#include <stdio.h> #include <fcntl.h> #include <unistd.h> #include <errno.h> #include <string.h> void print_error(const char *msg) { printf("%sn", msg); printf(" errno = %dn", errno); printf(" strerror = %snn", strerror(errno)); } int main(void) { int fd; ssize_t bytes; /* 1. open() failure: file does not exist */ fd = open("this_file_does_not_exist.txt", O_RDONLY); if (fd == -1) { print_error("open() failed (nonexistent file)"); } /* 2. write() failure: invalid file descriptor */ bytes = write(-1, "hello", 5); if (bytes == -1) { print_error("write() failed (invalid file descriptor)"); } /* 3. open() failure: permission denied (likely) */ fd = open("/root/secret.txt", O_WRONLY); if (fd == -1) { print_error("open() failed (permission denied)"); } /* 4. write() failure: writing to read-only file */ fd = open("readonly.txt", O_RDONLY | O_CREAT, 0444); if (fd != -1) { bytes = write(fd, "test", 4); if (bytes == -1) { print_error("write() failed (read-only file)"); } close(fd); } return 0; }