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Is it legal and moral for a member function to say delete this? This includes code that will run in destructors for any objects allocated on the stack that are still alive.
In other words, you must not examine it, compare it with another pointer, compare it with nullptr, print it, cast it, do anything with it. How do I allocate multidimensional arrays using new?
There are many ways to do this, depending on how flexible you want the array sizing to be. On std map copy-on-write array extreme, if you know all the dimensions at compile-time, you can allocate multidimensional arrays statically as in C: In the following function, ncols[i] is the number of columns in row number i, where i varies between 0 and nrows-1 inclusive.
This prevents wrap-around of the unsigned value when i goes one step below zero. Finally, note that pointers and arrays are evil. It is normally much better to encapsulate your pointers in a class that has a safe and simple interface.
The following FAQ shows how to do this. The reason the code in the previous FAQ was so tricky and error prone was that it used pointers, and we know that pointers and arrays are evil.
The solution is to encapsulate your pointers in a class that has a safe and simple interface. For example, we can define a Matrix class that handles a rectangular matrix so our user code will be vastly simplified when compared to the the rectangular matrix code from the previous FAQ: Matrix unsigned nrows, unsigned ncols: The latter point is important.
For example, assuming Matrix is even mildly reusable, moving complexity from the users [plural] of Matrix into Matrix itself [singular] is equivalent to moving complexity from the many to the few.
Anyone who has seen Star Trek 2 knows that the good of the many outweighs the good of the few… or the one. But the above Matrix class is specific to Fred! Yep; just use templates: For example, the following uses a Matrix of std:: Use the standard vector template, and make a vector of vector.
The following uses a std:: Simply put, your code is a lot less likely to have memory leaks if you use std:: Note also that std:: Yes, in the sense that the standard library has a std:: No, in the sense that built-in array types need to have their length specified at compile time.
Yes, in the sense that even built-in array types can specify the first index bounds at run-time. Use some object of some class if you can. Use arrays only when you have to.
How can I force objects of my class to always be created via new rather than as local, namespace-scope, global, or static?
Use the Named Constructor Idiom. In this case the create methods allocate the objects via new. Since the constructors themselves are not public, there is no other way to create objects of the class.
Note also that you can make another class Wilma a friend of Fred if you want to allow a Wilma to have a member object of class Fred, but of course this is a softening of the original goal, namely to force Fred objects to be allocated via new.
How do I do simple reference counting? One of the implicit constraints on FredPtr is that it must only point to Fred objects which have been allocated via new. Thus no one could accidentally subvert the reference counting mechanism. For example, if Fred had a Fred:: Fred and a Fred:: Fred int i, int jthe changes to class Fred would be: How do I provide reference counting with copy-on-write semantics?
Reference counting can be done with either pointer semantics or reference semantics.Yes, in the sense that even built-in array types can specify the first index bounds at run-time.
E.g., comparing with the previous FAQ, if you only need the first array dimension to vary then you can just ask new for an array of arrays, rather than an array of pointers to arrays.
Memory Mapped Files And Shared Memory For C++ Contents. Introduction; Memory Mapped Files; //Map the whole file std::mapped_region region(*attheheels.com(), std::mapped_region::copy_on_write); Shared memory stream classes.
If basic_filebuf is defined as a mappable object, we could create the shared memory equivalent of this class. This would. Code performance always matters, and copying data is a common operation.
Simple array copy code uses a loop to copy one value at a time. ISO C provides the memcpy() and memmove() functions to do this efficiently, but are they faster, by how much, and under what conditions?This article benchmarks five common methods and four common compilers to find the fastest method to copy an array quickly.
Historically, the string data has not been const because it would prevent several common optimizations, like copy-on-write (COW). This is now, IIANM, far less common, because it behaves badly with multithreaded programs.
I would like to make an std::list of arrays. specifically, I want a list of arrays of Borland Code Builders AnsiStrings. the real kicker being .
If you simply want to check whether a QByteArray contains a particular character or substring, use contains(). If you want to find out how many times a particular character or substring occurs in the byte array, use count(). If you want to replace all occurrences of a particular value with another, use one of the two-parameter replace() overloads.