problem with fread function

nesta · 04-02-2007, 07:19 AM

hi all,
i have a txt file named by hello.txt
i wanna read the file untill the end of it.

i write the following simple code :

Code:

#include <stdio.h>

char outbuff[7*1024];

int main ()
{
	int read_bytes,fd,write_bytes;

	printf("Start reading data\n");
	fd  = fopen("hello.txt","r");
	if (fd==NULL)
		printf("error cant open the file\n");
	read_bytes = fread(outbuff, sizeof(outbuff), 1,fd);
	printf("the read bytes ar %d\n",read_bytes);
	fclose(fd);
         return 0;
}

when i run the previous program, the read_bytes variable was zero.
and also i dont know how can i read the file till the end. alll i just can imagine is that i should make a while loop?
can anyone help me please, thanks in advance

ntubski · 04-02-2007, 08:50 AM

first of all fd should be a FILE* not an int, that should get rid of a whole bunch of compile warnings

Quote:

Originally Posted by man fread

size_t fread(void *ptr, size_t size, size_t nmemb, FILE *stream);

The function fread() reads nmemb elements of data, each size bytes
long, from the stream pointed to by stream, storing them at the loca-
tion given by ptr.

It looks to me like to you mixed up the size and nmemb parameters, when I switch them your program works. I think what was happening was that fread didn't manage to get a whole "element" of size 7*1024, so it just returned without reading anything.

jim mcnamara · 04-02-2007, 08:51 AM

I do not see how it compiled in the first place.
Remove fd from the list of int's you declared.
Add this line as a declaration:
FILE *fd=NULL;

Also whenever you open a file, check the returns - ie., if(fd==NULL) { report the error }

kshkid · 04-02-2007, 12:23 PM

to be more specific

i go for

Code:

if( fd == (FILE*) NULL ) {
  exit(1);
}

haxpor · 04-02-2007, 01:10 PM

You should print out outbuff to test the result.

Anyway the fread() function will return the number of objects read, in this case your each object is 1 byte long (because char is used).

The result you see that it print 0 for read_bytes, it is correct because it read successfully in 1 time so you dont have to put it in while loop (but i suggest everytime dealing with read/write IO function you should put it in while loop to check if the byte or object it read is still more than 0) .

That is, you have read to the end of file already. Just check outbuff, if I correct then.