Reorganized read_file loop.

ChangeLog

 2012-09-10  Niels Möller  <nisse@lysator.liu.se>
 
+	* examples/io.c (read_file): Explicitly treat an empty file as an
+	error. Rearrange loop, check for short fread return value.
+
 	* desdata.c: Don't declare printf, include <stdio.h> instead. Also
 	deleted casts of printf return value.
 

examples/io.c

@@ -71,8 +71,7 @@ werror(const char *format, ...)
 unsigned
 read_file(const char *name, unsigned max_size, char **contents)
 {
-  unsigned size;
-  unsigned done;
+  unsigned size, done;
   char *buffer;
   FILE *f;
     
@@ -82,21 +81,10 @@ read_file(const char *name, unsigned max_size, char **contents)
       werror("Opening `%s' failed: %s\n", name, strerror(errno));
       return 0;
     }
-  buffer = NULL;
 
-  if (max_size && max_size < 100)
-    size = max_size;
-  else
-    size = 100;
-
-  /* FIXME: The use of feof and ferror in this loop is a bit confused
-     (but I think it is still correct). We should check the return
-     value of fread, and call feof and/or ferror when we get a short
-     item count. */	
+  size = 100;
 
-  for (done = 0;
-       (!max_size || done < max_size) && !feof(f);
-       size *= 2)
+  for (buffer = NULL, done = 0;; size *= 2)
     {
       char *p;
 
@@ -118,8 +106,25 @@ read_file(const char *name, unsigned max_size, char **contents)
       buffer = p;
       done += fread(buffer + done, 1, size - done, f);
 
-      if (ferror(f))
-	goto fail;
+      if (done < size)
+	{
+	  /* Short count means EOF or read error */
+	  if (ferror(f))
+	    {
+	      fprintf (stderr, "Reading `%s' failed: %s\n",
+		       name, strerror(errno));
+
+	      goto fail;
+	    }
+	  if (done == 0)
+	    /* Treat empty file as error */
+	    goto fail;
+
+	  break;
+	}
+
+      if (size == max_size)
+	break;
     }
   
   fclose(f);

examples/io.h

@@ -39,8 +39,11 @@ xalloc(size_t size);
 void
 werror(const char *format, ...) PRINTF_STYLE(1, 2);
 
-/* If size is > 0, read at most that many bytes. If size == 0,
- * read until EOF. Allocates the buffer dynamically. */
+/* If size is > 0, read at most that many bytes. If size == 0, read
+ * until EOF. Allocates the buffer dynamically. An empty file is
+ * treated as an error; return value is zero, and no space is
+ * allocated. The returned data is NUL-terminated, for convenience. */
+
 unsigned
 read_file(const char *name, unsigned size, char **buffer);