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how to find the length of an array in c/c++ ?

Started by Liam78 Aug 31, 2005 at 7:06 PM 13 replies 78.5k views

Original Post

Aug 31, 2005 at 7:06 PM

hi all I was wondering if there is a way to find out the length of an array in c or c++ for example: char *animals[] = {"cat", "dog", "mouse", "elephant, "rhino", "snake", "fish"}; is there a function that would return to me the number of animals that are stored in this array? In flash for example it would be something like: int num_of_animals = animals.length(); ======================================================== ALso is there a way i can find all the functions that my complier has? for example: printf() scanf() etc,,, will it be in a help file?! i am using bloodched Dev-C++ thx Li

SiCrane

Aug 31, 2005 at 7:10 PM

For a statically allocated array you can use number_of_elements = sizeof(array)/sizeof(type_of_array); In your example: number_of_animals = sizeof(animals)/sizeof(char *).

For dynamic arrays, you either need to store the number yourself or use a class like std::vector.

nilkn

Aug 31, 2005 at 7:12 PM

You can, however, use the SC++L containers, such as std::vector and std::list. [smile]

Quote:

ALso is there a way i can find all the functions that my complier has? for example:
printf()
scanf()
etc,,, will it be in a help file?! i am using bloodched Dev-C++

It's very unlikely the compiler comes with such a list (I've never used bloodshed, so I'm not totally certain, but fairly confident).

There is, however, a plethora of online sources, such as MSDN.

tychon

Aug 31, 2005 at 7:20 PM

In addition to the MSDN, I'd recommend taking a look at cppreference.com.

Liam78

Aug 31, 2005 at 7:25 PM

thankyou for the quick responses people,

appreciated

Li

mozie

Sep 1, 2005 at 9:15 AM

Here is a little sample of how you could use the vector like SiCrane mentioned.

#include<vector>#include<string>int main(){	std::vector< std::string > Animals;	Animals.push_back("cat");	Animals.push_back("dog");	Animals.push_back("mouse");	Animals.push_back("elephant");	Animals.push_back("rhino");	Animals.push_back("snake");	Animals.push_back("fish");	int sz = Animals.size();	std::cout << sz << std::endl;	std::vector< std::string >::iterator b = Animals.begin();	std::vector< std::string >::iterator e = Animals.end();	while(b != e)	{		std::string name = *b;		std::cout << name << std::endl;		++b;	}	system("pause");	return 0;}

You can also treat the vector<> like an array with Animals, but I feel like you loose some of the functionality built into vector working like that.

Zaris

Sep 1, 2005 at 12:24 PM

if you assign the iterators like that does it change with the vector; If I put iter = .end() would it still point to the end when I add items.

perfectly_dark

Sep 1, 2005 at 12:55 PM

Quote:
Original post by Zaris
if you assign the iterators like that does it change with the vector; If I put iter = .end() would it still point to the end when I add items.

I think .end() will ALWAYS point to the last element, no matter how you added it.

nprz

Sep 1, 2005 at 1:00 PM

Quote:
Original post by perfectly_dark
Quote:
Original post by Zaris
if you assign the iterators like that does it change with the vector; If I put iter = .end() would it still point to the end when I add items.

I think .end() will ALWAYS point to the last element, no matter how you added it.

It usually points to 1 past the last element. Otherwise when you loop until end() you will stop before actually using the last element.

Oluseyi

Sep 1, 2005 at 1:02 PM

Quote:
Original post by Zaris
if you assign the iterators like that does it change with the vector; If I put iter = .end() would it still point to the end when I add items.

No, it won't.

SiCrane

Sep 1, 2005 at 2:46 PM

end() is like any iterator into a vector, it can be invalidated through the use of member functions on the vector. In a nutshell, anything that adds or deletes elements to the vector will invalidate end().

benryves

Sep 13, 2005 at 8:11 AM

I'm assuming that the number of elements returned is the upper bound of the array in that case - it returns the index of the last element.
So,
char *animals[] = {"cat", "dog", "mouse", "elephant, "rhino", "snake", "fish"};
...would have a returned count of 6, as element #6 is the last one (0="cat", 1="dog", 2="mouse"... and so on).

Zahlman

Sep 13, 2005 at 11:17 AM

No, the number of elements (as determined for example by a sizeof trick) is the number of elements. Indices range from 0 to n-1 inclusive. It's not that hard to remember and it really, really is handy behaviour.

Iftah

Sep 13, 2005 at 11:29 AM

Quote:
Original post by SiCrane
For a statically allocated array you can use number_of_elements = sizeof(array)/sizeof(type_of_array); In your example: number_of_animals = sizeof(animals)/sizeof(char *).

a more generic approch is using a macro (yuck, i know)
(works only for static allocated)

#define ELEMENT_NUM(_array) (sizeof(_array)/sizeof(_array[0]))

Iftah.

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