axes_objects/contourc.cpp:584: out-of-bounds while accessing the _Z_rows[n_col][n_row] in contours::is_lower_level()

[leha-bot]

Bug category

• bug - compilation error
• bug - compilation warning
• bug - runtime error
• bug - runtime warning
• bug - logic error

Describe the bug
At some grids (e.g. transposed) the matplot::contourf() fails with runtime error.

Steps to Reproduce

1. This error could be triggered by simply swapping X and Y in examples/contour_plots/contourf/contourf_1.cpp

# Your steps go here
mkdir build
cd build
cmake ..  -DCMAKE_BUILD_TYPE=Debug

Output

# The output you got
/usr/include/c++/9/bits/stl_vector.h:1042: std::vector<_Tp, _Alloc>::reference std::vector<_Tp, _Alloc>::operator[](std::vector<_Tp, _Alloc>::size_type) [with _Tp = std::vector<double>; _Alloc = std::allocator<std::vector<double> >; std::vector<_Tp, _Alloc>::reference = std::vector<double>&; std::vector<_Tp, _Alloc>::size_type = long unsigned int]: Assertion '__builtin_expect(__n < this->size(), true)' failed.

Platform

• cross-platform issue - linux
• cross-platform issue - windows
• cross-platform issue - macos

Environment Details:

• OS: CentOS
• OS Version: 8
• Compiler: GCC
• Compiler version: 9.3.1

Additional context

While debugging I found that sometimes the std::find_if() here returns end iterator and at next lines the variables n_row, n_column are could not be adjusted and this is follows to out-of-bounds error in header.
The dirty hack is the simply decrement n_row, n_col after checking all directions and before determining the opposite points here, but I doubt in robustness of this fix. @alandefreitas what do you think?

[alandefreitas]

This is fixed, right?

[leha-bot]

Unfortunately no, we should decide how to deal with

matplotplusplus/source/matplot/axes_objects/contours.cpp

Lines 540 to 545 in 7b3c042

	auto it_y =
	std::find_if(Y_data_.begin(), Y_data_.end(),
	[&](const auto &y_row) { return y_row[0] > avg_y; });
	auto it_x = std::find_if(
	X_data_[0].begin(), X_data_[0].end(),
	[&](const double &x_row_value) { return x_row_value > avg_x; });

if std::find_if returns end iterator, as my supposed fix in issue description for this place is not good and robust;

[alandefreitas]

OK. I'll have a look at that.