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• Linear complexity and quadratic complexity

  - by jasonline

  I'm just not sure... If you have a code that can be executed in either of the following complexities: A sequence of O(n), like for example: two O(n) in sequence O(n²) The preferred version would be the one that can be executed in linear time. Would there be a time such that the sequence of O(n) would be too much and that O(n²) would be preferred? In other words, is the statement C x O(n) < O(n²) always true for any constant C? Why or why not? What are the factors that would affect the condition such that it would be better to choose the O(n²) complexity?

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• Modifying a const through a non-const pointer

  - by jasonline

  I'm a bit confused what happened in the following code: const int e = 2; int* w = ( int* ) &e; // (1) cast to remove const-ness *w = 5; // (2) cout << *w << endl; // (3) outputs 5 cout << e << endl; // (4) outputs 2 cout << "w = " << w << endl; // (5) w points to the address of e cout << "&e = " << &e << endl; In (1), w points to the address of e. In (2), that value was changed to 5. However, when the values of *w and e were displayed, their values are different. But if you print value of w pointer and &e, they have the same value/address. How come e still contained 2, even if it was changed to 5? Were they stored in a separate location? Or a temporary? But how come the value pointed by w is still the address of e?

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• Revision histories and documenting changes

  - by jasonline

  I work on legacy systems and I used to see revision history of files or functions being modified every release in the source code, for example: // // Rev. No Date Author Description // ------------------------------------------------------- // 1.0 2009/12/01 johnc <Some description> // 1.1 2009/12/24 daveb <Some description> // ------------------------------------------------------- void Logger::initialize() { // a = b; // Old code, just commented and not deleted a = b + c; // New code } I'm just wondering if this way of documenting history is still being practiced by many today? If yes, how do you apply modifications on the source code - do you comment it or delete it completely? If not, what's the best way to document these revisions? If you use version control systems, does it follow that your source files contain pure source codes, except for comments when necessary (no revision history for each function, etc.)?

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• Protocol error in TDS stream

  - by jasonline

  What are the possible causes of this type of error - "[Microsoft][ODBC SQL Server Driver]Protocol error in TDS stream"? And how can this be fixed? My application runs in C++ calling stored procedures implemented in SQL Server. There's this one SP (containing select and update statements) that causes this problem, after which all succeeding queries will return that the cursor is in an invalid state. I've checked the SP but I don't see any possible problem.

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• Overloading assignment operator in C++

  - by jasonline

  As I've understand, when overloading operator=, the return value should should be a non-const reference. A& A::operator=( const A& ) { // check for self-assignment, do assignment return *this; } It is non-const to allow non-const member functions to be called in cases like: ( a = b ).f(); But why should it return a reference? In what instance will it give a problem if the return value is not declared a reference, let's say return by value?

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• How do you make a private member in the base class become a public member in the base class?

  - by jasonline

  Consider the following code: class Base { void f() { } }; class Derived: public Base { public: }; What can you change in the derived class, such that you can perform the following: Derived d; d.f(); If the member is declared as public in the base class, adding a using declaration for Base::f in the derived class public section would've fix the problem. But if it is declared as private in the base class, this doesn't seem to work.

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• Linear time and quadratic time

  - by jasonline

  I'm just not sure... If you have a code that can be executed in either of the following complexities: (1) A sequence of O(n), like for example: two O(n) in sequence (2) O(n²) The preferred version would be the one that can be executed in linear time. Would there be a time such that the sequence of O(n) would be too much and that O(n²) would be preferred? In other words, is the statement C x O(n) < O(n²) always true for any constant C? If no, what are the factors that would affect the condition such that it would be better to choose the O(n²) complexity?

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• STL deque accessing by index is O(1)?

  - by jasonline

  I've read that accessing elements by position index can be done in constant time in a STL deque. As far as I know, elements in a deque may be stored in several non-contiguous locations, eliminating safe access through pointer arithmetic. For example: abc-defghi-jkl-mnop The elements of the deque above consists of a single character. The set of characters in one group indicate it is allocated in contiguous memory (e.g. abc is in a single block of memory, defhi is located in another block of memory, etc.). Can anyone explain how accessing by position index can be done in constant time, especially if the element to be accessed is in the second block? Or does a deque have a pointer to the group of blocks? Update: Or is there any other common implementation for a deque?

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• What are common uses of condition variables in C++?

  - by jasonline

  I'm trying to learn about condition variables. I would like to know what are the common situations where condition variables are used. One example is in a blocking queue, where two threads access the queue - the producer thread pushes an item into the queue, while the consumer thread pops an item from the queue. If the queue is empty, the consumer thread is waiting until a signal is sent by the producer thread. What are other design situations where you need a condition variable to be used?

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