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What is the purpose of XORing a register with itself? [duplicate]
...t is more efficient.
The opcode is shorter than mov eax, 0, only 2 bytes, and the processor recognizes the special case and treats it as a mov eax, 0 without a false read dependency on eax, so the execution time is the same.
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Why doesn't delete set the pointer to NULL?
...tomatic setting of the pointer to NULL after delete is not part of the standard. If this gets taken care of then many of the crashes due to an invalid pointer would not occur. But having said that I can think of couple of reasons why the standard would have restricted this:
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How to create war files
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You can use Ant to set up, compile, WAR, and deploy your solution.
<target name="default" depends="setup,compile,buildwar,deploy"></target>
You can then execute one click in Eclipse to run that Ant target. Here are examples of each of the steps:
Prec...
How to create custom exceptions in Java? [closed]
... it:
public void calculate(int i) throws FooException, IOException;
... and code calling this method must either handle or propagate this exception (or both):
try {
int i = 5;
myObject.calculate(5);
} catch(FooException ex) {
// Print error and terminate application.
ex.printStackTrace()...
Handling optional parameters in javascript
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You can know how many arguments were passed to your function and you can check if your second argument is a function or not:
function getData (id, parameters, callback) {
if (arguments.length == 2) { // if only two arguments were supplied
if (Object.prototype.toString.call(param...
How to enumerate an object's properties in Python?
...). Setting values directly on the dictionary bypasses the object's setter (and/or its parents'). It's quite common in python that more things than meet the eye are happening in the background during attribute setting (e.g. sanitation), using setattr() ensures that you don't miss out, or are forced t...
Creating an empty file in C#
...a difference is if the thread were aborted between the call to File.Create and the call to Dispose. If that race condition exists, I suspect it would also exist in the using version, if the thread were aborted at the very end of the File.Create method, just before the value was returned...
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Uses for the Java Void Reference Type?
...tions.newSetFromMap uses Boolean as maps don't have to accept null values) and java.security.PrivilegedAction.
I wrote a weblog entry on Void a few years back.
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Is there a difference between x++ and ++x in java?
Is there a difference between ++x and x++ in java?
16 Answers
16
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Is there a way to access the “previous row” value in a SELECT statement?
...u want to order alphabetically) then I don't know of a way to do that in standard SQL, but most SQL implementations will have extensions to do it.
Here is a way for SQL server that works if you can order rows such that each one is distinct:
select rank() OVER (ORDER BY id) as 'Rank', value into...