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A simple way to detect at runtime if we're running in UIKit legacy mode or the new "flat" variant. Written for our PDF iOS SDK (, where the precompiled binary needs to detect at runtime in what variant it's running. Want more stuff like that? Follow me on Twitter:
// Taken from This snippet is under public domain.
#define UIKitVersionNumber_iOS_7_0 0xB57
BOOL PSPDFIsUIKitFlatMode(void) {
static BOOL isUIKitFlatMode = NO;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
// We get the modern UIKit if system is running >= iOS 7 and we were linked with >= SDK 7.
if (kCFCoreFoundationVersionNumber >= kCFCoreFoundationVersionNumber_iOS_7_0) {
isUIKitFlatMode = (NSVersionOfLinkTimeLibrary("UIKit") >> 16) >= UIKitVersionNumber_iOS_7_0;
return isUIKitFlatMode;
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nzhuk commented Oct 30, 2013

How about [[NSBundle mainBundle] objectForInfoDictionaryKey:@"DTSDKName"] ? Xcode injects that key into app's Info.plist during compilation, and it contains the name of Base SDK (e.g. "iphoneos6.1" or "iphonesimulator6.1").

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Looks like this doesn't work anymore as of iOS 7.1b2. I've updated the code for a new way that works.

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NSVersionOfLinkTimeLibrary seems to be the most stable solution. Are those version numbers defined somewhere, or should I just use them as magic constants?

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Check the dyld(3) man page:

NSVersionOfLinkTimeLibrary(const char* libraryName);

NSVersionOfLinkTimeLibrary() returns the current_version number that the main executable was linked
against at build time.  The libraryName parameter would be "bar" for /path/libbar.3.dylib and "Foo" for
/path/Foo.framework/Versions/A/Foo.  This function returns -1 if the main executable did not link
against the specified library.

They're just whatever number the team for that library uses.

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0xced commented Dec 15, 2013

In order to check which SDK version was used to build a binary, UIKit uses the _UIApplicationLinkedOnOrAfter function. It is implemented by comparing the major version of UIKit at link time (NSVersionOfLinkTimeLibrary("UIKit") >> 16) to a value in the __UIKitVersionNumbers table.

Here is this UIKit version numbers table, built by running otool -L on UIKit of all these iOS versions (yes I have a huge archive!):

IndexiOS VersionHexadecimalDecimal

Weirdly enough, the __UIKitVersionNumbers contains 0x2EC instead of 0x2EB for iPhone OS 2.1. But since nobody cares at all about iPhone OS 2 this should not be a problem.

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nacho4d commented Dec 16, 2013

Awesome thread!

One tiny thing to add:

If kCFCoreFoundationVersionNumber_iOS_7_0 is undefined, use following snippet:

ifndef kCFCoreFoundationVersionNumber_iOS_7_0

define kCFCoreFoundationVersionNumber_iOS_7_0 847.2


Instead of the defining the var I would use the & ... like

if (&kCFCoreFoundationVersionNumber_iOS_7_0 &&
    kCFCoreFoundationVersionNumber >= kCFCoreFoundationVersionNumber_iOS_7_0) 
{ ...

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bgglenn commented Oct 2, 2014

For anyone googling their way here, 8.0 is 0xCF6.

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steipete commented Aug 5, 2016

iOS 9.3: 0xDB8
iOS 10b4: 0xE0C

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steipete commented Oct 1, 2018

For iOS 12 (GM), it seems that casting to unsigned integer is now required:

(lldb) p (int32_t)NSVersionOfLinkTimeLibrary("UIKit") >> 16
(int32_t) $4 = -4536
(lldb) p (uint32_t)NSVersionOfLinkTimeLibrary("UIKit") >> 16
(uint32_t) $5 = 61000

-> UIKitVersionNumber_iOS_12_0 = 0xEE48

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clementbarry commented Sep 30, 2021

iOS 15.0 is 0x13CB

(lldb) p (uint32_t)NSVersionOfLinkTimeLibrary("UIKit") >> 16
(uint32_t) $2 = 5067

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iOS 15.2 is 0x1455

(lldb) p (uint32_t)NSVersionOfLinkTimeLibrary("UIKit") >> 16
(uint32_t) $1 = 5205

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