StackOverflow2013

Note that there are some explanatory texts on larger screens.

plurals

POC pointer address changes without assignment
primarykey
Id
18931349
data
AcceptedAnswerId
0
AnswerCount
2
ClosedDate
CommentCount
9
CommunityOwnedDate
CreationDate
2013-09-21T10:07:15.620
FavoriteCount
0
LastActivityDate
2013-09-21T20:27:37.507
LastEditDate
2013-09-21T10:19:00.827
LastEditorUserId
1790803
OwnerUserId
1790803
ParentId
0
PostTypeId
1
Score
2
ViewCount
1383
LastEditorDisplayName
text
Body
I am working on a Uni assignment here, and I've run into a problem. I am attempting to store a string input at a point inside a struct using a for-loop. Later on I intend to use the pointer to the place where the data was stored to fetch the string. Now the problem is, as I move on inside my for-loop, the address of the point changes as well. This code: <pre><code>printf("B: %p\n", txt->point); for(i = 0; i < input_sz; i++) { txt->point[i] = input[i]; } printf("A: %p\n", txt->point); </code></pre> gives the output: <pre><code>B: 0x7fc111803200 A: 0x7fc111803265 </code></pre> where B is before-value and A is after-copying value. Any help debugging this would be very appreciated! <hr> EDIT: Here's some more code: The struct: <pre><code>struct text_storage { char* start; char* point; char* end; } typedef text_t; </code></pre> Initialization function: <pre><code>text_t* text_init(void *memory, size_t size) { text_t* to_return; if(size < sizeof(text_t)) { return NULL; } to_return = (text_t*) memory; to_return->start = to_return; to_return->end = to_return->start + size; to_return->point = to_return->start; printf("Start: %p, point: %p, end: %p, end-start: %d\n", to_return->start, to_return->point, to_return->end, (to_return->end - to_return->start)); return to_return; } </code></pre> The text-store method in which the error occurs: <pre><code>int text_store_entry(text_t *txt, const char *input, size_t input_sz) { int to_return; char* begin = txt->point; int i; if(input_sz > (txt->end - txt->point)) { return -1; } printf("Start: %p, point: %p, end: %p, end-start: %d\n", txt->start, txt->point, txt->end, (txt->end - txt->start)); printf("B: %p\n", txt->point); for(i = 0; i < input_sz; i++) { txt->point[i] = input[i]; } printf("A: %p\n", txt->point); } </code></pre> Main-function (testing purposes only): <pre><code>int main(int argc, char* argv[]) { void* memory = malloc(10000); char* a = "hei pa deg din trekkbasun"; text_t* txt; int memoverwritten; txt = text_init(memory, 10000); memoverwritten = text_store_entry(txt, a, (size_t)26); printf("got through\n"); return 0; } </code></pre>
Tags
<c><pointers><struct><pointer-arithmetic>
Title
C pointer address changes without assignment
singulars
PostAcceptedAnswerId
1. This table or related slice is empty.
PostParentId
1. This table or related slice is empty.
PostTypePostTypeId
1. PTQuestion
UserLastEditorUserId
1. USHenrik Hillestad Løvold
UserOwnerUserId
1. USHenrik Hillestad Løvold
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
VotesPostIdCreationDate
1. VO
 singulars
 PostPostId
 POC pointer address changes without assignment
 UserUserId
 This table or related slice is empty.
 VoteTypeVoteTypeId
 VTUpMod
CommentsPostId

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.