Problem:
You have a filename in the Linux shell and want to strip/remove the filename extension from it – e.g. if you have myarchive.zip
, you want to get only myarchive
as output.
You have a filename in the Linux shell and want to strip/remove the filename extension from it – e.g. if you have myarchive.zip
, you want to get only myarchive
as output.
In C/C++ you want to encode/decode something from/to Base64. libtomcrypt is WTFPL-licensed and therefore provides a good choice for both commercial and non-commercial projects.
You want to calculate a hash of any string in C/C++. LibTomCrypt is WTFPL licensed, so it’s a good choice for commercial and non-commercial projects.
Recently hackthissite.org was recommended to me — it’s really fun to play around with, even if I think some of the challenges are not that realistic any more.
I thought it would be just as much fun to post some of my solutions to the programming challenges here. If not absolutely neccessary for understanding the underlying algorithm, I won’t post any information about how to use the programs, because the purpose of these posts shall be to understand it, not to use it in order to solve the HTS challenges.
You want to view a VNC on a screen with a different resolution than the screen you’re viewing (e.g. you want to view your Full HD desktop display on your Notebook).
Usually VNC viewers show scroll bars, but in some cases you need to view the entire screen at once.
In GNU R, you have an arbitrary string s and want to count how often a given character occurs in s.
You want to use a custom column type for your LaTeX tabular that has a specific font attribute (we’ll use the font family for this example).
You’re using Maven as build system but you need to include your Java sources into your JAR file generated by mvn package
.
In many cases if you want to create an interactive command line interface, you need to check if a number entered by the user is valid and – if it isn’t – you want the user to re-input it.
Here’s a simple static method to check if a number typed by a user is within a given boundary:
/**
* Lets the user input an integer value until it satisfies the given
* conditions
*
* @param msg The prompt to ask the user for the value.
* @param lower The lower boundary, inclusive
* @param upper The upper boundary, inclusive
*/
private static int guardedInput(String msg, int lower, int upper) {
Scanner scanner = new Scanner(System.in);
while (true) {
System.out.print(msg);
int val = -1;
try {
val = scanner.nextInt();
} catch (InputMismatchException ex) {
System.out.println("Illegal value: Please type a number!");
}
if (val < lower) {
System.out.println("Illegal value: Must be greater than " + (lower - 1));
} else if (val > upper) {
System.out.println("Illegal value: Must be smaller than " + (upper + 1));
} else {
return val;
}
}
}
When running any npm
command, you get a stacktrace similar to the following:
Error: Cannot find module 'graceful-fs' at Function.Module._resolveFilename (module.js:338:15) at Function.Module._load (module.js:280:25) at Module.require (module.js:362:17) at require (module.js:378:17) at Object.<anonymous> (/usr/share/npm/lib/utils/ini.js:32:10) at Module._compile (module.js:449:26) at Object.Module._extensions..js (module.js:467:10) at Module.load (module.js:356:32) at Function.Module._load (module.js:312:12) at Module.require (module.js:362:17)
When executing node-waf
, you get the following error message:
Traceback (most recent call last): File "/usr/local/bin/node-waf", line 14, in <module> import Scripting ImportError: No module named Scripting
This also prevents node modules with native components to be built.
Instead of having to buy expensive JTAG adapters like the Xilinx Platform Cable USB, Digilent FPGA boards like the Nexys3 support programming by using the Adept protocol being translation into JTAG internally. The Adept software is pretty easy to use if you know the basics of how to use the executables.
This is a beginner’s tutorial, so if you already have some experience with FPGAs, you might want to skip some parts. Still you need to have some knowledge about how to use the shell.
In C++11 you want to iterate over a smart pointer (auto_ptr
, shared_ptr
, …). collection, say a std::vector
, using the new for
loop syntax.
Let’s try it out:
using namespace std; shared_ptr<vector<int> > smartptr(/* A ptr to your vector */); for(int s : smartptr) { /* do something useful */ }
When trying to compile this code, GCC emits the following error message (other lines are omitted for the sake of simplicity)
error: no matching function for call to 'begin(std::shared_ptr<std::vector<int> >&)' error: no matching function for call to 'end(std::shared_ptr<std::vector<int> >&)'
or, when LANG=de
is set:
Fehler: keine passende Funktion für Aufruf von »begin(std::shared_ptr<std::vector<int> >&)« Fehler: keine passende Funktion für Aufruf von »end(std::shared_ptr<std::vector<int> >&)«
In NodeJS, you got a size of a file in bytes, but you want to format it for better readability.
For example, if your size is 10000
bytes, you want to print 10 kilobytes
, but if it is 1200000
, you want to print 1.20 Megabytes
.
To determine the size of a file in NodeJS (e.g. to get the size of myfile.txt
) use fs.stat()
or fs.statSync()
like this:
const fs = require("fs"); //Load the filesystem module const stats = fs.statSync("myfile.txt"); const fileSizeInBytes = stats.size; //Convert the file size to megabytes (optional) const fileSizeInMegabytes = fileSizeInBytes / 1000000.0;
Another option is to use the following function:
function getFilesizeInBytes(filename) { const stats = fs.statSync(filename); const fileSizeInBytes = stats.size; return fileSizeInBytes; }