How can I get a file s size in C

Question

Let s create a complementary question to this one  What is the most common way to get the file size in C    Before answering  make sure it is portable  may be executed on Unix  Mac and Windows   reliable  easy to understand and without library dependencies  no boost or qt  but for instance glib is ok since it is portable library

User · Answer

You need to seek to the end of the file and then ask for the position:

fseek(fp, 0L, SEEK_END);
sz = ftell(fp);

You can then seek back, e.g.:

fseek(fp, 0L, SEEK_SET);

or (if seeking to go to the beginning)

rewind(fp);

User · Answer

Have you considered not computing the file size and just growing the array if necessary   Here s an example  with error checking ommitted     define CHUNK 1024     Read the contents of a file into a buffer   Return the size of the file     and set buf to point to a buffer allocated with malloc that contains      the file contents      int read file FILE  fp  char   buf       int n  np    char  b   b2     n   CHUNK    np   n    b   malloc sizeof char  n     while   r   fread b  sizeof char   CHUNK  fp    gt  0        n    r      if  np - n  lt  CHUNK           np    2                          buffer is too small  the next read could overflow        b2   malloc np sizeof char          memcpy b2  b  n   sizeof char          free b         b   b2               buf   b    return n      This has the advantage of working even for streams in which it is impossible to get the file size  like stdin

User · Answer

How to use lseek fseek stat fstat to get filesize     include  lt fcntl h gt   include  lt unistd h gt   include  lt stdio h gt   include  lt stdlib h gt   include  lt sys stat h gt    void fseek filesize const char  filename        FILE  fp   NULL      long off       fp   fopen filename   r        if  fp    NULL                printf  failed to fopen  s n   filename           exit EXIT FAILURE              if  fseek fp  0  SEEK END     -1                printf  failed to fseek  s n   filename           exit EXIT FAILURE              off   ftell fp       if  off     long -1                printf  failed to ftell  s n   filename           exit EXIT FAILURE              printf      fseek filesize - file   s  size   ld n   filename  off        if  fclose fp     0                printf  failed to fclose  s n   filename           exit EXIT FAILURE            void fstat filesize const char  filename        int fd      struct stat statbuf       fd   open filename  O RDONLY  S IRUSR   S IRGRP       if  fd    -1                printf  failed to open  s n   filename           exit EXIT FAILURE              if  fstat fd   amp statbuf     -1                printf  failed to fstat  s n   filename           exit EXIT FAILURE              printf      fstat filesize - file   s  size   lld n   filename  statbuf st size        if  close fd     -1                printf  failed to fclose  s n   filename           exit EXIT FAILURE            void stat filesize const char  filename        struct stat statbuf       if  stat filename   amp statbuf     -1                printf  failed to stat  s n   filename           exit EXIT FAILURE              printf      stat filesize - file   s  size   lld n   filename  statbuf st size       void seek filesize const char  filename        int fd      off t off       if  filename    NULL                printf  invalid filename n            exit EXIT FAILURE              fd   open filename  O RDONLY  S IRUSR   S IRGRP       if  fd    -1                printf  failed to open  s n   filename           exit EXIT FAILURE              off   lseek fd  0  SEEK END       if  off     off t -1                printf  failed to lseek  s n   filename           exit EXIT FAILURE              printf      seek filesize - file   s  size   lld n   filename  off        if  close fd     -1                printf  failed to close  s n   filename           exit EXIT FAILURE            int main int argc  const char  argv          int i       if  argc  lt  2                printf   s  lt file1 gt   lt file2 gt     n   argv 0            exit 0              for i   1  i  lt  argc  i                  seek filesize argv i            stat filesize argv i            fstat filesize argv i            fseek filesize argv i               return 0

User · Answer

include  lt stdio h gt    define MAXNUMBER 1024  int main         int i      char a MAXNUMBER        FILE  fp   popen  du -b   bin bash    r         while  a i      getc fp     9                 a i     0        printf   a is  s n   a        pclose fp       return 0        HTH

