The close() system call closes an open file descriptor, freeing it for subsequent reuse by the process. When a process terminates, all of its open file descriptors are automatically closed.
#include <unistd.h>
int close(int fd);Returns 0 on success, or -1 on error
It is usually good practice to close unneeded file descriptors explicitly, since this makes our code more readable and reliable in the face of subsequent modifications. Furthermore, file descriptors are a consumable resource, so failure to close a file descriptor could result in a process running out of descriptors. This is a particularly important issue when writing long-lived programs that deal with multiple files, such as shells or network servers.
Just like every other system call, a call to close() should be bracketed with error-checking code, such as the following:
if (close(fd) == -1)
errExit("close");This catches errors such as attempting to close an unopened file descriptor or close the same file descriptor twice, and catches error conditions that a specific file system may diagnose during a close operation.
NFS (Network File System) provides an example of an error that is specific to a file system. If an NFS commit failure occurs, meaning that the data did not reach the remote disk, then this error is propagated to the application as a failure in the close() call.