init commit

3sem/cnts/contest4/03.c

@@ -0,0 +1,118 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/file.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <limits.h>
+#include <errno.h>
+
+enum
+{
+    ARGS_NUM = 2,
+};
+
+int
+safe_read(int fd, void *buf, size_t count)
+{
+    errno = 0;
+    size_t bytes_read = 0;
+    while (bytes_read < count) {
+        ssize_t res = read(fd, buf + bytes_read, count - bytes_read);
+
+        if (res < 0) {
+            if (errno == EINTR) {
+                errno = 0;
+                continue;
+            }
+
+            fprintf(stderr, "Error reading from file descriptor %d\n", fd);
+            close(fd);
+            exit(1); // TODO: по-хорошему заменить на внешний обработчик ошибок
+        }
+
+        if (res == 0) {
+            break;
+        }
+
+        bytes_read += res;
+    }
+
+    return bytes_read;
+}
+
+int
+safe_write(int fd, void *buf, size_t count)
+{
+    errno = 0;
+    size_t bytes_written = 0;
+    while (bytes_written < count) {
+        ssize_t res = write(fd, buf + bytes_written, count - bytes_written);
+
+        if (res < 0) {
+            if (errno == EINTR) {
+                errno = 0;
+                continue;
+            }
+
+            fprintf(stderr, "Error writing to file descriptor %d\n", fd);
+            close(fd);
+            exit(1); // TODO: по-хорошему заменить на внешний обработчик ошибок
+        }
+
+        bytes_written += res;
+    }
+
+    return bytes_written;
+}
+
+int
+main(int argc, char *argv[])
+{
+    if (argc != ARGS_NUM) {
+        fprintf(stderr, "Wrong number of arguments\n");
+        return 1;
+    }
+
+    int fd = open(argv[1], O_RDWR);
+    if (fd == -1) {
+        fprintf(stderr, "Error opening file %s\n", argv[1]);
+
+        return 1;
+    }
+
+    long long num, min_num = LLONG_MAX;
+    off_t pt_min = -1;
+
+    while (safe_read(fd, &num, sizeof(num)) == sizeof(num)) {
+        if (num < min_num || pt_min == -1) {
+            min_num = num;
+
+            if ((pt_min = lseek(fd, 0, SEEK_CUR) - sizeof(num)) == -1) {
+                fprintf(stderr, "Error in navigate file %s\n", argv[1]);
+
+                return 1;
+            }
+        }
+    }
+
+    if (min_num != LLONG_MIN && pt_min != -1) {
+        min_num = -min_num;
+        if (lseek(fd, pt_min, SEEK_SET) == -1) {
+            fprintf(stderr, "Error in navigate file %s\n", argv[1]);
+
+            return 1;
+        }
+
+        if (safe_write(fd, &min_num, sizeof(min_num)) != sizeof(num)) {
+            printf("Error while writing");
+
+            return 1;
+        }
+    }
+
+    close(fd);
+
+    return 0;
+}