Explain, what's going on here?

dstruct/slist.cpp

Line 46 in c9027c5

if(idx == 0 || !head()) {

7. idx == 0 || !head() is same as idx == 0 or empty() (more easy to understand)

dstruct/slist.cpp

Line 50 in c9027c5

else if (idx > 0) {

8. Make it size_t, and stop worrying about negative values.

dstruct/slist.cpp

Line 54 in c9027c5

while(idx_count < idx - 1 && tptr) {

9. Always check pointers first, and then any other condition, it'll save an head-ache later.

dstruct/slist.cpp

Line 64 in c9027c5

delete new_node;

10. Really, why made it in the first place?

dstruct/slist.cpp

Line 70 in c9027c5

if(idx < 0) throw std::invalid_argument("index value should be in range [0, size of list]");

11. But you didn't check for second condition, that is size of list, confusing...

dstruct/slist.cpp

Line 84 in c9027c5

while(idx_count < idx - 1 && tptr->nptr()) {

12. simplify the logic here,

[nyx-4]

I didn't know that @kazurem can write this convoluted code. Do not repeat this in project!

Edit: Also, no need to correct these issues.