[c] How do I find the length/number of items present for an array?

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length of array in function argument

My array size is 5. For example:

arrCustId[5]

How can I know how many Customer IDs are already present in my array? In short how to find length of array?

This question is related to c arrays

The answer is


If the array is statically allocated, use sizeof(array) / sizeof(array[0])

If it's dynamically allocated, though, unfortunately you're out of luck as this trick will always return sizeof(pointer_type)/sizeof(array[0]) (which will be 4 on a 32 bit system with char*s) You could either a) keep a #define (or const) constant, or b) keep a variable, however.


Do you mean how long is the array itself, or how many customerids are in it?

Because the answer to the first question is easy: 5 (or if you don't want to hard-code it, Ben Stott's answer).

But the answer to the other question cannot be automatically determined. Presumably you have allocated an array of length 5, but will initially have 0 customer IDs in there, and will put them in one at a time, and your question is, "how many customer IDs have I put into the array?"

C can't tell you this. You will need to keep a separate variable, int numCustIds (for example). Every time you put a customer ID into the array, increment that variable. Then you can tell how many you have put in.


I'm not sure that i know exactly what you mean.

But to get the length of an initialized array,

doesn't strlen(string) work ??