How can get on the number of elements dynamic array

[mercala_eng]

I declared the array in this way:

int *KeyValue=(int*)malloc(100*sizeof(int)); 

for(int i; ;){
     KeyValue[i] =  it->first * it->second ; u++;
   }

After using the KeyValue[] array I need to know the size of this array to used it in another place in my code.
I used something like this but this return just 1;
int sizeKeyValue =sizeof(KeyValue)/sizeof(KeyValue[0]);

How can I get the number of elements in dynamic array?

[gcjr]

@mercala_eng

How can I get the size of dynamic array?

you specified it

@mercala_eng

100*sizeof(int)

[b707]

@mercala_eng

How can I get the size of dynamic array?

You must remember it when creating an array.

Do not use "magic numbers" for size, use macros or constexpr for it:

@mercala_eng

#define KEY_ARRAY_SIZE 100
int *KeyValue=(int*)malloc(KEY_ARRAY_SIZE*sizeof(int)); `

so
int sizeKeyValue = KEY_ARRAY_SIZE;

[awneil]

You know the size - because you defined it in the malloc call!

Instead of using a Magic Number like 100, make that a symbolic value that you can pass to these other places.

Or do you mean, how to know how many elements of the array have actually been "used" or "filled"?

To know that, you could:

1. Keep a count as you use elements;
2. Have a specific value to indicate the end of "used" data (as in C strings)

[UKHeliBob]

@mercala_eng

How can I get the size of dynamic array?

Do you mean that you want to know how many entries the array can hold or perhaps how many entries have been placed in the array ?

Either way the array size is not dynamic

[mercala_eng]

But I did not use all the size, I used just 10. Is there any know the number of values in the dynamic array?

[awneil]

yes:

@awneil

1. Keep a count as you use elements;
2. Have a specific value to indicate the end of "used" data (as in C strings)

[b707]

@mercala_eng

But I did not use all the size, I used just 10. Is there any know the number of values

It seems an absolutely different problem rather than stated in the topic title.

[mercala_eng]

Yes, I mean that, I am asking is there any way to know the number of elements in the dynamic array without using a counter ?

[awneil]

@mercala_eng

Yes, I mean that

It's not what you said!

You understand that the size of the array - ie, the amount of memory that it occupies - does not change?

@mercala_eng

is there any way to know the number of elements in the dynamic array

Again, the number of elements does not change - it's just a matter of whether you've written anything to them or not

without using a counter ?

Yes - I gave you a 2nd way!

[mercala_eng]

Can you give an example for the 2nd way please?

[awneil]

@mercala_eng

#define ARRAY_SIZE  100
#define EMPTY_VALUE 0

int *array=(int*)malloc( ARRAY_SIZE*sizeof(int) ); 

memset( array, EMPTY_VALUE, ARRAY_SIZE );

Now you can just loop through the array until you find an element containing EMPTY_VALUE.

You have to choose an EMPTY_VALUE that can never be used as an actual data value.

https://cplusplus.com/reference/cstring/memset/

[mercala_eng]

Thanks!

[awneil]

Maybe one of these Container Classes could help:

GitHub - hideakitai/ArxContainer: C++ container-like classes (vector, map,...

[gcjr]

@mercala_eng

int sizeKeyValue =sizeof(KeyValue)/sizeof(KeyValue[0]);

sizeof() is used at compilation time knowing that size of the variable that's been allocated.

@mercala_eng

for(int i; ;){
     KeyValue[i] =  it->first * it->second ; u++;
   }

what stops this loop from running forever?

[Budvar10]

@gcjr

what stops this loop from running forever?

It was probably meant as a sketch, i has not defined value.