I have a function uint32_t* GetArrayPointer() {} which returns a Pointer to an array of uint32. Later in my code I go through that array and do some calculation with the values. Now i want to mock the function in my test. So i do
MOCK_METHOD0(GetArrayPointer,uint32_t*())
And in my test
Uint32_t testArray[6] = {...}
EXPECT_CALL(mockObject,GetArrayPointer()).WillRepeatedly(Return(testArray));
FunctionCall()...
But with this code I get a segfault.
How can I return the Pointer to my testArray?
The code looked fine for returning the array as a pointer, since the array will decay into a pointer when passing it as an argument to the function.
I am guessing that the function uint32_t* GetArrayPointer() is a global function, which the function mocking is not allowed, we need to create a wrapper function to wrap it.
Related link:
How can I effectively test against the Windows API?
Related
How can I pass property getter to a function that accepts function type?
Here is an example of what I want achieve:
class Test {
val test: String
get() = "lol"
fun testFun(func: ()->String) {
// invoke it here
}
fun callTest() {
testFun(test::get)
// error: Type mismatch: inferred type is
// KFunction1<#ParameterName Int, Char> but () -> String was expected
}
}
Is there a way?
You can reference the getter by writing ::test (or this::test).
When you write test::get, you are actually referencing the get method on String. That method takes an index and returns the character at that index.
If the property was a var and you want a reference to its setter, you can write ::test::set.
For more info on property references, see here: https://kotlinlang.org/docs/reference/reflection.html#bound-function-and-property-references-since-11
As already mentioned, you can use this::test to refer to the getter. Alternatively, if you have kotlin-reflect, you can do this::test.getter.
When you pass the field as a function, it assumes you mean the getter. As a result, if you want the setter, you have two options:
this::test::set
or
this::test.setter
The latter, just like this::test.getter requires kotlin-reflect, or the program will crash (tested locally with Kotlin 1.2.50)
You can, however, get the getter in another way. But I recommend you just stick with this::test because it's shorter.
You can do:
this::something::get
With just something::get it refers to the method inside the String class, which returns a char at an index. For reference, the method declaration:
public override fun get(index: Int): Char
If you don't mind, just use { test } (e.g. testFun { test }). This will exactly translate to your () -> String. The next best alternative is probably ::test (or this::test) as was already mentioned.
The second has probably only minor (negligible?) impact on performance. I did not test it myself, nor did I found any source which tells something regarding it. The reason why I say this, is how the byte code underneath looks like. Just due to this question I asked myself about the difference of the two: Is the property reference (::test) equivalent to a function accessing the property ({ test }) when passed as argument e.g. `() -> String`?
It seems that you are doing something wrong on logical level.
If you are overriding get method of a variable, then you can access it's value through this get method. Thus, why bother with test::get (which is totally different method, by the way, all you are doing is trying to access char from string), when you can just access variable by it's name?
I am attempting a method swizzle in Obj-C but I would like to pass it a pure C function. This means I need to somehow assign a selector and/or manually build an objc_method struct. Maybe somehow leverage NSInvocation?
My understanding is that due to the fact that Obj-C is a strict superset of C and therefor fully compatible.
What I have going now:
main.m :
#include....
CFStringRef strRet(void) {
return CFSTR("retString");
}
int main(int argc, const char * argv[]) {
#autoreleasepool {
SEL _strRet = sel_registerName("strRet");
//I also tried: SEL _strRet = NSSelectorFromString(#"strRet");
Class bundle = objc_getClass("NSBundle");
method_exchangeImplementations(
class_getInstanceMethod(bundle, sel_registerName("anySelector")),
class_getInstanceMethod(bundle, sel_registerName("_strRet")
);
I have tried putting the C function inside #implementation (which I would like to avoid) and even then it did not work.
You can't swizzle a C function per se; swizzling is based on method lookup which goes through method descriptions (which are represented by the Method type by the runtime functions) and C functions do not have a method description.
