Tutorial by Examples: am

My C++ program ends with segfault - valgrind

Let's have a basic failing program: #include <iostream> void fail() { int *p1; int *p2(NULL); int *p3 = p1; if (p3) { std::cout << *p3 << std::endl; } } int main() { fail(); } Build it (add -g to include debug info): g++ -g -o m...

C++ • C++ Debugging and Debug-prevention Tools & Techniques

Using let in loops instead of var (click handlers example)

Let's say we need to add a button for each piece of loadedData array (for instance, each button should be a slider showing the data; for the sake of simplicity, we'll just alert a message). One may try something like this: for(var i = 0; i < loadedData.length; i++) jQuery("#container&q...

JavaScript • Scope

List a module's functions or macros

The __info__/1 function takes one of the following atoms: :functions - Returns a keyword list of public functions along with their arities :macros - Returns a keyword list of public macros along with their arities To list the Kernel module’s functions: iex> Kernel.__info__ :functions [...

Elixir Language • Modules

Keyword lists as function parameters

Use keyword lists for 'options'-style parameters that contains multiple key-value pairs: def myfunc(arg1, opts \\ []) do # Function body end We can call the function above like so: iex> myfunc "hello", pizza: true, soda: false which is equivalent to: iex> myfunc("he...

Elixir Language • Functions

Calling a method

assert ['cat', 'dog', 'fish']*.length() == [3, 3, 4] Note that when mixing types in the collection if the method not exists on some of the elements, a groovy.lang.MissingMethodException could be thrown: ['cat', 'dog', 'fish',3]*.length() // it throws groovy.lang.MissingMethodException: No sign...

groovy • Spread Operator

Example showcasing the basic concepts

The following example is an introduction to: Template compilation using underscore Accessing variables in a template Creating a view Rendering a view Showing a view <html> <head> <script src="https://code.jquery.com/jquery-3.1.0.min.js"></script> ...

backbone.js • Getting started with backbone.js

Joining Examples

Query to create table on db CREATE TABLE `user` ( `id` smallint(5) unsigned NOT NULL AUTO_INCREMENT, `name` varchar(30) NOT NULL, `course` smallint(5) unsigned DEFAULT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB; CREATE TABLE `course` ( `id` smallint(5) unsigned NOT NULL AUTO_INCREMENT, `nam...

MySQL • Joins

Basic sample

Unlike other middleware functions error-handling middleware functions have four arguments instead of three: (err, req, res, next). Sample: app.use(function(err, req, res, next) { console.error(err.stack); res.status(500).send('Error found!'); });

express • Error handling

Creating a module

A module is an importable file containing definitions and statements. A module can be created by creating a .py file. # hello.py def say_hello(): print("Hello!") Functions in a module can be used by importing the module. For modules that you have made, they will need to be in t...

Python Language • Getting started with Python Language

Simple example

Directives, as the name suggests, are direction or instructions for the container to follow when translating a JSP to a servlet. There are 3 directives namely page, include and taglib which you can use in your JSP. Below is a simple example of using page directive: <%@ page isErrorPage="tr...

jsp • Directives

Making Dynamic HTML Maps with Leaflet

Leaflet is an open-source JavaScript library for making dynamic maps for the web. RStudio wrote R bindings for Leaflet, available through its leaflet package, built with htmlwidgets. Leaflet maps integrate well with the RMarkdown and Shiny ecosystems. The interface is piped, using a leaflet() funct...

R Language • Introduction to Geographical Maps

Without parameters

This example shows how to create a delegate that encapsulates the method that returns the current time static DateTime UTCNow() { return DateTime.UtcNow; } static DateTime LocalNow() { return DateTime.Now; } static void Main(string[] args) { Func<DateTime> method = U...

C# Language • Func delegates

Lambda & anonymous methods

An anonymous method can be assigned wherever a delegate is expected: Func<int, int> square = delegate (int x) { return x * x; } Lambda expressions can be used to express the same thing: Func<int, int> square = x => x * x; In either case, we can now invoke the method stored ins...

C# Language • Func delegates

Covariant & Contravariant Type Parameters

Func also supports Covariant & Contravariant // Simple hierarchy of classes. public class Person { } public class Employee : Person { } class Program { static Employee FindByTitle(String title) { // This is a stub for a method that returns // an employee that h...

C# Language • Func delegates

Names in code vs names in `use`

The double-colon syntax of names in the use statement looks similar to names used elsewhere in the code, but meaning of these paths is different. Names in the use statement by default are interpreted as absolute, starting at the crate root. Names elsewhere in the code are relative to the current mo...

Rust • Modules

Converting an error code into a message string

GetLastError returns a numerical error code. To obtain a descriptive error message (e.g., to display to a user), you can call FormatMessage: // This functions fills a caller-defined character buffer (pBuffer) // of max length (cchBufferLength) with the human-readable error message // for a Win32 ...

Win32 API • Error reporting and handling

Using a typealias to name your tuple type

Occasionally you may want to use the same tuple type in multiple places throughout your code. This can quickly get messy, especially if your tuple is complex: // Define a circle tuple by its center point and radius let unitCircle: (center: (x: CGFloat, y: CGFloat), radius: CGFloat) = ((0.0, 0.0), ...

Swift Language • Tuples

Countdown timer example

package { import flash.events.TimerEvent; import flash.utils.Timer; public class CountdownTimer extends Timer { public var time:Number = 0; public function CountdownTimer(time:Number = Number.NEGATIVE_INFINITY, delay:Number = 1000) { super(delay, repeatCount); ...

ActionScript 3 • Working with Timers

Sample Rate

ga('create', 'UA-XXXX-Y', {'sampleRate': 5}); Optional. This may only be set in the create method. Specifies what percentage of users should be tracked. This defaults to 100 (no users are sampled out) but large sites may need to use a lower sample rate to stay within Google Analytics processing ...

google-analytics • Sampling

Default parameters

Before ECMAScript 2015 (ES6), a parameter's default value could be assigned in the following way: function printMsg(msg) { msg = typeof msg !== 'undefined' ? // if a value was provided msg : // then, use that value in the reassignemnt 'Default value for ...

JavaScript • Functions