[GiNaC-devel] Archiving an empty container

[Vladimir V. Kisil]

	Dear All,

	There is an issue with GiNaC archiving an empty container. This
  is illustrated by the code included below. The archived empty list z
  is read in the expression z1 as a list with one element. Also such
  code can crashes id an empty container is archived first.

  The reason is in lines 215-216 of container.h: here GiNaC got
  first=last for both: empty containers and containers with one element.

  I propose the attached patch, which modifies the return value of
  archive_node::find_last() (called at line 216 of container.h) by 1.
  All other calls of archive_node::find_last() are revised to agree with
  the change.

  Best wishes,
  Vladimir
-- 
Vladimir V. Kisil                 http://www.maths.leeds.ac.uk/~kisilv/
  Book:     Geometry of Mobius Transformations     http://goo.gl/EaG2Vu
  Software: Geometry of cycles          http://moebinv.sourceforge.net/
  Jupyter (Colab):         https://github.com/vvkisil/MoebInv-notebooks
  Jupyter (CodeOcean):            http://doi.org/10.24433/CO.9934595.v2
======================================
#include <iostream>
#include <fstream>
#include <stdexcept>
#include <ginac/ginac.h>

using namespace std;
using namespace GiNaC;

int main(int argc, char** argv) {
	ex x = lst{1,2}, y = lst{3}, z = lst{};
	
	GiNaC::archive A;
	A.archive_ex(x, "2elem");
	A.archive_ex(y, "1elem");
	A.archive_ex(z, "empty");

	ofstream out("/tmp/test.gar", ios::binary);
	out << A;
	out.flush();
	out.close();

	GiNaC::archive A1;
	std::ifstream ifs("/tmp/test.gar", std::ifstream::in | ios::binary);

	ifs >> A1;
	
	ex x1 = A1.unarchive_ex(lst{}, "2elem")	;
	ex y1 = A1.unarchive_ex(lst{}, "1elem")	;
	ex z1 = A1.unarchive_ex(lst{}, "empty")	;

	x1.dbgprint(); // -> {1,2}
	y1.dbgprint(); // -> {3}
	z1.dbgprint(); // -> {1}

	return 0;
}

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