How do you determine the size of a file in C

Question

How can I figure out the size of a file  in bytes    include  lt stdio h gt   unsigned int fsize char  file       what goes here

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Don t do this  why         Quoting the C99 standard doc that i found online    Setting the file position indicator to end-of-file  as with fseek file  0  SEEK END   has undefined behavior for a binary stream  because of possible trailing null characters  or for any stream with state-dependent encoding that does not assuredly end in the initial shift state      Change the definition to int so that error messages can be transmitted  and then use fseek   and ftell   to determine the file size   int fsize char  file      int size    FILE  fh     fh   fopen file   rb      binary mode   if fh    NULL       if  fseek fh  0  SEEK END           fclose fh         return -1             size   ftell fh       fclose fh       return size         return -1    error

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If you re fine with using the std c library    include  lt sys stat h gt  off t fsize char  file        struct stat filestat      if  stat file   amp filestat     0            return filestat st size            return 0

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And if you re building a Windows app  use the GetFileSizeEx API as CRT file I O is messy  especially for determining file length  due to peculiarities in file representations on different systems

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POSIX  The POSIX standard has its own method to get file size   Include the sys stat h header to use the function   Synopsis   Get file statistics using stat 3   Obtain the st size property    Examples  Note  It limits the size to 4GB  If not Fat32 filesystem then use the  64bit version     include  lt stdio h gt   include  lt sys stat h gt   int main int argc  char   argv        struct stat info      stat argv 1    amp info            st  is an acronym of  stat      printf   s  size  ld n   argv 1   info st size        include  lt stdio h gt   include  lt sys stat h gt   int main int argc  char   argv        struct stat64 info      stat64 argv 1    amp info            st  is an acronym of  stat      printf   s  size  ld n   argv 1   info st size       ANSI C  standard   The ANSI C doesn t directly provides the way to determine the length of the file   We ll have to use our mind  For now  we ll use the seek approach   Synopsis   Seek the file to the end using fseek 3   Get the current position using ftell 3     Example   include  lt stdio h gt   int main int argc  char   argv        FILE  fp   fopen argv 1        int f size       fseek fp  0  SEEK END       f size   ftell fp       rewind fp      to back to start again      printf   s  size  ld    unsigned long f size          If the file is stdin or a pipe  POSIX  ANSI C won t work       It will going return 0 if the file is a pipe or stdin       Opinion    You should use POSIX standard instead  Because  it has 64bit support

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You can open the file  go to 0 offset relative from the bottom of the file with    define SEEKBOTTOM   2  fseek handle  0  SEEKBOTTOM      the value returned from fseek is the size of the file   I didn t code in C for a long time  but I think it should work

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Based on NilObject s code    include  lt sys stat h gt   include  lt sys types h gt   off t fsize const char  filename        struct stat st        if  stat filename   amp st     0          return st st size       return -1       Changes    Made the filename argument a const char  Corrected the struct stat definition  which was missing the variable name  Returns -1 on error instead of 0  which would be ambiguous for an empty file  off t is a signed type so this is possible    If you want fsize   to print a message on error  you can use this    include  lt sys stat h gt   include  lt sys types h gt   include  lt string h gt   include  lt stdio h gt   include  lt errno h gt   off t fsize const char  filename        struct stat st       if  stat filename   amp st     0          return st st size       fprintf stderr   Cannot determine size of  s   s n               filename  strerror errno         return -1      On 32-bit systems you should compile this with the option -D FILE OFFSET BITS 64  otherwise off t will only hold values up to 2 GB  See the  Using LFS  section of Large File Support in Linux for details

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Looking at the question  ftell can easily get the number of bytes      long size   ftell FILENAME     printf  total size is  ld bytes  size

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I found a method using fseek and ftell and a thread with this question with answers that it can t be done in just C in another way  You could use a portability library like NSPR  the library that powers Firefox

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I have a function that works well with only stdio h  I like it a lot and it works very well and is pretty concise   size t fsize FILE  File        size t FSZ      fseek File  0  2       FSZ   ftell File       rewind File       return FSZ

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I used this set of code to find the file length     opens a file with a file descriptor FILE   i file  i file   fopen source   r       gets a long from the file descriptor for fstat long f d   fileno i file   struct stat buffer  fstat f d   amp buffer      stores file size long file length   buffer st size  fclose i file

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Try this --  fseek fp  0  SEEK END   unsigned long int file size   ftell fp   rewind fp     What this does is first  seek to the end of the file  then  report where the file pointer is  Lastly  this is optional  it rewinds back to the beginning of the file  Note that fp should be a binary stream    file size contains the number of bytes the file contains  Note that since  according to climits h  the unsigned long type is limited to 4294967295 bytes  4 gigabytes  you ll need to find a different variable type if you re likely to deal with files larger than that

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Matt s solution should work  except that it s C   instead of C  and the initial tell shouldn t be necessary   unsigned long fsize char  file        FILE   f   fopen file   r        fseek f  0  SEEK END       unsigned long len    unsigned long ftell f       fclose f       return len      Fixed your brace for you  too       Update  This isn t really the best solution   It s limited to 4GB files on Windows and it s likely slower than just using a platform-specific call like GetFileSizeEx or stat64

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Here s a simple and clean function that returns the file size   long get file size char  path        FILE  fp      long size   -1         Open file for reading        fp   fopen path   r        fseek fp  0  SEEK END       size   ftell fp        fp close        return

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Don t use int  Files over 2 gigabytes in size are common as dirt these days  Don t use unsigned int  Files over 4 gigabytes in size are common as some slightly-less-common dirt  IIRC the standard library defines off t as an unsigned 64 bit integer  which is what everyone should be using  We can redefine that to be 128 bits in a few years when we start having 16 exabyte files hanging around   If you re on windows  you should use GetFileSizeEx - it actually uses a signed 64 bit integer  so they ll start hitting problems with 8 exabyte files  Foolish Microsoft   -

[c] How do you determine the size of a file in C?

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