User · Answer

Using the C   filesystem library   include  lt filesystem gt   int main int argc  char  argv        std  filesystem  path p argv 1       std  cout  lt  lt   quot The size of  quot   lt  lt  p u8string    lt  lt   quot  is  quot   lt  lt        std  filesystem  file size p   lt  lt   quot  bytes  n quot

User · Answer

If you re on Linux  seriously consider just using the g file get contents function from glib   It handles all the code for loading a file  allocating memory  and handling errors

User · Answer

include  lt stdio h gt    define MAXNUMBER 1024  int main         int i      char a MAXNUMBER        FILE  fp   popen  du -b   bin bash    r         while  a i      getc fp     9                 a i     0        printf   a is  s n   a        pclose fp       return 0        HTH

User · Answer

I ended up just making a short and sweet fsize function note  no error checking   int fsize FILE  fp       int prev ftell fp       fseek fp  0L  SEEK END       int sz ftell fp       fseek fp prev SEEK SET     go back to where we were     return sz      It s kind of silly that the standard C library doesn t have such a function  but I can see why it d be difficult as not every  file  has a size for instance  dev null

User · Answer

You need to seek to the end of the file and then ask for the position:

fseek(fp, 0L, SEEK_END);
sz = ftell(fp);

You can then seek back, e.g.:

fseek(fp, 0L, SEEK_SET);

or (if seeking to go to the beginning)

rewind(fp);

User · Answer

Using standard library   Assuming that your implementation meaningfully supports SEEK END   fseek f  0  SEEK END      seek to end of file size   ftell f      get current file pointer fseek f  0  SEEK SET      seek back to beginning of file    proceed with allocating memory and reading the file   Linux POSIX   You can use stat  if you know the filename   or fstat  if you have the file descriptor    Here is an example for stat    include  lt sys stat h gt  struct stat st  stat filename   amp st   size   st st size    Win32   You can use GetFileSize or GetFileSizeEx

User · Answer

If you have the file descriptor fstat   returns a stat structure which contain the file size    include  lt sys types h gt   include  lt sys stat h gt   include  lt unistd h gt      fd   fileno f     if you have a stream  e g  from fopen   not a file descriptor  struct stat buf  fstat fd   amp buf   off t size   buf st size

User · Answer

You need to seek to the end of the file and then ask for the position:

fseek(fp, 0L, SEEK_END);
sz = ftell(fp);

You can then seek back, e.g.:

fseek(fp, 0L, SEEK_SET);

or (if seeking to go to the beginning)

rewind(fp);

User · Answer

Using standard library   Assuming that your implementation meaningfully supports SEEK END   fseek f  0  SEEK END      seek to end of file size   ftell f      get current file pointer fseek f  0  SEEK SET      seek back to beginning of file    proceed with allocating memory and reading the file   Linux POSIX   You can use stat  if you know the filename   or fstat  if you have the file descriptor    Here is an example for stat    include  lt sys stat h gt  struct stat st  stat filename   amp st   size   st st size    Win32   You can use GetFileSize or GetFileSizeEx

User · Answer

If you re on Linux  seriously consider just using the g file get contents function from glib   It handles all the code for loading a file  allocating memory  and handling errors

User · Answer

You need to seek to the end of the file and then ask for the position:

fseek(fp, 0L, SEEK_END);
sz = ftell(fp);

You can then seek back, e.g.:

fseek(fp, 0L, SEEK_SET);

or (if seeking to go to the beginning)

rewind(fp);

User · Answer

Have you considered not computing the file size and just growing the array if necessary   Here s an example  with error checking ommitted     define CHUNK 1024     Read the contents of a file into a buffer   Return the size of the file     and set buf to point to a buffer allocated with malloc that contains      the file contents      int read file FILE  fp  char   buf       int n  np    char  b   b2     n   CHUNK    np   n    b   malloc sizeof char  n     while   r   fread b  sizeof char   CHUNK  fp    gt  0        n    r      if  np - n  lt  CHUNK           np    2                          buffer is too small  the next read could overflow        b2   malloc np sizeof char          memcpy b2  b  n   sizeof char          free b         b   b2               buf   b    return n      This has the advantage of working even for streams in which it is impossible to get the file size  like stdin

