{"id":360,"date":"2015-11-23T10:47:59","date_gmt":"2015-11-23T14:47:59","guid":{"rendered":"http:\/\/www.tayloraliss.com\/blog\/?p=360"},"modified":"2015-11-23T11:09:52","modified_gmt":"2015-11-23T15:09:52","slug":"pointers-round-2","status":"publish","type":"post","link":"https:\/\/www.tayloraliss.com\/blog\/?p=360","title":{"rendered":"Pointers: Round 2"},"content":{"rendered":"

Last Saturday I had my final exam for my CS161 course. I did\u00a0okay<\/em>, but I could have done better. I realize now that I really don’t have a handle on how pointers work still, so the goal of this post is to try and help myself understand them a little bit more.
\nI was watching some videos from The New Boston<\/a>\u00a0when I noticed that in the comments section\u00a0some people were saying that the video had mistakes. It’s a bit disheartening to hear that the people trying to teach you pointers can’t even get it right. I’m going to try and digest what was in the video and what the commentators said. Here’s my synopsis:<\/p>\n

Pass-by-reference uses references, not pointers. Pass-by-address<\/b> uses pointers. Pass-by-reference and pass-by-address are not the same thing. It’s an important distinction because pass-by-reference is handled differently when calling the function.<\/p>\n

A pass-by-reference function using references looks like this: passByReference(int &x);<\/code><\/p>\n

While a pass-by-address<\/b>\u00a0function using pointers\u00a0looks like this: passByAddress(int *x);<\/code><\/p>\n

The important difference here is that passByReference is used (called)\u00a0the same way as passByValue:<\/p>\n

passByReference(betty)<\/code><\/p>\n

passByValue(betty)<\/code><\/p>\n

A\u00a0passByAddress requires that you specify an address or a pointer as the argument. That is, you need to send a pointer\/address:<\/p>\n

int myVar = 5; \r\nint *myPointer = myVar; \/\/Pointer points to address of myVar\r\npassByPointer(myPointer)<\/pre>\n
or you need to put an ampersand (&) in front of your variable to denote it’s address rather than it’s value:<\/p>\n
passByAddress(&myVar)<\/code><\/p>\n
About the & operator<\/strong><\/h4>\n
“&” is for the\u00a0address of something. But<\/b> when used when declaring a new variable, it becomes a different thing.<\/p>\n
int a; <\/code><\/p>\n
&a;<\/code> \/\/ address of a<\/p>\n
int &a = b;<\/code> \/\/\u00a0the “&” now means you’re declaring a reference to “b”.<\/p>\n
Of course, when declaring a refence, you must immediately assign it to something. References must always refer to something, they can’t refer to nothing.<\/p>\n
So…<\/p>\n
int &a;<\/code> \/\/ not<\/b> valid<\/p>\n
int &a = b;<\/code> \/\/\u00a0valid<\/p>\n
To use it with function, you need to declare the function this way, to accept references:<\/p>\n
void function(int &a);<\/code> \/\/ takes a reference to an int<\/p>\n
And then you just send any “int” to it:<\/p>\n
int a;\r\nfunction(a);<\/pre>\n
It looks<\/b> like<\/b> we’re sending the value of “a”, but because the function was declared to accept references, not values,\u00a0you’re actually sending a reference to it.<\/p>\n
——<\/p>\n
I also found some help from this StackOverflow<\/a> thread:<\/p>\n
void makePointerEqualSomething(int *pInteger)\r\n{\r\n *pInteger = 7;\r\n}<\/pre>\n
In the function declaration<\/strong>, * means you are passing a pointer, but in its actual code body<\/strong>\u00a0* means you are accessing what the pointer is pointing at.<\/p>\n
In the function declaration, * means you are passing a pointer, but in its actual code body * means you are accessing what the pointer is pointing at.<\/p>\n
& means get the address of something, its exact location in the computers memory, so int &myVariable;<\/code>\u00a0<\/span><\/span>i<\/span>n a <\/span>declaration<\/strong> means the address<\/strong> of an integer or a pointer, while<\/span><\/p>\n
int *pInteger;\r\nint someData;\r\npInteger = &someData;<\/pre>\n
means make the pInteger<\/code>\u00a0pointer equal to the address<\/strong> of ‘someData’ – so now pInteger<\/code>\u00a0points at someData<\/code> and can be used to access it when you deference it:<\/p>\n
*pInteger = 9000;<\/code><\/p>\n
You can read that last line as “what is at the memory address pInteger\u00a0points to is equal to 9000.”<\/p>\n","protected":false},"excerpt":{"rendered":"
Last Saturday I had my final exam for my CS161 course. I did\u00a0okay, but I could have done better. I realize now that I really don’t have a handle on how pointers work still, so the goal of this post is to try and help myself understand them a little bit more. I was watching […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-360","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/www.tayloraliss.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/360","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.tayloraliss.com\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.tayloraliss.com\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.tayloraliss.com\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.tayloraliss.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=360"}],"version-history":[{"count":10,"href":"https:\/\/www.tayloraliss.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/360\/revisions"}],"predecessor-version":[{"id":377,"href":"https:\/\/www.tayloraliss.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/360\/revisions\/377"}],"wp:attachment":[{"href":"https:\/\/www.tayloraliss.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=360"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.tayloraliss.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=360"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.tayloraliss.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=360"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}