malloc and sizeof question

[cus]

Hi all,

ptr = malloc(number*sizeof(int));

I am using the following line to allocate memory - I understand that malloc requires an integer value as its arguement. In the example above the variable 'number', will be a integer that is entered by the user in order to specify how many integers they want to create in an array. I can see from the statement that the value of 'number' will be multiplied by 'sizeof(int)'.

My question is this, Is there a default value of 'sizeof' that is being used to multiply with the variable 'number', because i don't not understand what is being multiplied.

i.e. if the user enters '5', then..... 5 * sizeof. So whats the value of 'sizeof'.?

[Elysia]

sizeof returns the size of the expression you put inside it.
Since you want to allocate space for n integers, you multiply by the size of an integer, since malloc works with bytes, not elements, and an integer is not merely 1 byte.

[cus]

explained everything thank you, so the end result will consequently be the required amount of space in bytes and so on.

[Elysia]

Yes.

[kermit]

As an aside, you (i.e., cus) may find this FAQ useful as well.