However the implementation of a method is just a C function. Such a C function must take a minimum of two arguments, being the object the method is invoked on (the Objective-C implicit parameter self) and the selector (the Objective-C implicit parameter _cmd). When you swizzle a method the replacement implementation, a C function, must have exactly the same type as the original – complete with the two implicit arguments – so your strRet() would not be suitable as is, you would need to change it to:
CFStringRef strRet(NSObject *self, CMD sel, void)
{
return CFSTR("retString");
}
So you have three main choices:
The easiest way is to define a method whose body is your "pure" C function, then swizzle the recommended way (taking care to handle inheritance correctly, see this answer).
If you really want to write a C function and that C function does not need to call the original implementation of the method then:
(a) You need to convert your C function into one which can be used as a method implementation. You can:
If you are writing/have the source of the C function you simply define it to take the two implicit arguments as above. Take the address of this function and cast it to IMP, which is just a typedef for a C function pointer of the appropriate type, for use below.
If you are using a C function whose definition you cannot change then you can do one of:
Write a C wrapper function which takes the extra arguments, ignores them and calls your target C function. Take the address of this wrapper function and cast it to IMP for use below.
Wrap the call to your C function in a block and use imp_implementationWithBlock() to produce an IMP value from it. You can read this article for a description of using imp_implementationWithBlock().
(b) use method_setImplementation() to set the implementation to the IMP value you produced in (a).
If you really want to write a C function and that C function does need to call the original implementation of the method then you will need to add a method to your class whose implementation is your C function – modified/wrapped as in (2), then swizzle your added method with your original method as under (1) so that the original implementation is still available as a method. To add a method you use class_addMethod()
HTH
The key here is finding a mechanism that maps between the function pointer and your context. The simplest way to do that is by generating a new function pointer. You can use imp_implementationWithBlock(), MABlockClosure, or roll your own.
The simplest mechanism to create a new function pointer I've found is to remap the entire function to a new address space. The new resulting address can be used as a key to the required data.
#import <mach/mach_init.h>
#import <mach/vm_map.h>
void *remap_address(void* address, int page_count)
{
vm_address_t source_address = (vm_address_t) address;
vm_address_t source_page = source_address & ~PAGE_MASK;
vm_address_t destination_page = 0;
vm_prot_t cur_prot;
vm_prot_t max_prot;
kern_return_t status = vm_remap(mach_task_self(),
&destination_page,
PAGE_SIZE*(page_count ? page_count : 4),
0,
VM_FLAGS_ANYWHERE,
mach_task_self(),
source_page,
FALSE,
&cur_prot,
&max_prot,
VM_INHERIT_NONE);
if (status != KERN_SUCCESS)
{
return NULL;
}
vm_address_t destination_address = destination_page | (source_address & PAGE_MASK);
return (void*) destination_address;
}
Note that page_count should be large enough to contain all of your original function. Also, remember to handle pages that aren't required anymore and note that it takes a lot more memory per invocation than MABlockClosure.
(Tested on iOS)
JXA, with its built-in ObjC bridge, exposes enumeration and constants from the Foundation framework automatically via the $ object; e.g.:
$.NSUTF8StringEncoding // -> 4
However, there are also useful CFString constants in lower-level APIs that aren't automatically imported, namely the kUTType* constants in CoreServices that define frequently-used UTI values, such as kUTTypeHTML for UTI "public.html".
While you can import them with ObjC.import('CoreServices'), their string value isn't (readily) accessible, presumably because its type is CFString[Ref]:
ObjC.import('CoreServices') // import kUTType* constants; ObjC.import('Cocoa') works too
$.kUTTypeHTML // returns an [object Ref] instance - how do you get its string value?
I have yet to find a way to get at the string at the heart of what's returned:
ObjC.unwrap($.kUTTypeHTML) doesn't work, and neither does ObjC.unwrap($.kUTTypeHTML[0]) (nor .deepUnwrap()).
I wonder:
if there's a native JXA way to do this that I'm missing.
otherwise, if there's away to use ObjC.bindFunction() to define bindings for CFString*() functions that can solve the problem, such as to CFStringGetCString() or CFStringGetCStringPtr(), but it's not obvious to me how to translate the ObjC signatures.
While I don't understand all implications, the following seems to work:
$.CFStringGetCStringPtr($.kUTTypeHTML, 0) // -> 'public.html'
# Alternative, with explicit UTF-8 encoding specification
$.CFStringGetCStringPtr($.kUTTypeHTML, $.kCFStringEncodingUTF8) // ditto
The kUTType* constants are defined as CFStringRef, and CFStringGetCStringPtr returns a CFString object's internal C string in the specified encoding, if it can be extracted "with no memory allocations and no copying, in constant time" - or NULL otherwise.
