Array size

[BrianJones]

In java, to work out the size of an array, say it was called a, you would do
a.length which might return 10 as the number of elements.

Is there a similar thing you can do in C++? I'd initially thought of using
strlen(a) since the array I am working with is of type char. However, I
found this to return a value drastically smaller than the number of elements
it actually contained

Thanks
Ben

[Ioannis Vranos]

BrianJones wrote:

In java, to work out the size of an array, say it was called a, you would do
a.length which might return 10 as the number of elements.

Is there a similar thing you can do in C++? I'd initially thought of using
strlen(a) since the array I am working with is of type char. However, I
found this to return a value drastically smaller than the number of elements
it actually contained

Not for built in arrays. You must use standard library containers like
vector that have a size() member function. Also for regular applications
you should use standard library containers anyway and do not bother
yourself with low level stuff.


Regards,

Ioannis Vranos

http://www23.brinkster.com/noicys

[Gianni Mariani]

BrianJones wrote:

In java, to work out the size of an array, say it was called a, you would do
a.length which might return 10 as the number of elements.

Is there a similar thing you can do in C++? I'd initially thought of using
strlen(a) since the array I am working with is of type char. However, I
found this to return a value drastically smaller than the number of elements
it actually contained

If you have the definition of the array handy you can do this:
template <typename T, unsigned N>
inline unsigned Length( T (&x)[N] )
{
return N;
}

int Array[ 230 ];
extern int ExternArray[]; // don't know the length

#include <iostream>

int main()
{
std::cout << Length( Array ) << "\n";
std::cout << Length( ExternArray ) << "\n"; // error
}

If you pass around arrays and you need the length, then std::vector is
the way to go.

[Jacek Dziedzic]

BrianJones wrote:

[...]
I'd initially thought of using
strlen(a) since the array I am working with is of type char. However, I
found this to return a value drastically smaller than the number of elements
it actually contained

Perhaps you have the character '\0' inside your array of chars.
It servers as an end-of-string marker for strlen().

hth,
- J.

[Arijit]

"BrianJones" <br***@jones1611.fsnet.co.uk> wrote in message news:<cc**********@news6.svr.pol.co.uk>...

In java, to work out the size of an array, say it was called a, you would do
a.length which might return 10 as the number of elements.

Is there a similar thing you can do in C++? I'd initially thought of using
strlen(a) since the array I am working with is of type char. However, I
found this to return a value drastically smaller than the number of elements
it actually contained

Thanks
Ben

C style strings are terminated by a null character,'\0'. strlen
actually checks the position of this '\0'. If your array contains
no '\0',using strlen can actually cause your program to crash. As a
hack, you might consider placing a sentinel '\0' at the end of the array.
Then strlen will return the size of the array - 1. But you should really
consider using a vector.

-Arijit

[Arijit]

"BrianJones" <br***@jones1611.fsnet.co.uk> wrote in message news:<cc**********@news6.svr.pol.co.uk>...

In java, to work out the size of an array, say it was called a, you would do
a.length which might return 10 as the number of elements.

Is there a similar thing you can do in C++? I'd initially thought of using
strlen(a) since the array I am working with is of type char. However, I
found this to return a value drastically smaller than the number of elements
it actually contained

Thanks
Ben

C style strings are terminated by a null character,'\0'. strlen
actually checks the position of this '\0'. If your array contains
no '\0',using strlen can actually cause your program to crash. As a
hack, you might consider placing a sentinel '\0' at the end of the array.
Then strlen will return the size of the array - 1. But you should really
consider using a vector.

-Arijit

[Anonymous]

You should be using vector in those cases. Your program will work as per the
suggestions, but when you have store other objects, there wont be any way for
you to get the size unless you keep a track of the things put in the array.
Using vector is more "C++ way",compared to the "C" way you are doing.

--
Use our news server 'news.foorum.com' from anywhere.
More details at: http://nnrpinfo.go.foorum.com/

[Thomas Matthews]

BrianJones wrote:

In java, to work out the size of an array, say it was called a, you would do
a.length which might return 10 as the number of elements.

Is there a similar thing you can do in C++? I'd initially thought of using
strlen(a) since the array I am working with is of type char. However, I
found this to return a value drastically smaller than the number of elements
it actually contained

Thanks
Ben

Here are some general guidelines:
1. When working with a collection of characters,
prefer std::string to char * or char [].

2. Prefer std::vector to an array.

3. Length of a string is different than the length
of an array (or the capacity of the container).
I could have the string "Hello" in a container
that has a capacity of 64. The length of the
string is much smaller than the capacity of
the container.

4. The language does not know the length of an
array that a pointer points to.

5. When storing strings to a file, decide whether
you want to specify length then text or text
terminated by a sentinel value.

6. Read the FAQ. Understand the FAQ. Read the
FAQ for the C language as well.

--
Thomas Matthews

C++ newsgroup welcome message:
http://www.slack.net/~shiva/welcome.txt
C++ Faq: http://www.parashift.com/c++-faq-lite
C Faq: http://www.eskimo.com/~scs/c-faq/top.html
alt.comp.lang.learn.c-c++ faq:
http://www.raos.demon.uk/acllc-c++/faq.html
Other sites:
http://www.josuttis.com -- C++ STL Library book