Difference between opening a file in binary vs text

Question

I ve done some stuff like   FILE  a   fopen  a txt    w    const char  data    abc123   fwrite data  6  1  a   fclose a     and then in the generated text file  it says  abc123  just like expected  But then I do     this time it is  wb  not just  w  FILE  a   fopen  a txt    wb    const char  data    abc123   fwrite data  6  1  a   fclose a     and get the exact same result  If I read the file using binary or normal mode  it also gives me the same result  So my question is  what is the difference between fopening with or without binary mode   Where I read about fopen modes  http   www cplusplus com reference cstdio fopen

User · Accepted Answer

The link you gave does actually describe the differences, but it's buried at the bottom of the page:

http://www.cplusplus.com/reference/cstdio/fopen/

Text files are files containing sequences of lines of text. Depending on the environment where the application runs, some special character conversion may occur in input/output operations in text mode to adapt them to a system-specific text file format. Although on some environments no conversions occur and both text files and binary files are treated the same way, using the appropriate mode improves portability.

The conversion could be to normalize \r\n to \n (or vice-versa), or maybe ignoring characters beyond 0x7F (a-la 'text mode' in FTP). Personally I'd open everything in binary-mode and use a good text-encoding library for dealing with text.

User · Answer

The most important difference to be aware of is that with a stream opened in text mode you get newline translation on non- nix systems  it s also used for network communications  but this isn t supported by the standard library   In  nix newline is just ASCII linefeed   n  both for internal and external representation of text  In Windows the external representation often uses a carriage return   linefeed pair   CRLF   ASCII codes 13 and 10   which is converted to a single  n on input  and conversely on output     From the C99 standard  the N869 draft document     7 19 2 2      A text stream is an ordered sequence of characters composed into lines  each line   consisting of zero or more characters plus a terminating new-line character  Whether the   last line requires a terminating new-line character is implementation-defined  Characters   may have to be added  altered  or deleted on input and output to conform to differing   conventions for representing text in the host environment  Thus  there need not be a one-   to-one correspondence between the characters in a stream and those in the external   representation  Data read in from a text stream will necessarily compare equal to the data   that were earlier written out to that stream only if  the data consist only of printing   characters and the control characters horizontal tab and new-line  no new-line character is   immediately preceded by space characters  and the last character is a new-line character    Whether space characters that are written out immediately before a new-line character   appear when read in is implementation-defined    And in   7 19 3 2     Binary files are not truncated  except as defined in 7 19 5 3  Whether a write on a text   stream causes the associated file to be truncated beyond that point is implementation-   defined    About use of fseek  in   7 19 9 2 4      For a text stream  either offset shall be zero  or offset shall be a value returned by   an earlier successful call to the ftell function on a stream associated with the same file and whence shall be SEEK SET    About use of ftell  in   17 19 9 4      The ftell function obtains the current value of the file position indicator for the stream pointed to by stream  For a binary stream  the value is the number of characters from the beginning of the file  For a text stream  its file position indicator contains unspecified information  usable by the fseek function for returning the file position indicator for the stream to its position at the time of the ftell call  the difference between two such return values is not necessarily a meaningful measure of the number of characters written or read    I think that rsquo s the most important  but there are some more details

[c++] Difference between opening a file in binary vs text

Examples related to c++

Examples related to file

Examples related to text

Examples related to binary