char *p;
fgets(p,10,stdin);
Why is this crashing my program? Seems like I can't use char pointers in Fgets but I can use arrays so it makes no sense.
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1char pointers are not arrays.Martin James– Martin James2016-03-27 20:36:07 +00:00Commented Mar 27, 2016 at 20:36
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To start with, they have to point to something valid before you dereference them, eg. try to write through them.Martin James– Martin James2016-03-27 20:36:49 +00:00Commented Mar 27, 2016 at 20:36
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Really? Guess my understanding is weak then. I read that arrays are just pointers.chickenman– chickenman2016-03-27 20:37:07 +00:00Commented Mar 27, 2016 at 20:37
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If you read that on a site, delete the bookmark and/or history. If it's in a paper book, apply gasoline and a match.Martin James– Martin James2016-03-27 20:38:21 +00:00Commented Mar 27, 2016 at 20:38
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@MartinJames we don't need anymore global warming. A shredder will do just fine. :PSourav Ghosh– Sourav Ghosh2016-03-27 20:39:30 +00:00Commented Mar 27, 2016 at 20:39
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1 Answer
Seems like I can't use char pointers in Fgets but I can use arrays
No, you can use both, as long as you allocate memory to the pointer before passing that to fgets().
In this case, using pointers,
char *p;
p is unitialized and points to some arbitrary memory location which is invalid. You need to allocate proper memory to p before you can read/write something to/from the memory location pointer by p.
7 Comments
chickenman
How do I know how much memory I give to p if I don't know the input length from the user?
Sourav Ghosh
@qaispak You must be knowing the length, otherwise how do you suggest the array worked?
chickenman
Sorry, by that I actually meant: "The array (when I know the length), I can get input but I want to know how to get it if I don't know the length... which I assumed is when we use pointers (but I am wrong since we need to define length for pointers as well)
Sourav Ghosh
@qaispak yes,
fgets() wont allocate memory to the pointer. You need to allocate memory prior to passing the pointer.chickenman
Yes I understand that, but how do I know how much memory to allocate?
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