"const" means that the parameter is constant and the compiler will not allow changing its value.
"&" is a reference to a particular parameter. If you call a function with a parameter that is not a reference then a copy is made of what you passed in. If it is a reference then basically the caller and the function are both pointing to the same place in memory and any edits the function makes to it will be seen by the caller. For objects that are non-trivial it can be quite time consuming to make copies to be passed to functions so it is common to pass these objects around "by reference". If you don't want the function changing anything in your object, but you also don't want to be spending the time copying it then you can combine a reference with const and have a "const reference". eg. one of the constructors for MAngle takes in a const reference to another MAngle. In this example there isn't a copy made of "MAngle src" but if the constructor tried to change something in src then there would be a compiler error spit out. * is a pointer to a location in memory. When you say something like "SomeObject * var;" this means that var is a variable which stores a memory address and that the object at that location in memory is of type "SomeObject". Passing pointers to objects, instead of the objects themselves, is like passing the object by reference in that just a copy of the pointer is made instead of copying the actual object. When you declare a function parameter like this: "bool calculateExactHit = false" this means that that paramater is optional and if the caller doesn't specify a value for it then what you have provided there will be used. You can have a mixture of non-optional and optional paramaters in a function. eg. void someFunction(int a, int b, int c = 5, int d = 5); could be called like: someFunction(1, 2) <- c and d will both be 5 here someFunction(1, 2, 3) <- c will be 3 and d will be 5 someFunction(1, 2, 3, 4) <- c will be 3 and d will be 4 In this example of yours: bool calculateExactHit = false, bool * wasExactHit = NULL, calculateExactHit is a boolean and if you don't specify a value for it then the function will use false. wasExactHit is a pointer to a memory location, and the value at that location in memory should be interpreted as a boolean. NULL is a special value for pointers that basically says that it's not really a memory location, or it's not initialized to something yet. So if you don't specify something for "wasExactHit" then the pointer will be set to NULL. Then in the implementation, the function can compare the value to NULL to determine if it's valid or not. That probably doesn't answer everything you've asked...but might get you a little farther along :-) On Sun, Feb 15, 2009 at 5:16 PM, jasonosipa <[email protected]> wrote: > > What do const, &, and * each mean? > > When you look at documentation for an object, each argument can have a > lot of different markup, and I'm not confident with guesses at what > those mean, so I'll just ask: > > What do const, &, and * each mean? What does "blank" mean, where > there is no const at the head of the line, and no * or & ? How about > the stuff after the = in the argument? Is that just a "recommended > default"? Does const only show up for things that are MObjects? > > Why is it that something like these two argument lines: > > bool calculateExactHit = false, > bool * wasExactHit = NULL, > > Both seem to be booleans, but one has no markup, and what looks like a > "default suggestion" of false, which fits into the idea of a boolean, > whereas the second has a star between, and then has a "default > suggestion" of NULL. Are those not default suggestions? If they are > - I'd have to use None not NULL in python, right? Knowing what > const, & and * each means is the answer to all of these questions, > isn't it... > > > --~--~---------~--~----~------------~-------~--~----~ Yours, Maya-Python Club Team. -~----------~----~----~----~------~----~------~--~---
