Having learned the basics of OpenGL in a 10 week university course that was primarily focused on modeling statistical data, I would definitely think OpenGL would be a reasonable option for an easy to learn graphics package for 2D real time modeling. Although there’s certainly complexity available to OpenGL you don’t need to wrap your … Read more
The error is actually “lvalue required as left operand of assignment”. It means that your a[i][j] is giving you a temporary object. This happens when you return from a function by value. A function call that returns by value is an rvalue expression, and you cannot use an rvalue expression as the left operand of an assignment. You need to … Read more
c_str returns a const char* that points to a null-terminated string (i.e. a C-style string). It is useful when you want to pass the “contents”¹ of an std::string to a function that expects to work with a C-style string. For example, consider this code: See it in action. Notes: ¹ This is not entirely true because an std::string (unlike a C string) … Read more
To quote the C++ standard, §3.9.1 ¶8: There are three floating point types: float, double, and long double. The type double provides at least as much precision as float, and the type long double provides at least as much precision as double. The set of values of the type float is a subset of the … Read more
Firstly you need to learn the differences between references and pointers and then the difference between pass-by-reference and pass-by-pointer. A function prototype of the form: expects a function call of the type: Whereas, a prototype of the form: expects a function call of the type: Using the same logic, if you wish to pass the vector by reference, … Read more
you should read about difference between pointers and reference that might help you understand your problem. In short, the difference is:when you declare myclass *p it’s a pointer and you can access it’s members with ->, because p points to memory location. But as soon as you call p=new myclass[10]; p starts to point to array and when you call p[n] you get a reference, which members … Read more
Well, data.str().c_str() yields a char const* but your function Printfunc() wants to have char*s. Based on the name, it doesn’t change the arguments but merely prints them and/or uses them to name a file, in which case you should probably fix your declaration to be The alternative might be to turn the char const* into a char* but fixing the declaration is preferable:
The address-operator & requires a variable to take the address from. The result of your cast (long)u32_Time is a temporary that does not necessarily reside in memory and therefore has no address that could be taken. So if that piece of code ever compiled somewhere it was a nonstandard compiler extension. The standard, §5.3.1,3 demands: The result of the … Read more
A functor is pretty much just a class which defines the operator(). That lets you create objects which “look like” a function: There are a couple of nice things about functors. One is that unlike regular functions, they can contain state. The above example creates a function which adds 42 to whatever you give it. … Read more
When the compiler compiles the class User and gets to the MyMessageBox line, MyMessageBox has not yet been defined. The compiler has no idea MyMessageBox exists, so cannot understand the meaning of your class member. You need to make sure MyMessageBox is defined before you use it as a member. This is solved by reversing the definition order. However, you have a cyclic dependency: if you move MyMessageBox above User, … Read more