With the built-in constants, it seems that a C string (rather than NULL) is always returned, which - by virtue of C data types mapping onto JXA data types - is directly usable in JavaScript:
$.CFStringGetCStringPtr($.kUTTypeHTML, 0) === 'public.html' // true
For background information (as of OSX 10.11.1), read on.
JXA doesn't natively recognize CFString objects, even though they can be "toll-free bridged" to NSString, a type that JXA does recognize.
You can verify that JXA does not know the equivalence of CFString and NSString by executing $.NSString.stringWithString($.kUTTypeHTML).js, which should return a copy of the input string, but instead fails with -[__NSDictionaryM length]: unrecognized selector sent to instance.
Not recognizing CFString is our starting point: $.kUTTypeHTML is of type CFString[Ref], but JXA doesn't return a JS string representation of it, only [object Ref].
Note: The following is in part speculative - do tell me if I'm wrong.
Not recognizing CFString has another side effect, namely when invoking CF*() functions that accept a generic type (or Cocoa methods that accept a toll-free bridged CF* type that JXA is unaware of):
In such cases, if the argument type doesn't exactly match the invoked function's parameter type, JXA apparently implicitly wraps the input object in a CFDictionary instance, whose only entry has key type, with the associated value containing the original object.[1]
Presumably, this is why the above $.NSString.stringWithString() call fails: it is being passed the CFDictionary wrapper rather than the CFString instance.
Another case in point is the CFGetTypeID() function, which expects a CFTypeRef argument: i.e., any CF* type.
Since JXA doesn't know that it's OK to pass a CFStringRef argument as-is as the CFTypeRef parameter, it mistakenly performs the above-mentioned wrapping, and effectively passes a CFDictionary instance instead:
$.CFGetTypeID($.kUTTypeHTML) // -> !! 18 (CFDictionary), NOT 7 (CFString)
This is what houthakker experienced in his solution attempt.
For a given CF* function you can bypass the default behavior by using ObjC.bindFunction() to redefine the function of interest:
// Redefine CFGetTypeID() to accept any type as-is:
ObjC.bindFunction('CFGetTypeID', ['unsigned long', [ 'void *']])
Now, $.CFGetTypeID($.kUTTypeHTML) correctly returns 7 (CFString).
Note: The redefined $.CFGetTypeID() returns a JS Number instance, whereas the original returns a string representation of the underlying number (CFTypeID value).
Generally, if you want to know the specific type of a given CF* instance informally, use CFShow(), e.g.:
$.CFShow($.kUTTypeHTML) // -> '{\n type = "{__CFString=}";\n}'
Note: CFShow() returns nothing and instead prints directly to stderr, so you can't capture the output in JS.
You may redefine CFShow with ObjC.bindFunction('CFShow', ['void', [ 'void *' ]]) so as not to show the wrapper dictionary.
For natively recognized CF* types - those that map onto JS primitives - you'll see the specific type directly (e.g., CFBoolean for false); for unknown - and therefore wrapped - instances, you'll see the wrapper structure as above - read on for more.
[1] Running the following gives you an idea of the wrapper object being generated by JXA when passing an unknown type:
// Note: CFShow() prints a description of the type of its argument
// directly to stderr.
$.CFShow($.kUTTypeHTML) // -> '{\n type = "{__CFString=}";\n}'
// Alternative that *returns* the description as a JS string:
$.CFStringGetCStringPtr($.CFCopyDescription($.kUTTypeHTML), 0) // -> (see above)
Similarly, using the known-to-JXA equivalence of NSDictionary and CFDictionary,
ObjC.deepUnwrap($.NSDictionary.dictionaryWithDictionary( $.kUTTypeHTML ))
returns {"type":"{__CFString=}"}, i.e., a JS object with property type whose value is at this point - after an ObjC-bridge call roundtrip - a mere string representation of what presumably was the original CFString instance.
houthakker's solution attempt also contains a handy snippet of code to obtain the type name of a CF* instance as a string.
