Malloc and arrays

Question

I want to create an array of 100 words and each word has 10 max characters but I also want to save in a variable the number of words in this array.

char array[1000];

Is this the most efficient way or can I use malloc() like this:

char *k;
k=(char *)malloc(1000 * sizeof(char));

How can I accomplish my task?

@Χάρης Τουλούπας in C there is no need to cast malloc because of its return type which is **void***. If you get some errors you are probably use a wrong compiler. — Michi, Sep 24 '15 at 22:44
You also should make room for a null terminating character so the above should be `char array[100][11];` — Cyclonecode, Sep 24 '15 at 22:44
"to create an array of 100 words...I also want to save in a variable the number of words". I'm confused. You want to store 100 words or a variable number of words? — Paul92, Sep 24 '15 at 22:44
My advice: erase the word "efficiency" from your vocabulary and your thought process for.. say for a year...at least. Learn the language first. — Karoly Horvath, Sep 24 '15 at 22:44
I'm very confident most C books have a very similar example. — too honest for this site, Sep 24 '15 at 22:45
*efficient* has two orthogonal dimensions: space and time. If talking about efficiency, most of the time you have to find a trade-off between memory efficiency and runtime performance. In theory, with your data you could be more memory efficient using some dynamic allocation (not like your code which would still allocate the whole 1000 bytes) but pay for it with the cost of the `malloc()` and `free()` execution. — , Sep 24 '15 at 22:49

score 2 · Answer 1 · answered Sep 24 '15 at 22:52

If you have an array of 100 words, perhaps you better use 2 dimesional array, like char array[100][11]. I'm specifying the second dimension as 11 because I'm taking into the consideration the null character (a word with max 10 chars + 1 null), the majority of string handling functions in C expect the strings to be null terminated.

score 1 · Answer 2 · edited May 23 '17 at 11:58

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it depends on how you want to use the stored data. What is its lifetime?

your first one is ambiguous:

char array[1000] outside a function is static data; inside a function its on the stack

the second one puts it on the heap.

You should read up on the differences between the characteristics of these 3 different allocation types (they all have pluses and minuses)

Stack, Static, and Heap in C++ is one place

edited May 23 '17 at 11:58

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answered Sep 24 '15 at 22:45

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He Tagged **C**, and as i know the standard doesn't say something about Stack or Heap. – Michi Sep 24 '15 at 22:49
Section 6.2.4 speaks only about **storage durations for objects** – Michi Sep 24 '15 at 22:51

score 1 · Answer 3 · answered Sep 24 '15 at 22:45

In general, if you're looking for performance the declaration of char array[1000] is going to win because it's allocated on the stack.

When you allocate memory using malloc, it's coming from the heap. Also, it's good practice to always do static allocation if you can get away with it because it drastically reduces your chances of a memory leak, the memory will automatically be freed when you leave the scope.

Malloc and arrays

3 Answers3