{"id":24621,"date":"2022-12-04T11:51:16","date_gmt":"2022-12-04T06:21:16","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-dereferencing-a-double-level-pointer-results-in-different-behaviour-from-dereferencing-a-single-level-pointer\/"},"modified":"2022-12-04T11:51:16","modified_gmt":"2022-12-04T06:21:16","slug":"solved-dereferencing-a-double-level-pointer-results-in-different-behaviour-from-dereferencing-a-single-level-pointer","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-dereferencing-a-double-level-pointer-results-in-different-behaviour-from-dereferencing-a-single-level-pointer\/","title":{"rendered":"[Solved] Dereferencing a double-level pointer results in different behaviour from dereferencing a single-level pointer"},"content":{"rendered":"

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They are very different things. An int**<\/code> is a pointer to a pointer to an int<\/code>. If you dereference it, you get an int*<\/code>. An int*<\/code> is a pointer to an int<\/code>. If you dereference it, you get an int<\/code>.<\/p>\n

In the first example, you pass an int**<\/code> with value 0x4df73c<\/code> as the first argument to work<\/code>. You then dereference this, which should give you an int*<\/code>. That is, 0x4df73c<\/code> is the address of an address and doing *pointer<\/code> has gotten you the second addess. You then do pointer arithmetic with this int*<\/code> by adding (offset\/sizeof(int))<\/code>, which works out how many int<\/code>s there are with offset<\/code> bytes. So when you add this value, your int*<\/code> will move along to point at the int<\/code> at that offset. You then return this int*<\/code> and all is well.<\/p>\n

In the second example, you pass 0x4df73c<\/code> as an int*<\/code>. You then dereference it, which gives you an int<\/code>. Now the +<\/code> doesn’t do pointer arithmetic – it does integer arithmetic. (offset\/sizeof(int))<\/code> will still give you the number of int<\/code>s in offset<\/code> bytes, but the arithmetic won’t do what you want. It won’t increase the value of the int<\/code> by the appropriate amount.<\/p>\n

Let’s say an int<\/code> is 4 bytes on your machine. When you have an int*<\/code> called p<\/code> and you do p + 5<\/code>, this doesn’t just add 5<\/code> to the address in p<\/code>. It adds 5<\/code> times the size of an int<\/code> (20 bytes), so that it’s now pointing at the 5th int<\/code>. However, if you have an int<\/code> called i<\/code> and you do i + 5<\/code>, this really does just add 5<\/code>.<\/p>\n

So that’s your problem. When you add to the int<\/code>, you’re not doing the appropriate arithmetic<\/strong>. I imagine it would<\/em> work if you change it to, assuming an int*<\/code> and an int<\/code> are the same size on your system (as you say they are):<\/p>\n

return (int*) (*pointer + offset);\n<\/code><\/pre>\n
but I do not recommend this<\/em>. Don’t use an int<\/code> as though it were a pointer. The cast to the (int*)<\/code> involves a reinterpret_cast<\/code> and is horrible. Stick to your first code.<\/p>\n<\/p><\/div>\n
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            8<\/span> <\/p><\/div>\n<\/div>\n
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solved Dereferencing a double-level pointer results in different behaviour from dereferencing a single-level pointer <\/p>\n","protected":false},"excerpt":{"rendered":"
[ad_1] They are very different things. An int** is a pointer to a pointer to an int. If you dereference it, you get an int*. An int* is a pointer to an int. If you dereference it, you get an int. In the first example, you pass an int** with value 0x4df73c as the first … Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[320],"tags":[324,5207,712,4009],"class_list":["post-24621","post","type-post","status-publish","format-standard","hentry","category-solved","tag-c","tag-memory-editing","tag-pointers","tag-reverse-engineering"],"yoast_head":"\n[Solved] Dereferencing a double-level pointer results in different behaviour from dereferencing a single-level pointer - JassWeb<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/jassweb.com\/solved\/solved-dereferencing-a-double-level-pointer-results-in-different-behaviour-from-dereferencing-a-single-level-pointer\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"[Solved] Dereferencing a double-level pointer results in different behaviour from dereferencing a single-level pointer - JassWeb\" \/>\n<meta property=\"og:description\" content=\"[ad_1] They are very different things. An int** is a pointer to a pointer to an int. If you dereference it, you get an int*. An int* is a pointer to an int. If you dereference it, you get an int. In the first example, you pass an int** with value 0x4df73c as the first ... 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