read (system call)
 | This article includes a improve this article by introducing more precise citations. (February 2019) ) |
In modern
operating systems, a program that needs to access data from a file stored in a file system uses the read system call. The file is identified by a file descriptor that is normally obtained from a previous call to open. This system call reads in data in bytes
, the number of which is specified by the caller, from the file and stores then into a buffer supplied by the calling process.
The read system call takes three arguments:
- The file descriptor of the file.
- the buffer where the read data is to be stored and
- the number of bytes to be read from the file.
POSIX usage
The read system call interface is standardized by the POSIX specification. Data from a file is read by calling the read function:
ssize_t read(int fd, void *buf, size_t count);
The value returned is the number of bytes read (zero indicates
signal
.
Alternatively, -1 is returned when an error occurs, in such a case
errno
is set appropriately and further it is left unspecified whether the file position (if any) changes.
See also
References
External links
C_Programming/C_Reference/stdio.h/fread at Wikibooks
