c++ - 为什么pread不能保证读取所有指定的字节？

Question

我用 C++ 编程，发现 pread 的工作非常有趣。

pread() 返回读取的字节数。返回的读取字节数可能与指定的要读取的字节数不同。

为什么pread不能保证读取所有指定的字节？

这个限制从何而来？

Answer 1

this may happen for example because fewer bytes are actually available right now (maybe because we were close to end-of-file, or because we are reading from a pipe, or from a terminal), or because read() was interrupted by a signal. On error, -1 is returned, and errno is set appropriately. In this case it is left unspecified whether the file position (if any) changes.

来自 https://linux.die.net/man/2/read