What does the * mean when in a C++ method signature?

Question

I know enough that a * relates to a pointer. I'm still trying to sort that out in my head (pointers versus references.)

I'm working through a C++ book and there is a method signature in it like this:

void DrawBitmap(char *filename, int x, int y)

What does the * mean in this situation? is it accepting a pointer, or a reference to a variable?

Thanks for any help... and for putting up with an admittedly noob question.

It expects an _array_ of `char`-s (the C way of representing a string). The array is passed as a pointer to the first element. — James M, Apr 14 '12 at 20:10
@JamesMcLaughlin In fact it is a pointer rather than an array — David Heffernan, Apr 14 '12 at 20:11
If you have a **C++** book teaching you to do things like that, then you might be learning from a very outdated book. It looks as if it's trying to teach you the C language first (That used to be the done thing back in the 1990s, but not in 2012). C++ includes a `string` type for handling strings - passing _char*_ to a function is a very outdated way of doing things. — Ben Cottrell, Apr 14 '12 at 20:14
the book is Beginner Game Programming with C++. I'm actually a bit disappointed with it because it doesn't really explain C++ that much. At one point, the author even says that instead of explaing pointers he rather that readers of his book just use them and we'll get it eventually. — quakkels, Apr 14 '12 at 20:15
Time to get a better book. Don't worry about game programming. Learn to program, and then think about game specific techniques. For books, refer to this excellent Q: http://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list — David Heffernan, Apr 14 '12 at 20:16
I've been professionally programming C# for a couple years now. My programming knowledge so far has been higher level to this point. I want to get in games programming as a hobby and I would LOVE to learn a foundational language like C++. Thanks for the link too. — quakkels, Apr 14 '12 at 20:20

score 5 · Accepted Answer · answered Apr 14 '12 at 20:11

5

It means that you're passing it a pointer to a character, which usually means that pointer points to the first character in an array of characters. With a pointer (*), you can do arithmetic, e.g. (fileName + 1) to get the second character. When you use a reference (&), you are implying that the receiving function should operate on the original data. Without the reference, the function is passed a copy, rather than the original.

answered Apr 14 '12 at 20:11

Gordon

1,844
4
17
32

Very succinct. Thanks for your answer. – quakkels Apr 14 '12 at 20:16
"When you use a reference (&), you are implying" -- very poor choice of words. You're not 'implying' anything. – George Skoptsov Apr 14 '12 at 21:33
Please provide a better choice of words, then, and tell me how it offers no implication. – Gordon Apr 20 '12 at 05:46

score 1 · Answer 2 · answered Apr 14 '12 at 20:19

Others have directly answered your question already; some of the following links are well worth a read for information about pointers (and their syntactical relationship to arrays in C++), they're well worth studying and I would recommend taking a little time reading through them to get your head around the ideas:

http://www.c-faq.com/aryptr/

http://www.augustcouncil.com/~tgibson/tutorial/ptr.html

http://www.augustcouncil.com/~tgibson/tutorial/arr.html

http://www.eternallyconfuzzled.com/tuts/languages/jsw_tut_pointers.aspx

http://www.daweidesigns.com/cgi-bin/pointers.php