querybypoint using c++

[sch]

hi,
in my project, i want to query road name from shape file using c++ and
mapserver 4.8.4's lib, but i get Segment fault error every time, does
anybody have an example?
the code i used is here:

int main()
{
    printf("main function.\n");

    mapObj  *map = NULL;
    char    *mapfile = "/home/www/mapserver/gmap/htdocs/china_pg.map";

    map = msLoadMap(mapfile, NULL);
    if(!map) {
        printf("msLoadMap error.\n");
        msWriteError(stderr);
        exit(0);
    }

    int status = msMapSetExtent(map, 73.81367424697862, 17.620038368633608,
134.3885088548217, 55.14595792129112);
    pointObj point = {111.12, 34.76};

   msQueryByPoint(map, -1, MS_SINGLE, point, -1);

    msFreeMap(map);
    msCleanup();

    return 1;
}

by the way, the os i used is Redhat3.0. when i use php-mapscript to query,
it's ok.
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