How to find length of char** ?

harely9 · 05-22-2018, 04:45 AM

I tried this

Code:

sizeof(char) / sizeof(char[0])

but it always returns 1

rtmistler · 05-22-2018, 06:52 AM

It seems very unclear what you're asking.

Please consider being more clear with your question, or providing more background about what you are looking to determine.

Your thread title and your code are different.

First off, the sizeof(char) is whatever the machine decides, but likely it is 1.

Divide that by the sizeof a zero element array and I'm unsure why you didn't get a "divide by zero" exception in your program. Unless the compiler implicitly made that a single character, where then it decided that anything divided by the same thing is always 1.

The length of a pointer is the natural length of a register on the machine you are using.

If you want the length of the pointer, then use sizeof(char *)

harely9 · 05-22-2018, 09:31 AM

I have dynamically assigned an array of strings. I try to find a length of array, which means how many strings there are in the array.
and i dont want to count

rtmistler · 05-22-2018, 09:49 AM

Quote:

Originally Posted by harely9

I have dynamically assigned an array of strings. I try to find a length of array, which means how many strings there are in the array.
and i dont want to count

Taking that comment as literal.

This would therefore not be about memory size, but instead the literal count of strings you have added to this array.

Your code would have to count.

As you add strings to the array, you just bump the count of strings variable up by 1 each time.

If you add some huge chunk, or multiple huge chunks, either each chunk counts as 1, or you need to search each chunk to derive the number of strings included, such as search for newline characters and count them.

Or ...

Do you really mean that you want the entire size of this large array you have built up?

There are a number of ways to build an array of strings, you could have pre-allocated a static memory chunk, you could be building it up piece by piece as you get new strings.

Can you post a representative code clip which illustrates how you are building this array?

NevemTeve · 05-22-2018, 03:09 PM

@OP: use a variable to store the number of used elements:

Code:

int used= 0;
int total= 0;
char **ptr= NULL;
...
if (used==total) {
    total+=10;
    ptr= realloc (ptr, total*sizeof(char *));
}
ptr[used]= strdup(input);
++used;

Jerry Mcguire · 06-15-2018, 01:31 PM

It does not work like that as sizeof pointer over size of pointer is of course always 1.

I suppose you saw the sizeof(something)/sizeof(something[0]) somewhere which can help you access the max number items in that array. It only works when the type size is known at compile time.

Code:

  item_t item[360];

...

  size_t max_size = sizeof(item)/sizeof(item[0]); /* yields 360 */

If your array is dynamic, then you will have to keep count.

Also, char** is not array of string. It is pointer to pointer to char (or handle to char).

pan64 · 06-15-2018, 02:12 PM

Quote:

Originally Posted by harely9

I have dynamically assigned an array of strings. I try to find a length of array, which means how many strings there are in the array.
and i dont want to count

Actually I do not understand you. You either need to store the length of the array somewhere or count it. I couldn't imagine any other way.
So if you have it somewhere just use, otherwise count it.
Since you gave no information about how it was created/constructed hard to say more, but probably there are some tricks....

rtmistler · 06-15-2018, 02:19 PM

Well it's kind of a half month old question where the OP didn't clarify or post any representative code.