Reads data from a file.
Description |
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The read() function attempts to read nbyte bytes from the
open file associated with the open file descriptor fildes into the buffer pointed to by buffer.
On a file capable of seeking, read() starts from the current file offset position. Before successful return, the file offset is incremented by the number of bytes actually read.
On a file not capable of seeking, read() starts from the current position. (The file offset for such a file is undefined.)
Upon successful completion, the read() function returns the actual number of bytes copied to the buffer and, if nbyte is greater than 0, marks for update the st_atime time field of the file.
The value returned by read() is never greater than nbyte. The value returned may be less than nbyte if either the number of bytes left in the file is less than nbyte or the file is a special file (STDIN_FILENO) and fewer than nbytes are available.
If nbytes is zero, the read() function returns zero bytes of data. In this case, the file offset position is not changed, and no time fields are marked for update.
No data transfer occurs past the current end-of-file (EOF). Zero is returned if the file offset position is at or after the EOF. For any portion of the file prior to the EOF that is not written to, read() returns bytes with a value of zero.
Implementation Considerations |
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Refer to the EFAULT, EIMPL, and ESYSERR error descriptions below.
Signals generated for the calling process during execution of read() are deferred from delivery until completion of this function.
See Also |
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creat(), dup(), execl(), execv(), fork(), open(), unlink(), POSIX.1 (Section 6.4.1)
