Write (system call)

In this article, we are going to explore Write (system call) and its impact on our current society. Write (system call) is a topic that has sparked the interest of many experts in the field, as well as the general population. Over the years, Write (system call) has been the subject of numerous studies and investigations, which have allowed us to better understand its implications and consequences in different areas. From its origin to its current effects, Write (system call) has played a large role in shaping our reality, and it is crucial to analyze it from different perspectives to understand its full scope. In this sense, this article aims to unravel the most relevant aspects of Write (system call), as well as discuss its importance and relevance today.


The write is one of the most basic routines provided by a Unix-like operating system kernel. It writes data from a buffer declared by the user to a given device, such as a file. This is the primary way to output data from a program by directly using a system call. The destination is identified by a numeric code. The data to be written, for instance a piece of text, is defined by a pointer and a size, given in number of bytes.

write thus takes three arguments:

  1. The file code (file descriptor or fd).
  2. The pointer to a buffer where the data is stored (buf).
  3. The number of bytes to write from the buffer (nbytes).

POSIX usage

The write call interface is standardized by the POSIX specification. Data is written to a file by calling the write function. The function prototype is: 

 ssize_t write(int fildes, const void *buf, size_t nbyte);
Argument Description
fildes
 The file descriptor obtained from a call to open(). It is an integer value. The values 0, 1, 2 can also be given, for standard input, standard output & standard error, respectively .
buf
 Points to a character array, with content to be written to the file pointed to by filedes.
nbyte
 Specifies the number of bytes to be written from the character array, buf, into the file pointed to by filedes.

In above syntax, ssize_t is a typedef. It is a signed data type defined in stddef.h. Note that write() does not return an unsigned value; it returns -1 if an error occurs so it must return a signed value.
The write function returns the number of bytes successfully written into the file, which may at times be less than the specified nbytes. It returns -1 if an exceptional condition is encountered, see section on errors below.

Linux

On linux, write is system call number 1

See also

References

  1. ^ http://www.unix.com/man-page/FreeBSD/2/write/ Manual page for Write
  2. ^ https://www.gnu.org/s/hello/manual/libc/I_002fO-Primitives.html#I_002fO-Primitives I/O Primitives
  3. ^ "Write".
  4. ^ https://github.com/torvalds/linux/blob/master/arch/x86/entry/syscalls/syscall_64.tbl

External links

Wikious
Boobota
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