Google Maps标记未显示javascript

我正在使用自定义地图上的标记进行挣扎。地图以正确的位置为中心，但标记未显示在该位置。有人已经解决了相同的问题吗？非常感谢您的帮助！

  function initialize() {
                var map_canvas = document.getElementById('map_canvas');
                var map_options = {
                    scrollwheel: false,
                    zoom: 16,
                    center: new google.maps.LatLng(51.840164,4.33244),
                    mapTypeId: google.maps.MapTypeId.ROADMAP,
                    mapTypeControl: false,
                    mapTypeControlOptions: {
                        style: google.maps.MapTypeControlStyle.HORIZONTAL_BAR,
                        position: google.maps.ControlPosition.TOP
                    },
                    panControl: false,
                    panControlOptions: {
                        position: google.maps.ControlPosition.TOP_RIGHT
                    },
                    zoomControl: true,
                    zoomControlOptions: {
                        style: google.maps.ZoomControlStyle.LARGE,
                        position: google.maps.ControlPosition.LEFT_CENTER
                    },
                    scaleControl: false,
                    scaleControlOptions: {
                        position: google.maps.ControlPosition.TOP_LEFT
                    },
                    streetViewControl: false,
                    streetViewControlOptions: {
                        position: google.maps.ControlPosition.LEFT_CENTER
                    }
                  }

                var map = new google.maps.Map(map_canvas, map_options)
              }

        function addMarker(feature) {
                  var marker = new google.maps.Marker({
                    position: feature.position,
                    icon: 'locationpointer.png',

                    map: map_canvas
                  });
                }

                var features = [
                  {
                    position: new google.maps.LatLng(51.840164,4.33244),
                  }
                ];

                for (var i = 0, feature; feature = features[i]; i++) {
                  addMarker(feature);
                }




        google.maps.event.addDomListener(window, 'load', initialize);