User · Answer

include  lt stdio h gt    define MAXNUMBER 1024  int main         int i      char a MAXNUMBER        FILE  fp   popen  du -b   bin bash    r         while  a i      getc fp     9                 a i     0        printf   a is  s n   a        pclose fp       return 0        HTH

User · Answer

In c   you can use following function  it will return the size of you file in bytes    include  lt fstream gt   int fileSize const char  add       ifstream mySource      mySource open add  ios base  binary       mySource seekg 0 ios base  end       int size   mySource tellg        mySource close        return size

User · Answer

If you have the file descriptor fstat   returns a stat structure which contain the file size    include  lt sys types h gt   include  lt sys stat h gt   include  lt unistd h gt      fd   fileno f     if you have a stream  e g  from fopen   not a file descriptor  struct stat buf  fstat fd   amp buf   off t size   buf st size

User · Answer

include  lt fstream gt   std  ifstream  pos type filesize const char  filename        std  ifstream in filename  std  ifstream  ate   std  ifstream  binary       return in tellg         See http   www cplusplus com doc tutorial files  for more information on files in C     edit  this answer is not correct since tellg   does not necessarily return the right value  See http   stackoverflow com a 22986486 1835769

User · Answer

If you have the file descriptor fstat   returns a stat structure which contain the file size    include  lt sys types h gt   include  lt sys stat h gt   include  lt unistd h gt      fd   fileno f     if you have a stream  e g  from fopen   not a file descriptor  struct stat buf  fstat fd   amp buf   off t size   buf st size

User · Answer

While not necessarily the most popular method  I ve heard that the ftell  fseek method may not always give accurate results in some circumstances   Specifically  if an already opened file is used and the size needs to be worked out on that and it happens to be opened as a text file  then it s going to give out wrong answers   The following methods should always work as stat is part of the c runtime library on Windows  Mac and Linux   long GetFileSize std  string filename        struct stat stat buf      int rc   stat filename c str     amp stat buf       return rc    0   stat buf st size   -1     or   long FdGetFileSize int fd        struct stat stat buf      int rc   fstat fd   amp stat buf       return rc    0   stat buf st size   -1      On some systems there is also a stat64 fstat64   So if you need this for very large files you may want to look at using those

User · Answer

If you re on Linux  seriously consider just using the g file get contents function from glib   It handles all the code for loading a file  allocating memory  and handling errors

User · Answer

Using standard library   Assuming that your implementation meaningfully supports SEEK END   fseek f  0  SEEK END      seek to end of file size   ftell f      get current file pointer fseek f  0  SEEK SET      seek back to beginning of file    proceed with allocating memory and reading the file   Linux POSIX   You can use stat  if you know the filename   or fstat  if you have the file descriptor    Here is an example for stat    include  lt sys stat h gt  struct stat st  stat filename   amp st   size   st st size    Win32   You can use GetFileSize or GetFileSizeEx

User · Answer

include  lt stdio h gt  int main         FILE  f      f   fopen  mainfinal c     r        fseek f  0  SEEK END       unsigned long len    unsigned long ftell f       printf   ld n   len       fclose f

User · Answer

include  lt stdio h gt    define MAXNUMBER 1024  int main         int i      char a MAXNUMBER        FILE  fp   popen  du -b   bin bash    r         while  a i      getc fp     9                 a i     0        printf   a is  s n   a        pclose fp       return 0        HTH

User · Answer

If you have the file descriptor fstat   returns a stat structure which contain the file size    include  lt sys types h gt   include  lt sys stat h gt   include  lt unistd h gt      fd   fileno f     if you have a stream  e g  from fopen   not a file descriptor  struct stat buf  fstat fd   amp buf   off t size   buf st size

