gtk How to highlight the next line of textview? -

i have highlight second line (arr[ii+1]). i'm tryng remove previous tag 2 iterators , add highlight new line others 1 :

                                sprintf(buffers,"%s",arr[ii]);                              if(cuno==0)                             {                                gtk_text_buffer_get_end_iter(buffer, &ei);                                gtk_text_buffer_insert(buffer, &ei, buffers, -1);                                gtk_text_buffer_get_end_iter(buffer, &ei);                                gtk_text_buffer_insert(buffer, &ei, "\n", -1);                                cuno++;                             }                                 sprintf(buffers2,"%s",arr[ii+1]);                                  gtk_text_buffer_create_tag(buffer, "gray_bg","background", "gray", null);                                gtk_text_buffer_get_end_iter(buffer, &ei2);                                gtk_text_buffer_get_end_iter(buffer, &ei);                                gtk_text_buffer_insert(buffer, &ei2, buffers2, -1);                                gtk_text_buffer_get_end_iter(buffer, &ei2);                                gtk_text_buffer_insert(buffer, &ei2, "\n", -1);                                gtk_text_buffer_get_start_iter(buffer, &si2);                                gtk_text_buffer_get_start_iter(buffer, &si);                                gtk_text_buffer_remove_all_tags(buffer,&si, &ei);                                gtk_text_buffer_apply_tag_by_name(buffer, "gray_bg",&si2, &ei2); 

but on output text ever highlighted, can me?thank you

resolved one, thank :)

   gtk_text_buffer_create_tag(buffer, "gray_bg","background", "green", null);    gtk_text_buffer_get_iter_at_line(buffer,&si,ii+1);    gtk_text_buffer_get_iter_at_line_offset (buffer,&ei2,ii+1,lstr);    gtk_text_buffer_remove_tag_by_name (buffer,"gray_bg",&start,&end);    gtk_text_buffer_apply_tag_by_name(buffer, "gray_bg",&si, &ei2);