file read -- increase the size of an array

[Sameer]

Hello,

i wish to read a file of int and store into an array dynamically...
the size of memory allocated finally, should just be sufficeient to store n
integers.
I do not know the number of integers in the file...
How should I go about creating the array int array[n] dynamically ?

the file is

1
2
3
4
5
...
....
....
....

so on upto n
Kindly reply soon,

Sameer.

[Sameer]

"Sameer" <ia*******@hotm ail.com> wrote in message
news:bk******** ****@ID-160782.news.uni-berlin.de...

Hello,

i wish to read a file of int and store into an array dynamically...
the size of memory allocated finally, should just be sufficeient to store n integers.
I do not know the number of integers in the file...
How should I go about creating the array int array[n] dynamically ?

the file is

1
2
3
4
5
..
...
...
...

so on upto n
Kindly reply soon,

Sameer.

#include<stdio. h>
main()
{
int i=0,j=0,k,num,n ;
int* a;
FILE *fp;
fp=fopen("input " ,"r");

while(fscanf(fp ,"%d", &num)!=EOF)
{
i++;
}

a=new int[i];

for(k=0;k<i;k++ )
{
a[k]=0;
}
fclose(fp);
fp=fopen("input " ,"r");
while(fscanf(fp ,"%d", &num)!=EOF)
{
a[j]=num;
j++;
}

for(k=0;k<i;k++ )
{
printf("%d\n", a[k]);
}
//free a[n];

fclose(fp);
return 0;
}
Here is one way ...but I am reading the files twice ...
By reading the file only once ...is it possible ?

[Irrwahn Grausewitz]

"Sameer" <ia*******@hotm ail.com> wrote:

"Sameer" <ia*******@hotm ail.com> wrote in message
news:bk******* *****@ID-160782.news.uni-berlin.de...

Hello,

i wish to read a file of int and store into an array dynamically...
the size of memory allocated finally, should just be sufficeient to storen

integers.
I do not know the number of integers in the file...
How should I go about creating the array int array[n] dynamically ?

<SNIP>#include<stdio .h>
main()
{
int i=0,j=0,k,num,n ;
int* a;
FILE *fp;
fp=fopen("inpu t" ,"r");

while(fscanf(fp ,"%d", &num)!=EOF)
{
i++;
}

a=new int[i];

^^^

This is not a C program.

My suggestion: use malloc() or realloc() to dynamically grow your
'array' as you go. This way you have to go through your file only
once.

<SNIP>

Regards

Irrwahn
--
What does this red button do?

[Christopher Benson-Manica]

Irrwahn Grausewitz <ir*****@freene t.de> spoke thus:

My suggestion: use malloc() or realloc() to dynamically grow your
'array' as you go. This way you have to go through your file only
once.

My question is, is it more efficient to call realloc() for every integer, or
to go through the file twice and call malloc() only once?

--
Christopher Benson-Manica | Jumonji giri, for honour.
ataru(at)cybers pace.org |

[Thomas Matthews]

Christopher Benson-Manica wrote:

Irrwahn Grausewitz <ir*****@freene t.de> spoke thus:

My suggestion: use malloc() or realloc() to dynamically grow your
'array' as you go. This way you have to go through your file only
once.

My question is, is it more efficient to call realloc() for every integer, or
to go through the file twice and call malloc() only once?

You want to reduce the number of reallocations while not over allocating
memory. Choose a number as an increase amount. When the array is full,
allocate space for another N integers.

Perhaps you want to use a dynamic data structure, such as a linked list.

--
Thomas Matthews

C++ newsgroup welcome message:
http://www.slack.net/~shiva/welcome.txt
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http://www.raos.demon.uk/acllc-c++/faq.html
Other sites:
http://www.josuttis.com -- C++ STL Library book
http://www.sgi.com/tech/stl -- Standard Template Library

[Irrwahn Grausewitz]

Christopher Benson-Manica <at***@nospam.c yberspace.org> wrote:

Irrwahn Grausewitz <ir*****@freene t.de> spoke thus:

My suggestion: use malloc() or realloc() to dynamically grow your
'array' as you go. This way you have to go through your file only
once.

My question is, is it more efficient to call realloc() for every integer, or
to go through the file twice and call malloc() only once?

Depends. Personally, I would choose a third option: realloc() memory
in reasonable big chunks, and when done reading do a last realloc() to
shrink-to-fit (if that is necessary at all, alas the OP's assignment
said so).

Regards,

Irrwahn
--
What does this red button do?

[Christopher Benson-Manica]

Thomas Matthews <Th************ *************** *@sbcglobal.net > spoke thus:

Perhaps you want to use a dynamic data structure, such as a linked list.

Is that a preferred solution?

--
Christopher Benson-Manica | Jumonji giri, for honour.
ataru(at)cybers pace.org |

[Al Bowers]

Christopher Benson-Manica wrote:

Irrwahn Grausewitz <ir*****@freene t.de> spoke thus:

My suggestion: use malloc() or realloc() to dynamically grow your
'array' as you go. This way you have to go through your file only
once.

My question is, is it more efficient to call realloc() for every integer, or
to go through the file twice and call malloc() only once?

I would not go through the file twice and I would use function realloc.
Instead of reallocating on every int read from the file, I would
in blocks. For example you can set the reallocations after every five
integers read. Define BLOCK to whatever value is most efficient for your
requirements.

#define BLOCK 5

int *iarray,num;
unsigned count;
FILE *fp;

/* open the file for reading */
for(iarray = NULL, count = 0U;
EOF != fscanf(fp,"%d", &num);count+ +)
{
int *tmp;
if(count%BLOCK == 0U)
if((tmp = realloc(iarray, (sizeof *iarray)*(count +BLOCK)))
== NULL) break;
iarray = tmp;
iarray[count] = num;
}
--
Al Bowers
Tampa, Fl USA
mailto: xa*@abowers.com base.com (remove the x)
http://www.geocities.com/abowers822/

[Irrwahn Grausewitz]

Christopher Benson-Manica <at***@nospam.c yberspace.org> wrote:

Thomas Matthews <Th************ *************** *@sbcglobal.net > spoke thus:

Perhaps you want to use a dynamic data structure, such as a linked list.

Is that a preferred solution?

Maybe not when dealing with integer items, but of course it is worth
consideration when handling more complex data structures.

Regards

Irrwahn
--
What does this red button do?

[Matt Gregory]

Irrwahn Grausewitz wrote:

Christopher Benson-Manica <at***@nospam.c yberspace.org> wrote:

My question is, is it more efficient to call realloc() for every integer, or
to go through the file twice and call malloc() only once?

Depends. Personally, I would choose a third option: realloc() memory
in reasonable big chunks, and when done reading do a last realloc() to
shrink-to-fit (if that is necessary at all, alas the OP's assignment
said so).

Is it really that big of a deal to call realloc() every time? Doesn't
realloc() get memory in semi-big blocks anyway? Is it worth the added
complexity to manage the blocks ourselves?

Matt Gregory