How to view files over SSH using SimpleHTTPServer

It is convenient to connect to a remote computer using SSH and work at the shell. But viewing images files and other such common files can be a problem. Using a X server might not always be possible. A simple solution that works for me is to use the SimpleHTTPServer module that ships in Python.

Change to the directory which holds the files you want to view from a remote computer.
Run the SimpleHTTPServer there and provide a port number for the server:

$ python -m SimpleHTTPServer 8901

On the local computer, open a browser and connect to the server using the address: http://put-remote-computer-ip-here:8901
You can now view image files and other common file types right in the browser.

Tried with: Ubuntu 18.04

Floating point rounding modes in C++11

The standard C library has 4 floating point rounding modes available through cfenv.h. These are now available in C++11 through the header file cfenv.

The 4 floating point rounding modes are:

FE_TONEAREST
FE_DOWNWARD
FE_UPWARD
FE_TOWARDZERO

FE_TONEAREST rounds to the nearest integer. If the floating point value is exactly midway between two integers, then it does round half to even. The rest of the rounding modes are self explanatory.
None of the 4 rounding modes is equivalent to the round half away from zero which the round method does.
Anything to do with floating point operations is dependent on the FPU of the processor. So, the availability of these rounding modes and their values are highly dependent on the FPU of your processor.
On my x86_64 computer, all the 4 rounding modes were available and the values of these rounding modes were found to be:

#define FE_TONEAREST 0x000
#define FE_DOWNWARD 0x400
#define FE_UPWARD 0x800
#define FE_TOWARDZERO 0xC00

The FPU of your processor may support many other rounding modes in addition to these 4 modes.
On my x86_64 computer, I found that FE_TONEAREST was the default rounding mode when I used methods like rint and nearbyint to perform rounding.

How to use vimdiff

Vim can be used as a diff and merge tool. While it cannot match the beauty and power of GUI programs like Meld, it is immensely useful to diff and merge over a SSH session.

Vim can be invoked in diff mode either using vim -d or as vimdiff. Just pass in the names of the files to compare:

$ vimdiff 1.cpp 2.cpp
$ vim -d 1.cpp 2.cpp 3.cpp

Vim in diff mode displays each file in its own window side-by-side showing the diff sections in colors. You can switch between the windows using the normal Vim commands. (I use Ctrl-W-W.) And when you scroll down all the windows scroll down with you because they are locked to each other.
To switch to and fro between diffs use the ]-c and [-c commands.
To put the diff the cursor is resting on to the next window use the command dp
To pull the diff from the next window use the command do

Tried with: Vim 7.4 and Ubuntu 16.04

How to get the C++ standard

The C++ standard is the definitive source for the language. The official standards can be obtained from ISO for a fee. But the draft standard at any point of time can be compiled from its LaTeX source to PDF for free. Here is how:

Install these LaTeX packages:

$ sudo apt-get install latexmk texlive-latex-recommended texlive-latex-extra texlive-fonts-recommended

Clone the C++ draft standard repository:

$ git clone git@github.com:cplusplus/draft.git

Build a PDF of the standard:

$ cd source
$ latexmk -pdf std

If there are too many warnings, you might need to run the above command a second time. The result is a PDF of the C++ standard!

How to get function name in C++

Being able to access and print the function name from any location inside a C++ function can be useful for investigating programs.

There seems to be 3 different function name strings available:

__func__ is a constant that only holds the name of the function. It is part of the C and C++ standards.

int A::foobar(const std::vector<float>& fvec, bool isDragon)
{
    std::cout << __func__ << std::endl;
    // Output: foobar
}

__FUNCTION__ is a GCC constant whose output is exactly the same as __func__.
__PRETTY_FUNCTION__ is a GCC constant that is more useful for C++, because it holds the entire function signature:

int A::foobar(const std::vector<float>& fvec, bool isDragon)
{
    std::cout << __func__ << std::endl;
    // Output: int A::foobar(const std::vector<float>&, bool)
}

Reference: GCC: Function names as strings

How to round half to even

The round function available in C and C++ uses the rounding mode called round half away from zero. In this mode, the floating point value is rounded to the nearest integer value. When the floating point value is exactly midway, then the integer value away from zero is picked.

Many applications require the rounding mode to be round half to even. In this mode, when the floating point value is midway, the integer value that is even is chosen.

If you need round half to even, then you use the nearbyint or rint methods and set the rounding mode to FE_TONEAREST before you use them. For more information on these rounding modes, see this post.

#include <cfenv>
#include <cmath>
std::fesetround(FE_TONEAREST); // This is the default rounding mode for std::nearbyint
std::nearbyint(3.5f); // Result is 4
std::nearbyint(4.5f); // Result is 4

FE_TONEAREST is the default rounding mode, so you do not need to actually set it. Unless you believe it was set to some other rounding mode earlier in your code.

If you wish to do this rounding manually, then here is one possible implementation with test code:

How to find version of CUDA

Users of CUDA usually know its major.minor version.

If you want to know the full major.minor.patch version of CUDA you are using:

$ cat /usr/local/cuda/version.txt

For example, when I tried on my CUDA 9.2 installation:

$ cat /usr/local/cuda-9.2/version.txt                                                                                                                                                                        
CUDA Version 9.2.148

Cannot import name main

Problem

I got this error when I tried running pip:

    from pip import main
ImportError: cannot import name 'main'

Solution

I had installed pip from Ubuntu repositories using this command:

$ sudo apt install python-pip

However, I had previously used a pip from Anaconda on this computer. Though I had uninstalled it, it looked like it had left some files that were affecting how the Ubuntu pip worked.

I found the ~/.local/bin and ~/.local/lib directories that Anaconda pip had created and deleted those directories. Ubuntu pip worked fine after that.

Tried with: Ubuntu 16.04

Apt update stuck waiting for headers

Problem

I tried to update the apt cache on a machine that had not been updated in a long time:

$ sudo apt-get update

But that got stuck at one of the repositories Waiting for headers. No matter how many times I tried the command, it would get stuck at this.

Solution

The problem went away once I cleared the cache using these steps as explained here:

$ sudo apt-get clean
$ cd /var/lib/apt
$ sudo mv lists lists.old
$ sudo mkdir -p lists/partial
$ sudo apt-get clean
$ sudo apt-get update

Tried with: Ubuntu 16.04

How to exclude files from Explorer in VSCode

Visual Studio Code displays the files of the currently open workspace or folder in an Explorer on the left. Sometimes, you may want VSCode to exclude certain files from the Explorer.

To do that:

Go to File → Preferences → Settings.
If you want to exclude for all projects, open the User Settings. If you want to exclude only for the current project, open the Workspace Settings.
Add a files.exclude entry like this:

"files.exclude" : {
    "Makefile": true,
    "*.html": true,
    "build/*": true
}

As shown above, filenames and globbing are allowed.

Tried with: Visual Studio Code 1.25.1 and Windows 10

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