How do I close a file descriptor in C?
To close a file descriptor, we use the close system call. Here’s an example:
#include <unistd.h>
#include <assert.h>
#include <stdio.h>
#define WRITE(F, S) write((F), (S), sizeof(S))
int main(void) {
// Do some normal writing.
assert(0 < WRITE(1, "This is written to stdout via descriptor 1\n"));
// Get another reference to the same stdout pipe.
int new_stdout = dup(1);
// Writing to the new reference also works.
assert(0 < WRITE(new_stdout, "This is written to stdout via new descriptor\n"));
// Close our original file descriptor to stdout!
close(1);
// Writing to our new reference still works.
// The pipe is only closed when all references to it are closed.
assert(0 < WRITE(new_stdout, "This is also written to stdout via new descriptor\n"));
// Close our final reference to the stdout pipe.
// This closes the write end of the pipe.
close(new_stdout);
// Now we can't write to the pipe, because the write end of the pipe has been closed.
assert(-1 == WRITE(new_stdout, "This should break\n"));
perror("Could not write to new_stdout");
return 0;
}
Tagged . All content copyright James Fisher 2017. This post is not associated with my employer.
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