User · Answer

Using standard library   Assuming that your implementation meaningfully supports SEEK END   fseek f  0  SEEK END      seek to end of file size   ftell f      get current file pointer fseek f  0  SEEK SET      seek back to beginning of file    proceed with allocating memory and reading the file   Linux POSIX   You can use stat  if you know the filename   or fstat  if you have the file descriptor    Here is an example for stat    include  lt sys stat h gt  struct stat st  stat filename   amp st   size   st st size    Win32   You can use GetFileSize or GetFileSizeEx

User · Answer

It is also possible to find that out using the fopen   fseek   and ftell   function   int get file size std  string filename     path to file       FILE  p file   NULL      p file   fopen filename c str    rb        fseek p file 0 SEEK END       int size   ftell p file       fclose p file       return size

User · Answer

The code snippet below exactly addresses the question in this   post              Get me my file size in bytes  long long to support any file size supported by your OS      long long Logger  getFileSize         std  streampos fsize   0       std  ifstream myfile   myfile txt   ios  in       File is of type const char       fsize   myfile tellg               The file pointer is currently at the beginning     myfile seekg 0  ios  end           Place the file pointer at the end of file      fsize   myfile tellg   - fsize      myfile close         static assert sizeof fsize   gt   sizeof long long    Oops          cout  lt  lt   size is     lt  lt  fsize  lt  lt    bytes  n       return fsize

User · Answer

How to use lseek fseek stat fstat to get filesize     include  lt fcntl h gt   include  lt unistd h gt   include  lt stdio h gt   include  lt stdlib h gt   include  lt sys stat h gt    void fseek filesize const char  filename        FILE  fp   NULL      long off       fp   fopen filename   r        if  fp    NULL                printf  failed to fopen  s n   filename           exit EXIT FAILURE              if  fseek fp  0  SEEK END     -1                printf  failed to fseek  s n   filename           exit EXIT FAILURE              off   ftell fp       if  off     long -1                printf  failed to ftell  s n   filename           exit EXIT FAILURE              printf      fseek filesize - file   s  size   ld n   filename  off        if  fclose fp     0                printf  failed to fclose  s n   filename           exit EXIT FAILURE            void fstat filesize const char  filename        int fd      struct stat statbuf       fd   open filename  O RDONLY  S IRUSR   S IRGRP       if  fd    -1                printf  failed to open  s n   filename           exit EXIT FAILURE              if  fstat fd   amp statbuf     -1                printf  failed to fstat  s n   filename           exit EXIT FAILURE              printf      fstat filesize - file   s  size   lld n   filename  statbuf st size        if  close fd     -1                printf  failed to fclose  s n   filename           exit EXIT FAILURE            void stat filesize const char  filename        struct stat statbuf       if  stat filename   amp statbuf     -1                printf  failed to stat  s n   filename           exit EXIT FAILURE              printf      stat filesize - file   s  size   lld n   filename  statbuf st size       void seek filesize const char  filename        int fd      off t off       if  filename    NULL                printf  invalid filename n            exit EXIT FAILURE              fd   open filename  O RDONLY  S IRUSR   S IRGRP       if  fd    -1                printf  failed to open  s n   filename           exit EXIT FAILURE              off   lseek fd  0  SEEK END       if  off     off t -1                printf  failed to lseek  s n   filename           exit EXIT FAILURE              printf      seek filesize - file   s  size   lld n   filename  off        if  close fd     -1                printf  failed to close  s n   filename           exit EXIT FAILURE            int main int argc  const char  argv          int i       if  argc  lt  2                printf   s  lt file1 gt   lt file2 gt     n   argv 0            exit 0              for i   1  i  lt  argc  i                  seek filesize argv i            stat filesize argv i            fstat filesize argv i            fseek filesize argv i               return 0

User · Answer

I ended up just making a short and sweet fsize function note  no error checking   int fsize FILE  fp       int prev ftell fp       fseek fp  0L  SEEK END       int sz ftell fp       fseek fp prev SEEK SET     go back to where we were     return sz      It s kind of silly that the standard C library doesn t have such a function  but I can see why it d be difficult as not every  file  has a size for instance  dev null

User · Answer

If you re on Linux  seriously consider just using the g file get contents function from glib   It handles all the code for loading a file  allocating memory  and handling errors

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