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What uses are there for “placement new”?
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Placement new allows you to construct an object in memory that's already allocated.
You may want to do this for optimization when you need to construct multiple instances of an object, and it is faster not to re-allocate memory each time you need a new instance. Instead, it might be more efficien...
What are Runtime.getRuntime().totalMemory() and freeMemory()?
...hy there is a totalMemory() AND a maxMemory(). The answer is that the JVM allocates memory lazily. Lets say you start your Java process as such:
java -Xms64m -Xmx1024m Foo
Your process starts with 64mb of memory, and if and when it needs more (up to 1024m), it will allocate memory. totalMemory...
STL中map容器使用自定义key类型报错详解 - C/C++ - 清泛网 - 专注C/C++及内核技术
...对正在编译的类 模板 实例化“std::_Tmap_traits<_Kty,_Ty,_Pr,_Alloc,_Mfl>”的引用
1> with
1> [
1> _Kty=a,
1> _Ty=int,
1> _Pr=std::less<a>,
1> _Alloc=std::allocator<std::pair<const a,int>>,
1> _Mf...
C++ new int[0] — will it allocate memory?
... When the value of the expression in a direct-new-declarator is zero, the allocation function is called to allocate an array with no elements.
From 3.7.3.1/2
The effect of dereferencing a pointer returned as a request for zero size is undefined.
Also
Even if the size of the space reques...
Which is a better way to check if an array has more than one element?
...languages. Many programmers expect sizeof() to return the amount of memory allocated.
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What's the Hi/Lo algorithm?
...erability with other 3rd-party clients that are not aware of this sequence allocation strategy.
Being both efficient and interoperable with other systems, the pooled-lo optimizer is a much better candidate than the legacy hi/lo identifier strategy.
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When vectors are allocated, do they use memory on the heap or the stack?
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vector<Type> vect;
will allocate the vector, i.e. the header info, on the stack, but the elements on the free store ("heap").
vector<Type> *vect = new vector<Type>;
allocates everything on the free store.
vector<Type*> vect;
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How does delete[] “know” the size of the operand array?
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When you allocate memory on the heap, your allocator will keep track of how much memory you have allocated. This is usually stored in a "head" segment just before the memory that you get allocated. That way when it's time to free the ...
How to add 2 buttons into the UINavigationbar on the right side without IB?
...ith iOS 5+ it's as easy as:
UIBarButtonItem *btnShare = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAction target:self action:@selector(share)];
UIBarButtonItem *btnRefresh = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemRefresh target:self ...
Why malloc+memset is slower than calloc?
It's known that calloc is different than malloc in that it initializes the memory allocated. With calloc , the memory is set to zero. With malloc , the memory is not cleared.
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