z3 C++ API & ite

Question

Maybe I missed something, but what is the way of constructing an if-then-else expression using the z3 C++ API ?

I could use the C API for that, but I'm wondering why there is no such function in the C++ API.

regards, Julien

Answer 1

We can mix the C and C++ APIs. The file examples/c++/example.cpp contains an example using the C API to create the if-then-else expression. The function to_expr is essentially wrapping a Z3_ast with the C++ "smart pointer" expr that automatically manages the reference counters for us.

void ite_example() {
    std::cout << "if-then-else example\n";
    context c;

    expr f    = c.bool_val(false);
    expr one  = c.int_val(1);
    expr zero = c.int_val(0);
    expr ite  = to_expr(c, Z3_mk_ite(c, f, one, zero));

    std::cout << "term: " << ite << "\n";
}

I just added the ite function to the C++ API. It will be available in the next release (v4.3.2). If you want you can add to the z3++.h file in your system. A good place to include is after the function implies:

/**
   \brief Create the if-then-else expression <tt>ite(c, t, e)</tt>

   \pre c.is_bool()
*/
friend expr ite(expr const & c, expr const & t, expr const & e) {
    check_context(c, t); check_context(c, e);
    assert(c.is_bool());
    Z3_ast r = Z3_mk_ite(c.ctx(), c, t, e);
    c.check_error();
    return expr(c.ctx(), r);
}

Using this function, we can write:

void ite_example2() {
    std::cout << "if-then-else example2\n";
    context c;
    expr b = c.bool_const("b");
    expr x = c.int_const("x");
    expr y = c.int_const("y");
    std::cout << (ite(b, x, y) > 0) << "\n";
}