what s the differences between r and rb in fopen

Question

I tried using fopen in C  the second parameter is the open mode  The two modes  r  and  rb  tend to confuse me a lot  It seems they are the same  But sometimes it is better to use  rb   So  why does  r  exist  Explain it to me in detail or with examples  Thank You

User · Answer

r  is the same as  rt  for Translated mode  rb  is non-translated mode    This makes a difference on Windows  at least  See that link for details

User · Answer

use  rb  to open a binary file  Then the bytes of the file won t be encoded when you read them

User · Answer

On most POSIX systems  it is ignored  But  check your system to be sure   XNU     The mode string can also include the letter  b  either as last character or as a character between the characters in any of the two-character strings described above   This is strictly for compatibility with ISO IEC 9899 1990   ISO C90   and has no effect  the  b  is ignored    Linux     The mode string can also include the letter  b  either as a last   character or as a character between the characters in any of the two-   character strings described above   This is strictly for   compatibility with C89 and has no effect  the  b  is ignored on all   POSIX conforming systems  including Linux    Other systems may treat   text files and binary files differently  and adding the  b  may be a   good idea if you do I O to a binary file and expect that your program   may be ported to non-UNIX environments

User · Answer

You should use  r  for opening text files   Different operating systems have slightly different ways of storing text  and this will perform the correct translations so that you don t need to know about the idiosyncracies of the local operating system   For example  you will know that newlines will always appear as a simple   n   regardless of where the code runs   You should use  rb  if you re opening non-text files  because in this case  the translations are not appropriate

User · Answer

On Linux  and Unix in general   r  and  rb  are the same   More specifically  a FILE pointer obtained by fopen  ing a file in  in text mode and in binary mode behaves the same way on Unixes   On windows  and in general  on systems that use more than one character to represent  newlines   a file opened in text mode behaves as if all those characters are just one character    n    If you want to portably read write text files on any system  use  r   and  w  in fopen     That will guarantee that the files are written and read properly   If you are opening a binary file  use  rb  and  wb   so that an unfortunate newline-translation doesn t mess your data   Note that a consequence of the underlying system doing the newline translation for you is that you can t determine the number of bytes you can read from a file using fseek file  0  SEEK END    Finally  see What s the difference between text and binary I O  on comp lang c FAQs

[c] what's the differences between r and rb in fopen

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