How to get the size of a file

Question

Possible Duplicate:
Using C++ filestreams (fstream), how can you determine the size of a file?
file size in c program

I want to retrive the size of a file and for this I implemented in this way

(void)fseek(m_fp, 0, SEEK_END); // Set the file pointer to the end of the file
pFileSize = ftell(m_fp);        // Get the file size
(void)fseek(m_fp, oldFilePos, SEEK_SET);  // Put back the file pointer at the original location

This is not feasible for out need and is ther anyother way to get the file size or check whether the file contain and data

possible duplicate: http://stackoverflow.com/q/2409504/1025391 — moooeeeep, Oct 09 '12 at 07:18
@moooeeeep Because it invokes undefined behavior? From the C standard: `A binary stream need not meaningfully support fseek calls with a whence value of SEEK_END.`, `Setting the file position indicator to end-of-file, as with fseek(file, 0, SEEK_END), has undefined behavior for a binary stream...` — Alexey Frunze, Oct 09 '12 at 09:08
@AlexeyFrunze that is indeed nice to know. But the OP didn't specify that he's dealing with a binary stream. — moooeeeep, Oct 09 '12 at 09:16
@moooeeeep: For a text file, it's not the size of the file either. — MSalters, Oct 09 '12 at 14:16
If you're not afraid of the cutting edge, [`std::tr2::file_size`](http://msdn.microsoft.com/en-us/library/hh874829) — MSalters, Oct 09 '12 at 14:18
This is a duplicate, but not of 2409504. This question is more about C than C++, so 5757353 is a more accurate duplicate. — William Pursell, Oct 10 '12 at 00:47

score 6 · Answer 1 · answered Oct 09 '12 at 07:03

6

You can use stat

#include <sys/types.h>
#include <sys/stat.h>
#if defined (_WIN32)
#  include <io.h> // make portable for windows
#else
#include <unistd.h>
#endif

struct stat st;
stat (filename, &st);
std::cout << st.st_size;

answered Oct 09 '12 at 07:03

tozka

2,751
16
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Note that stat is not a part of C or C++ but POSIX. – P.P Oct 09 '12 at 07:07
fstat() or fstat64() are variations on stat() that use a FILE *. Given you already have m_fp in your code, I suggest you use fstat(). – Concrete Gannet Oct 09 '12 at 07:12
[fstat ()](http://linux.die.net/man/2/fstat) uses int file handle (returned by `open`) and not `FILE*` (from `fopen`) – tozka Oct 09 '12 at 07:18

score 0 · Answer 2 · answered Oct 09 '12 at 07:04

0

If it is a binary stream, then pFileSize is the number of bytes from oldFilePos to the end of the file.

answered Oct 09 '12 at 07:04

kuniqs

198
9

From the C standard: `A binary stream need not meaningfully support fseek calls with a whence value of SEEK_END.`, `Setting the file position indicator to end-of-file, as with fseek(file, 0, SEEK_END), has undefined behavior for a binary stream...` – Alexey Frunze Oct 09 '12 at 09:07

score 0 · Answer 3 · answered Oct 09 '12 at 07:59

0

What you wrote is a 100% multiplatform way of doing what you need. Use your operating system's calls to do more, stat() on Unix-like OSes or GetFileAttributesEx() on Windows.

answered Oct 09 '12 at 07:59

LubosD

710
5
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-1. No, it's not. From the C standard: `A binary stream need not meaningfully support fseek calls with a whence value of SEEK_END.`, `Setting the file position indicator to end-of-file, as with fseek(file, 0, SEEK_END), has undefined behavior for a binary stream...` – Alexey Frunze Oct 09 '12 at 09:06
Is there actually such a platform that doesn't support SEEK_END in stdio? – LubosD Oct 12 '12 at 11:50
I can't tell your for sure what platforms (compilers/stdlibs/OSes) don't support it, but I think I have been beaten by it once. – Alexey Frunze Oct 12 '12 at 11:54

How to get the size of a file

3 Answers3