dot_polygon: take a const pointer for a string that is not modified

diff --git a/cmd/gvmap/make_map.c b/cmd/gvmap/make_map.c
index 53e9926dfe6e849e28a9b8f1a419f3cf6c612a9e..262bc63b6c2b7856c034b822db126bde92a325f1 100644 (file)
--- a/cmd/gvmap/make_map.c
+++ b/cmd/gvmap/make_map.c
@@ -245,7 +245,7 @@ static void plot_dot_labels(FILE *f, int n, int dim, real *x, char **labels, flo
 }
 
 static void dot_polygon(agxbuf *sbuff, int np, float *xp, float *yp, real line_width,  
-                       int fill, char *cstring){
+                        int fill, const char *cstring){
 
   if (np > 0){
     if (fill >= 0){