StackOverflow2013

Note that there are some explanatory texts on larger screens.

plurals

POWhat's the difference between intializating a struct as pointer or not?
primarykey
Id
2335536
data
AcceptedAnswerId
2335872
AnswerCount
5
ClosedDate
CommentCount
0
CommunityOwnedDate
CreationDate
2010-02-25T16:14:21.503
FavoriteCount
0
LastActivityDate
2010-02-25T17:14:09.340
LastEditDate
LastEditorUserId
0
OwnerUserId
40480
ParentId
0
PostTypeId
1
Score
1
ViewCount
802
LastEditorDisplayName
text
Body
I have the following for my HashTable structure: <pre><code>typedef char *HashKey; typedef int HashValue; typedef struct sHashElement { HashKey key; HashValue value; } HashElement; typedef struct sHashTable { HashElement *items; float loadFactor; } HashTable; </code></pre> I never really thought about it until now but I just realized there's two ways how I can use this: Alternative 1: <pre><code>void hashInitialize(HashTable *table, int tabSize) { table->items = malloc(sizeof(HashElement) * tabSize); if(!table->items) { perror("malloc"); exit(1); } table->items[0].key = "AAA"; table->items[0].value = 45; table->items[1].key = "BBB"; table->items[1].value = 82; table->loadFactor = (float)2 / tabSize; } int main(void) { HashTable t1; int i; hashInitialize(&t1, HASHSIZE); for(i = 0; i < HASHSIZE - 1; i++) { printf("PAIR(%d): %s, %d\n", i+1, t1.items[i].key, t1.items[i].value); } printf("LOAD FACTOR: %.2f\n", t1.loadFactor); return 0; } </code></pre> Alternative 2: <pre><code>void hashInitialize(HashTable **table, int tabSize) { *table = malloc(sizeof(HashTable)); if(!*table) { perror("malloc"); exit(1); } (*table)->items = malloc(sizeof(HashElement) * tabSize); if(!(*table)->items) { perror("malloc"); exit(1); } (*table)->items[0].key = "AAA"; (*table)->items[0].value = 45; (*table)->items[1].key = "BBB"; (*table)->items[1].value = 82; (*table)->loadFactor = (float)2 / tabSize; } int main(void) { HashTable *t1 = NULL; int i; hashInitialize(&t1, HASHSIZE); for(i = 0; i < HASHSIZE - 1; i++) { printf("PAIR(%d): %s, %d\n", i+1, t1->items[i].key, t1->items[i].value); } printf("LOAD FACTOR: %.2f\n", t1->loadFactor); return 0; } </code></pre> Question 1: They both seem to produce the same result. On <code>main</code>, both examples print the right key/value pair. So, what exactly is the different between them besides the syntax change (using <code>(*table)</code> instead of just <code>table</code>), the extra code to allocate memory for the <code>HashTable</code> structure and the declaration of <code>HashTable</code> pointer? I've been writing a few data structures lately like stacks, linked lists, binary search trees and now hash tables. And for all of them, I've always used the alternative 2. But now I'm thinking if I could have used alternative 1 and simplify the code, removing most of the <code>*</code> and <code>&</code> that are all over the place. But I'm asking this question to understand the differences between the two methods and if, and also why, I should use on over the other. Question 2: As you can see in the structures code, <code>HashKey</code> is a pointer. However, I'm not using <code>strdup</code> nor <code>malloc</code> to allocate space for that string. How and why is this working? Is this OK to do? I've always used <code>malloc</code> or <code>strdup</code> where appropriate when handling dynamic strings or I would get lots of segmentation faults. But this code is not giving me any segmentation faults and I don't understand why and if I should do it like this.
Tags
<c><memory><pointers><hashtable><structure>
Title
What's the difference between intializating a struct as pointer or not?
singulars
PostAcceptedAnswerId
1. PO
 singulars
 PostTypePostTypeId
 PTAnswer
PostParentId
1. This table or related slice is empty.
PostTypePostTypeId
1. PTQuestion
UserLastEditorUserId
1. This table or related slice is empty.
UserOwnerUserId
1. USRicardo Amaral
plurals
PostLinksPostIdRelatedPostId
1. PL
 singulars
 LinkTypeLinkTypeId
 LTLinked
PostLinksRelatedPostIdPostId
1. This table or related slice is empty.
PostsAcceptedAnswerId
1. This table or related slice is empty.
PostsParentIdCreationDate
1. PO
 singulars
 PostTypePostTypeId
 PTAnswer
2. PO
 singulars
 PostTypePostTypeId
 PTAnswer
3. PO
 singulars
 PostTypePostTypeId
 PTAnswer
VotesPostIdCreationDate
1. VO
 singulars
 PostPostId
 POWhat's the difference between intializating a struct as pointer or not?
 UserUserId
 This table or related slice is empty.
 VoteTypeVoteTypeId
 VTUpMod
CommentsPostId
1. This table or related slice is empty.

Querying!

Guidance

A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.