错误：分配给类型 'BusRoute' {aka 'struct 时的类型不兼容<anonymous> '} 来自类型 'void *'</anonymous>

Question

I created a typedef struct named BusRoute and a pointer to an array of BusRoute named ActiveBusRoutes.

typedef struct 
{
    unsigned int busRouteNumber;
    char* startingLocation;
    char* endingLocation;
    Time routeStartTime;
    Time routeEndTime;
}BusRoute;



BusRoute* ActiveBusRoutes[100];

And I need a function to detect 'empty' elements in the ActiveBusRoutes array, ie wherever the pointer is NULL.

BusRoute* loopBus(){
    BusRoute* br; BusRoute* start=*ActiveBusRoutes;
    for( br=start; br<start + 100; br++){
        if(*br= NULL){
            return br;
            exit;
        }
    }
}

When I use gcc to check, it report error, how to fix it plz

 error: incompatible types when assigning to type ‘BusRoute’ {aka ‘struct <anonymous>’} from type ‘void *’
   78 |         if((*br)= NULL){

Answer 1

= means assignment and the code is trying to assign NULL where it shouldn't.

== means test for equality.

With a change, this will serve you better, but always ends on the first found empty slot in the array.

BusRoute **loopBus() {
    const int nRoutes = sizeof ActiveBusRoutes/sizeof ActiveBusRoutes[0];
    for( int i = 0; i < nRoutes; i++ )
        if( ActiveBusRoutes[ i ] == NULL )
            return &ActiveBusRoutes[ i ]; // ptr to empty spot in array

    return NULL; // No empty spots; all are used
}

EDIT: Now returns non-NULL pointer to first empty slot, or returns NULL if there are no empty spots... Notice function declaration.