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Safely override C++ virtual functions
I have a base class with a virtual function and I want to override that function in a derived class. Is there some way to make the compiler check if the function I declared in the derived class actually overrides a function in the base class? I would like to add some macro or something that ensures ...
Get top n records for each group of grouped results
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Here is one way to do this, using UNION ALL (See SQL Fiddle with Demo). This works with two groups, if you have more than two groups, then you would need to specify the group number and add queries for each group:
(
select *
from mytable
where `group` = 1
order by age desc
...
HTML encoding issues - “” character showing up instead of “ ”
... legacy app just starting to misbehave, for whatever reason I'm not sure. It generates a bunch of HTML that gets turned into PDF reports by ActivePDF.
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What's the point of malloc(0)?
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According to the specifications, malloc(0) will return either "a null pointer or a unique pointer that can be successfully passed to free()".
This basically lets you allocate nothing, but still pass the "artist" variable to a call to free() without worry. For practical purposes,...
Polymorphism in C++
...m
To understand polymorphism - as the term is used in Computing Science - it helps to start from a simple test for and definition of it. Consider:
Type1 x;
Type2 y;
f(x);
f(y);
Here, f() is to perform some operation and is being given values x and y as inputs.
To exhibit po...
Wait until all jQuery Ajax requests are done?
How do I make a function wait until all jQuery Ajax requests are done inside another function?
20 Answers
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Java Class.cast() vs. cast operator
...lt;T> T doSomething() {
Object o;
// snip
return (T) o;
}
It's often best to replace it by:
<T> T doSomething(Class<T> cls) {
Object o;
// snip
return cls.cast(o);
}
That's the only use case for Class.cast(Object) I've ever come across.
Regarding compiler...
std::string to char*
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It won't automatically convert (thank god). You'll have to use the method c_str() to get the C string version.
std::string str = "string";
const char *cstr = str.c_str();
Note that it returns a const char *; you aren't all...
How do I pass a string into subprocess.Popen (using the stdin argument)?
...nd data to
the process’s stdin, you need to
create the Popen object with
stdin=PIPE. Similarly, to get anything
other than None in the result tuple,
you need to give stdout=PIPE and/or
stderr=PIPE too.
Replacing os.popen*
pipe = os.popen(cmd, 'w', bufsize)
# ==>
p...
Set size on background image with CSS?
Is it possible to set the size of the background image with CSS?
18 Answers
18
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