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| Original file line number | Diff line number | Diff line change |
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| <!-- other --> | ||
| <!doctype html> | ||
| <html lang="en"> | ||
| <head> | ||
| <meta charset="utf-8"> | ||
| <title>other example</title> | ||
| <meta content="width=device-width,initial-scale=1,user-scalable=no" name=viewport> | ||
| <script src="style.js" defer></script> | ||
| </head><body> | ||
| This is a tricky thing to grok at first, so i'll try to illustrate it like this... | ||
| Now, hopefully you already read and learned about how the dot & arrow operators | ||
| work as pointers... | ||
| Consider we have this sortve structure... | ||
| <span class="alt-text"> | ||
| typedef struct { | ||
| char *buffer; | ||
| } Anar; | ||
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| typedef struct { | ||
| Anar nar; | ||
| } Vac; | ||
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| typedef struct { | ||
| Vac *pack; | ||
| } Database;</span> | ||
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| `Anar` contains a single member, `buffer`, which is a pointer to a character array. | ||
| `Vac` contains a single member, `nar`, which is of type `Anar`. | ||
| `Database` contains a single member, `pack`, which is a pointer to a `Vac`. | ||
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| To access the buffer member of `Anar` (which is nested within `Vac`) and then within Database, | ||
| you need to handle the pointers and structs in the right way.... | ||
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| Consider we have a `database` which is a pointer to a Database struct, possibly like this... | ||
| <span class="alt-text"> | ||
| Database *database = (Database *)malloc(sizeof(Database)); | ||
| if (database == NULL) { | ||
| perror("Failed to allocate memory for Database"); | ||
| return 1; | ||
| }</span> | ||
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| Which is for allocating and initializing a `Database` instance. Here's some things we might do... | ||
| `database->pack` accesses the `pack` member of `Database`, which is a pointer to a `Vac` struct. | ||
| `*database->pack` would dereference the pointer, yielding the actual `Vac` struct. | ||
| `(*database->pack).nar` would access the `nar` member of the `Vac` struct. | ||
| `(*database->pack).nar.buffer` accesses the `buffer` member of the `Anar` struct. | ||
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| It sounds more complicated than it is, since its describing multiple scenarios, however you can | ||
| take it from the last scenario, and sortve trace the steps backwards so to speak... | ||
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| The last scenario, we said we could take that `(*database>pack)` to access the `buffer` member of the `Anar` struct. | ||
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| In C, when you mix (.) period and (->) arrow operators with dereferencing, parentheses adheres the order of | ||
| operations. Without parentheses, you can’t directly use the (.) operator on a pointer without first dereferencing it. | ||
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| For example, consider *database->pack.nar.buffer Here’s how the C compiler interprets it: | ||
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| `database->pack` is a pointer to Vac. | ||
| `database->pack.nar` is an invalid syntax because (->) should be used for accessing members from a pointer | ||
| to a struct, and `nar` is not a member of ` Vac * ` but of `Vac` | ||
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| To correctly access buffer, you need to dereference `database->pack` to get the `Vac` struct. | ||
| Access the `nar` member of the `Vac` struct. And access the `buffer` member of the `Anar` struct (as we said when describing the last scenario) | ||
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| So the correct syntax in that particular situation would be: | ||
| <span class="alt-text"> | ||
| (*database->pack).nar.buffer | ||
| </span> | ||
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| At some point you might even consider simplifying access with a temporary variable | ||
| <span class="alt-text"> | ||
| Vac *exac = *database->pack;</span> | ||
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| Which would allow you to use it as `exac->nar.buffer` | ||
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