Available memory for iPhone OS app

Is there a function or constant defining the amount of available memory for an app in iPhone OS?

I'm looking for a device-开发者_JS百科independent way (iPod touch, iPhone, iPad) to know how much memory the app has left.

This function will return the available memory in bytes:

#import <mach/mach.h> 
#import <mach/mach_host.h>

natural_t  freeMemory(void) {
    mach_port_t           host_port = mach_host_self();
    mach_msg_type_number_t   host_size = sizeof(vm_statistics_data_t) / sizeof(integer_t);
    vm_size_t               pagesize;
    vm_statistics_data_t     vm_stat;

    host_page_size(host_port, &pagesize);

    if (host_statistics(host_port, HOST_VM_INFO, (host_info_t)&vm_stat, &host_size) != KERN_SUCCESS) NSLog(@"Failed to fetch vm statistics");

    natural_t   mem_used = (vm_stat.active_count + vm_stat.inactive_count + vm_stat.wire_count) * pagesize;
    natural_t   mem_free = vm_stat.free_count * pagesize;
    natural_t   mem_total = mem_used + mem_free;

    return mem_free;
}

There is no defined maximum amount of memory that an iPhone app can use. Whether your app will be terminated due to lack of memory depends on whatever algorithms the OS is using and what other apps happen to be using memory at the same time (safari, mail, etc.).

The following Swift function will return the system's free memory (RAM) in bytes. It will return nil on failure.

func systemFreeMemorySize() -> UInt?
{
    let HOST_VM_INFO_COUNT: mach_msg_type_number_t = mach_msg_type_number_t(sizeof(vm_statistics_data_t) / sizeof(integer_t))

    let host: host_t = mach_host_self()

    var pageSize: vm_size_t = vm_size_t()
    let hostPageSizeKernStatus: kern_return_t = host_page_size(host, &pageSize)
    guard hostPageSizeKernStatus == KERN_SUCCESS else {
        NSLog("Error with host_page_size(): " + (String.fromCString(mach_error_string(hostPageSizeKernStatus)) ?? "unknown error"))
        return nil
    }

    var stats: vm_statistics_data_t = vm_statistics_data_t()
    var count: mach_msg_type_number_t = HOST_VM_INFO_COUNT

    let kernStatus: kern_return_t = withUnsafeMutablePointer(&stats) {
        return host_statistics(host, HOST_VM_INFO, host_info_t($0), &count)
    }

    guard kernStatus == KERN_SUCCESS else {
        NSLog("Error with host_statistics(): " + (String.fromCString(mach_error_string(kernStatus)) ?? "unknown error"))
        return nil
    }

    return UInt(stats.free_count) * UInt(pageSize)
}