How do we get the number of elements in an array without using sizeof

Question

How do we get the number of elements in an arraywithout using sizeof. In any case sizeof does not get me the correct number of elemnts so I want to implement my self without using sizeof.

I tried to run using sizeof and it doesn't print the correct number of elements in an array.

int n = sizeof(arr) / sizeof(arr[0]);
for (int i = 0; i < n; i++){
printf("%s\n", arr[i]);
}   
// to check if the noof elts in the arr is correct 
printf("%d\n", n);

You can't do that. What is `arr` in your example? The code in your question looks OK to me, provided `arr` is actually an array like `int arr[10]`. Don't describe it, but [edit] mand add the corrresponding declaration. Also read this [mcve]. — Jabberwocky, Jan 11 '22 at 11:28
Please [edit] your question and create a [mre], i.e some example code we can compile and run which demonstrates a case where `sizeof` does not work as you expect. My guess is that you pass an array to a function and try to use `sizeof` inside the called function. — Bodo, Jan 11 '22 at 11:30
If `arr` is a parameter of a function, it is never an array but decays to a pointer. In that case `sizeof` will not work for you. — Gerhardh, Jan 11 '22 at 11:30
[`sizeof` isn't a function but an operator](https://stackoverflow.com/q/1393582/995714) because you can use `sizeof x` without parentheses — phuclv, Jan 11 '22 at 11:31
@Yemi Bold If the character array contains a string then use the function strlen. — Vlad from Moscow, Jan 11 '22 at 11:35
Does this answer your question? [Determine size of dynamically allocated memory in C](https://stackoverflow.com/questions/1281686/determine-size-of-dynamically-allocated-memory-in-c) — Karol T., Jan 11 '22 at 11:40

score 1 · Answer 1 · answered Jan 11 '22 at 11:35

When you use an array as an argument in a function call, it is automatically converted to a pointer to its first element. The C standard does not provide any means for finding the size of an array given only a pointer to its first element.

For a function to know the size of an array that is passed to it in this way, you must pass the size as a separate argument or must provide the function some other way of knowing the size, such as including a sentinel value to mark the end. (For example, the null character that marks the end of a string is a sentinel.)

How do we get the number of elements in an array without using sizeof

1 Answers1