+/*
+ Read exactly one line and strip the trailing newline if any. If the
+ file was on EOF, return NULL. Otherwise, return all the data in a
+ dynamically allocated buffer.
+*/
+char *readline(FILE *fp)
+{
+ char *newline = NULL;
+ char *p;
+ char *line; /* The array that contains everything that has been read
+ so far */
+ char *idx; /* Read into this pointer, which points to an offset
+ within line */
+ size_t size, newsize; /* The size of the current array pointed to by
+ line */
+ size_t maxlen; /* Maximum number of characters that may be read with
+ fgets. This is newsize - oldsize. */
+
+ if(feof(fp))
+ return NULL;
+
+ size = 100;
+ maxlen = size;
+ line = xmalloc(size);
+ idx = line;
+ for(;;)
+ {
+ errno = 0;
+ p = fgets(idx, maxlen, fp);
+ if(p == NULL) /* EOF or error */
+ {
+ if(feof(fp))
+ break;
+
+ /* otherwise: error; let the calling function print an error
+ message if applicable */
+ free(line);
+ return NULL;
+ }
+
+ newline = strchr(p, '\n');
+ if(newline == NULL)
+ /* We haven't yet read everything to the end of the line */
+ {
+ newsize = size << 1;
+ line = xrealloc(line, newsize);
+ idx = &line[size - 1];
+ maxlen = newsize - size + 1;
+ size = newsize;
+ }
+ else
+ {
+ *newline = '\0'; /* kill newline */
+ break; /* yay */
+ }
+ }
+
+ return line;
+}
+