[MSVC] convert unsigned to signed before applying unary minus

This should avoid the following:
  warning C4146: unary minus operator applied to unsigned type,
                 result still unsigned

diff --git a/src/xbt/xbt_log_appender_file.c b/src/xbt/xbt_log_appender_file.c
index d06d9b9..5342776 100644 (file)
--- a/src/xbt/xbt_log_appender_file.c
+++ b/src/xbt/xbt_log_appender_file.c
@@ -105,7 +105,7 @@ static void append2_file(xbt_log_appender_t this_, char *str) {
    fputs(str, d->file);
    if(d->count<0){
           fputs(APPEND2_END_TOKEN,d->file);
-          fseek(d->file,-strlen(APPEND2_END_TOKEN),SEEK_CUR);
+          fseek(d->file,-((signed long)strlen(APPEND2_END_TOKEN)),SEEK_CUR);
    }
 }