deque.push_front() giving error "expression must have class type"

Question

I am trying to initialize a deque with pointers to a user defined struct, Tile, in order to eliminate unnecessary copying.

My code looks like this:

Tile *start = new Tile(0,0,0, 'q', nullptr);
deque<Tile*> search();
search.push_front(start);

The above code is located in main.cpp.

The Tile struct looks like this, and is contained in hunt.h:

struct Tile
{
    int row; int col; int farm;
    char tile;
    Tile * added_me;

    Tile(int f, int r, int c, char t, Tile * a) :
        farm(f), row(r), col(c), tile(t), added_me(a){}
};

The layout of my program is as follows:

main.cpp: includes "io.h"

io.h: includes "hunt.h", various standard libraries

hunt.h: includes vector, deque, Tile struct

However, I am getting an error in main.cpp when I try to push_front(start): expression must have class type." I wasn't sure if a possible fault in my #includes was causing this error, so please let me know if this is the case. Otherwise, I am not entirely sure how to fix this error.

Thanks in advance!

Answer 1

When you write

deque<Tile*> search();

you aren't actually declaring a deque<Tile*> named search and using the default constructor. Instead, C++ interprets this as a function declaration for a function named search that takes no parameters and returns a deque<Tile*>. You can't call push_front on a function, hence the error.

To fix this, either remove the () from the declaration of the variable, or replace them with {} (if you're using a C++11-compliant compiler). That will cause C++ to (correctly) interpret that you want to declare a variable.

Hope this helps!