Check file handle in C using system calls

chp2/fread.c

@@ -0,0 +1,55 @@
+#include <errno.h>
+#include <fcntl.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int main(void) {
+  printf("Try to open file read.txt\n");
+  int fd = open("read.txt", O_RDONLY);
+  if (fd == -1) {
+    perror("Failed to open read.txt");
+    return -1;
+  }
+  printf("Open file success\n");
+
+  int len;
+  if ((len = lseek(fd, 0, SEEK_END)) == -1) {
+    perror("Failed to move cursor at end of read.txt file");
+    return -1;
+  }
+  printf("File size of %d bytes\n", len);
+  if (lseek(fd, 0, SEEK_SET) == -1) {
+    perror("Failed to move cursor at start of read.txt file");
+    return -1;
+  }
+
+  printf("Reading file read.txt\n");
+  char buf[len + 1];
+  memset(buf, 0, sizeof(buf));
+
+  size_t bytes_read_total = 0;
+  ssize_t ret;
+  while (bytes_read_total < len && (ret = read(fd, buf + bytes_read_total, len - bytes_read_total)) != 0) {
+    if (ret == -1) {
+      if (errno == EINTR) continue;
+      perror("Failed to read read.txt");
+      break;
+    }
+    bytes_read_total += ret;
+  }
+
+  buf[bytes_read_total] = '\0';
+
+  printf("File text is:\n\"%s\"\n", buf);
+
+  printf("Close file read.txt\n");
+  
+  if (close(fd) == -1) {
+    perror("Failed to close read.txt");
+    return -1;
+  }
+
+  return 0;
+}