C code to swift conversion

Question

I am trying to convert below code to Swift:

{
    // Set up the variables
    double totalUsedMemory = 0.00;
    mach_port_t host_port;
    mach_msg_type_number_t host_size;
    vm_size_t pagesize;

    // Get the variable values
    host_port = mach_host_self();
    host_size = sizeof(vm_statistics_data_t) / sizeof(integer_t);
    host_page_size(host_port, &pagesize);

    vm_statistics_data_t vm_stat;

    // Check for any system errors
    if (host_statistics(host_port, HOST_VM_INFO, (host_info_t)&vm_stat, &host_size) != KERN_SUCCESS) {
        // Error, failed to get Virtual memory info
        return -1;
    }

    // Memory statistics in bytes
    natural_t usedMemory = (natural_t)((vm_stat.active_count +
                            vm_stat.inactive_count +
                            vm_stat.wire_count) * pagesize);
    natural_t allMemory = [self totalMemory];


    return usedMemory;
}

My Swift code is:

{
    // Set up the variables
    var totalUsedMemory: Double = 0.00
    var host_port: mach_port_t
    var host_size: mach_msg_type_number_t
    var pagesize:vm_size_t

    // Get the variable values
     host_port = mach_host_self()

    host_size = mach_msg_type_number_t(MemoryLayout<vm_statistics_data_t>.stride / MemoryLayout<integer_t>.stride)

    //                host_size = sizeof(vm_statistics_data_t) / sizeof(integer_t);
    host_page_size(host_port, &pagesize);

    var vm_stat: vm_statistics_data_t ;

    // Check for any system errors
    if (host_statistics(host_port, HOST_VM_INFO, (host_info_t)&vm_stat, &host_size) != KERN_SUCCESS) {
        // Error, failed to get Virtual memory info
        return -1;
    }
    // Memory statistics in bytes
    var usedMemory: Int64  = (Int64)((vm_stat.active_count + vm_stat.inactive_count + vm_stat.wire_count) * pagesize);

    return usedMemory;
}

I am getting these 2 errors:

**Binary operator '&' cannot be applied to operands of type '(host_info_t).Type' (aka 'UnsafeMutablePointer.Type') and 'vm_statistics_data_t' (aka 'vm_statistics')

in this statement host_statistics(host_port, HOST_VM_INFO, (host_info_t)&vm_stat, &host_size)

And

Binary operator '*' cannot be applied to operands of type 'UInt32' and 'vm_size_t' (aka 'UInt')**

in this statement - var usedMemory: Int64 = (Int64)((vm_stat.active_count + vm_stat.inactive_count + vm_stat.wire_count) * pagesize);

Answer 1

Swift is a lot more strict about pointer types than C is, which can make it a real pain to interact with functions like this that expect you to pass pointers to types other than the actual type of the thing you're trying to pass to the function. So I agree with the commenters that you're probably better off leaving this function in (Objective-)C. However, if you absolutely have to convert to Swift, you're probably going to have to do something like this:

// Initialize a blank vm_statistics_data_t
var vm_stat = vm_statistics_data_t()

// Get a raw pointer to vm_stat
let err: kern_return_t = withUnsafeMutableBytes(of: &vm_stat) {
    // Bind the raw buffer to Int32, since that's what host_statistics
    // seems to want a pointer to.
    let boundBuffer = $0.bindMemory(to: Int32.self)

    // Call host_statistics, and return its status out of the closure.
    return host_statistics(host_port, HOST_VM_INFO, boundBuffer.baseAddress, &host_size)
}

// Now take a look at what we got and compare it against KERN_SUCCESS
if err != KERN_SUCCESS {
    // Error, failed to get Virtual memory info
    return -1;
}