naive size of array question

[sillyhat]

Hello,

Can someone please help.

I have come across code similar to this which I prepared as an
example:-
/*-------------8<------------------*/
#define ASIZE 10
int main()
{
char *A[] = { "one", "two","three","four","five",
"six","seven","eight","nine","ten" };
int i;

for (i=0; i<ASIZE; i++)
puts(A);

return 0;
}
/*-------------8<------------------*/
and I would like to know how to code this so that ASIZE is calculated
at compile time - by macros perhaps.

Alternatively I could put an empty string in as the last entry and
ignore ASIZE but I wondered if there were other techniques to determine
the number of items in an array with variable length entries like this.

Thanks for any help given.
Hal

 

[Antonio Contreras]

Hello,

Can someone please help.

I have come across code similar to this which I prepared as an
example:-
/*-------------8<------------------*/
#define ASIZE 10
int main()
{
char *A[] = { "one", "two","three","four","five",
"six","seven","eight","nine","ten" };
int i;

for (i=0; i<ASIZE; i++)
puts(A);

return 0;
}
/*-------------8<------------------*/
and I would like to know how to code this so that ASIZE is calculated
at compile time - by macros perhaps.

Alternatively I could put an empty string in as the last entry and
ignore ASIZE but I wondered if there were other techniques to determine
the number of items in an array with variable length entries like this.

Thanks for any help given.
Hal

You can calculate the size with:

sizeof (A) / sizeof (A[0])

HTH

 

[Christopher Benson-Manica]

#define ASIZE 10
int main()
{
char *A[] = { "one", "two","three","four","five",
"six","seven","eight","nine","ten" };
}

and I would like to know how to code this so that ASIZE is calculated
at compile time - by macros perhaps.

You want sizeof A/sizeof *A. No macros are needed.

 

[sillyhat]

Ouch!

It was even more naive than I realised!

Cheers!
Hal

 

[Alf P. Steinbach]

* (e-mail address removed):

I have come across code similar to this which I prepared as an
example:-
/*-------------8<------------------*/
#define ASIZE 10
int main()
{
char *A[] = { "one", "two","three","four","five",
"six","seven","eight","nine","ten" };
int i;

for (i=0; i<ASIZE; i++)
puts(A);

return 0;
}
/*-------------8<------------------*/
and I would like to know how to code this so that ASIZE is calculated
at compile time - by macros perhaps.

Alternatively I could put an empty string in as the last entry and
ignore ASIZE but I wondered if there were other techniques to determine
the number of items in an array with variable length entries like this.

There are five commonly used ways, which differ in what they're good
for.

A very short comparision is provided at
<url:
http://home.no.net/dubjai/win32cpptut/special/pointers/array_size.doc.pdf>.

Hth.,

- Alf

 

[Flash Gordon]

* (e-mail address removed):

I have come across code similar to this which I prepared as an
example:-
/*-------------8<------------------*/
#define ASIZE 10
int main()
{
char *A[] = { "one", "two","three","four","five",
"six","seven","eight","nine","ten" };

There are five commonly used ways, which differ in what they're good
for.

A very short comparision is provided at
<url:
http://home.no.net/dubjai/win32cpptut/special/pointers/array_size.doc.pdf>.

Most of those ways are C++ not C.

 

[Alf P. Steinbach]

* Flash Gordon:

Most of those ways are C++ not C.

I'm sorry, wrong group.

 

[Mike Wahler]

Hello,

Can someone please help.

I have come across code similar to this which I prepared as an
example:-
/*-------------8<------------------*/
#define ASIZE 10
int main()
{
char *A[] = { "one", "two","three","four","five",
"six","seven","eight","nine","ten" };
int i;

for (i=0; i<ASIZE; i++)
puts(A);

return 0;
}
/*-------------8<------------------*/
and I would like to know how to code this so that ASIZE is calculated
at compile time - by macros perhaps.

That's exactly what you're doing already. The *macro* 'ASIZE'
generates the integer constant value 10 at compile time.

Alternatively I could put an empty string in as the last entry and
ignore ASIZE but I wondered if there were other techniques to determine
the number of items in an array with variable length entries like this.

I think you're asking about determining an array's size at run time,
not compile time.

The size in bytes is:
sizeof A;

The size in elements is:
sizeof A / sizeof *A;

But be warned that this only works in the scope where the array
is defined. Passed to a function, an array's name is converted
to a pointer to the first element, so sizeof will give the pointer's
size, not the array's size.

-Mike