Sponsored Content
Full Discussion: Understanding lseek
Top Forums UNIX for Dummies Questions & Answers Understanding lseek Post 302705301 by jim mcnamara on Monday 24th of September 2012 01:49:10 PM
Old 09-24-2012
File pointers do not necesarily have any relevance to file size. Use fstat() on an open file. lseek() is meant to move file pointers, other uses may not work as you found out.

Code:
#include <sys/stat.h>
size_t filesize(int fd)
{
    struct stat st;
    if(fstat(fd, &st)==-1)
    {
        perror("Cannot stat file");
        exit(1);
    }
    return st.st_size;
}

// usage someplace else in your code

FILE *in=fopen(somefile.dat, "a");
size_t sz=filesize(fileno(in));

 

9 More Discussions You Might Find Interesting

1. Programming

lseek in c

sir, i used lssek as this lseek(fp,-10,2); i am not getting any output i dont now why can you explan sir.. Thanks in advance, Arunkumar (4 Replies)
Discussion started by: arunkumar_mca
4 Replies

2. Shell Programming and Scripting

need help understanding mv

I just started shell coding and I'm a bit confused on how 'mv' works can someone explain to me how it works and if i did this correctly. Thanks. echo "Enter Name of the first file:" read file1 #echo $file1 if ; then echo "Sorry, file does not exist." exit 1 ... (16 Replies)
Discussion started by: taiL
16 Replies

3. Programming

Hairy Problem! lseek over 4G

recently my project needs me to lseek a position over 4G size.... i found in linux or unix the parameters are all ulong 32 bits...the limit dooms the movement of a position over 4G I was told that i should lseek64 to meet my need... but i have no idea where i can get the function neither by "man... (8 Replies)
Discussion started by: macroideal
8 Replies

4. UNIX for Dummies Questions & Answers

understanding {%/*}/

Hi Gurus: I am trying to understand the following line of code.I did enough of googling to understand but no luck.Please help me understand the follow chunk of code: X=$0 MOD=${X%/*}/env.ksh X is the current script from which I am trying to execute. Say if X=test.ksh $MOD is echoing :... (3 Replies)
Discussion started by: vemana
3 Replies

5. UNIX for Dummies Questions & Answers

lseek() equivalent

I know there is lseek() function that will allow to write or read from certain position in the file. Is there similar function that will let do same but for array rather then file? (9 Replies)
Discussion started by: joker40
9 Replies

6. UNIX for Dummies Questions & Answers

Lseek implementation

Hi everybody, i've been googling for ages now and gotten kinda desperate... The question, however, might be rather trivial for the experts: What is it exactly, i.e. physically, the POSIX function (for a file) "lseek" does? Does it trigger some kind of synchronization on disk? Is it just for the... (4 Replies)
Discussion started by: Humudituu
4 Replies

7. Programming

what is the main difference between difference between using nonatomic lseek and O_APPEND

I think both write at the end of the file ...... but is there a sharp difference between those 2 instruction ..... thank you this is my 3rd question today forgive me :D (1 Reply)
Discussion started by: fwrlfo
1 Replies

8. AIX

Backup: The lseek call failed

Hi, We are facing issues while backing up our 1205 GB filesystem on LTO5 Tape. During backup the "backup: The lseek call failed." messages were generated, I want to know why these messages were generating AIX version is: 6100-08-00-0000 backup: The date of this level 0 backup is Mon Mar 11... (4 Replies)
Discussion started by: m_raheelahmed
4 Replies

9. Programming

Problem with lseek call.

The following code: int fd; if (fd = open("mem", O_RDONLY) == -1) return 1; if (lseek(fd, 0, SEEK_SET) == -1) { char *buf = malloc(512); buf = strerror(errno); printf("%s\n", buf); return 1; } always returns with "illegal seek"... (2 Replies)
Discussion started by: Sir_Tomasz
2 Replies
FILESIZE(3)								 1							       FILESIZE(3)

filesize - Gets file size

SYNOPSIS
int filesize (string $filename) DESCRIPTION
Gets the size for the given file. PARAMETERS
o $filename - Path to the file. RETURN VALUES
Returns the size of the file in bytes, or FALSE (and generates an error of level E_WARNING) in case of an error. Note Because PHP's integer type is signed and many platforms use 32bit integers, some filesystem functions may return unexpected results for files which are larger than 2GB. EXAMPLES
Example #1 filesize(3) example <?php // outputs e.g. somefile.txt: 1024 bytes $filename = 'somefile.txt'; echo $filename . ': ' . filesize($filename) . ' bytes'; ?> ERRORS
/EXCEPTIONS Upon failure, an E_WARNING is emitted. NOTES
Note The results of this function are cached. See clearstatcache(3) for more details. Tip As of PHP 5.0.0, this function can also be used with some URL wrappers. Refer to "Supported Protocols and Wrappers" to determine which wrappers support stat(3) family of functionality. SEE ALSO
file_exists(3). PHP Documentation Group FILESIZE(3)
All times are GMT -4. The time now is 12:59 PM.
Unix & Linux Forums Content Copyright 1993-2022. All Rights Reserved.
Privacy Policy