fopen二进制方式和文本方式打开的区别

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fopen是一个库函数。

不是系统调用，系统调用是没有什么b或者有b一说的。

库函数严格意义上来说，就要分平台实现了，虽然现在有各种各样的标准，比如POSIX， ANSIC等等，但是还是要有这种库函数分平台的意识。

就fopen这个函数就在不同的平台就有不同的实现

win平台：

我基本没有怎么用过，搜了下网上这篇文章：

https://blog.csdn.net/u012372584/article/details/77836168

整体上就是对于回车换行在读写的时候会有不同的操作，其它的不得而知。

linux平台：

有没有b都是一样的，没有文本方式二进制方式一说。

 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.)

这个是fopen在linux上面官方文档的说明。

POSIX：

对fopen使用b的介绍为：

The character 'b' shall have no effect, but is allowed for ISO C
       standard conformance.  Opening a file with read mode (r as the first
       character in the mode argument) shall fail if the file does not exist
       or cannot be read.

也是没有什么用，但是可以带。