If we refactor it into a function and apply the necessary redefinition of CFGetTypeID(), we get the following, HOWEVER:
A hack is needed to make it return a value predictably (see comments and source code)
Even then a random character sometimes appears as the end of the string returned, such as CFString, rather than CFString.
If anyone has an explanation for why the hack is needed and where the random characters come from, please let me know. The issues may be memory-management related, as both CFCopyTypeIDDescription() and CFStringCreateExternalRepresentation() return an object that the caller must release, and I don't know whether/how/when JXA does that.
/*
Returns the type name of the specified CF* (CoreFoundation) type instance.
CAVEAT:
* A HACK IS EMPLOYED to ensure that a value is consistently returned f
those CF* types that correspond to JS primitives, such as CFNumber,
CFBoolean, and CFString:
THE CODE IS CALLED IN A TIGHT LOOP UNTIL A STRING IS RETURNED.
THIS SEEMS TO WORK WELL IN PRACTICE, BUT CAVEAT EMPTOR.
Also, ON OCCASION A RANDOM CHARACTER APPEARS AT THE END OF THE STRING.
* Only pass in true CF* instances, as obtained from CF*() function
calls or constants such as $.kUTTypeHTML. Any other type will CRASH the
function.
Example:
getCFTypeName($.kUTTypeHTML) // -> 'CFString'
*/
function getCFTypeName(cfObj) {
// Redefine CFGetTypeID() so that it accepts unkown types as-is
// Caution:
// * ObjC.bindFunction() always takes effect *globally*.
// * Be sure to pass only true CF* instances from then on, otherwise
// the function will crash.
ObjC.bindFunction('CFGetTypeID', [ 'unsigned long', [ 'void *' ]])
// Note: Ideally, we'd redefine CFCopyDescription() analogously and pass
// the object *directly* to get a description, but this is not an option:
// ObjC.bindFunction('CFCopyDescription', ['void *', [ 'void *' ]])
// doesn't work, because, since we're limited to *C* types, we can't describe
// the *return* type in a way that CFStringGetCStringPtr() - which expects
// a CFStringRef - would then recognize ('Ref has incompatible type').
// Thus, we must first get a type's numerical ID with CFGetTypeID() and then
// get that *type*'s description with CFCopyTypeIDDescription().
// Unfortunately, passing the resulting CFString to $.CFStringGetCStringPtr()
// does NOT work: it yields NULL - no idea why.
//
// Using $.CFStringCreateExternalRepresentation(), which yields a CFData
// instance, from which a C string pointer can be extracted from with
// CFDataGetBytePtr(), works:
// - reliably with non-primitive types such as CFDictionary
// - only INTERMITTENTLY with the equivalent types of JS primitive types
// (such as CFBoolean, CFString, and CFNumber) - why??
// Frequently, and unpredictably, `undefined` is returned.
// !! THUS, THE FOLLOWING HACK IS EMPLOYED: THE CODE IS CALLED IN A TIGHT
// !! LOOP UNTIL A STRING IS RETURNED. THIS SEEMS TO WORK WELL IN PRACTICE,
// !! BUT CAVEAT EMPTOR.
// Also, sometimes, WHEN A STRING IS RETURNED, IT MAY CONTAIN A RANDOM
// EXTRA CHAR. AT THE END.
do {
var data = $.CFStringCreateExternalRepresentation(
null, // use default allocator
$.CFCopyTypeIDDescription($.CFGetTypeID(cfObj)),
0x08000100, // kCFStringEncodingUTF8
0 // loss byte: n/a here
); // returns a CFData instance
s = $.CFDataGetBytePtr(data)
} while (s === undefined)
return s
}
You can coerce a CF type to an NS type by first re-binding the CFMakeCollectable function so that it takes 'void *' and returns 'id', and then using that function to perform the coercion:
ObjC.bindFunction('CFMakeCollectable', [ 'id', [ 'void *' ] ]);
var cfString = $.CFStringCreateWithCString(0, "foo", 0); // => [object Ref]
var nsString = $.CFMakeCollectable(cfString); // => $("foo")
To make this easier to use in your code, you might define a .toNS() function on the Ref prototype:
Ref.prototype.toNS = function () { return $.CFMakeCollectable(this); }
Here is how you would use this new function with a CFString constant:
ObjC.import('CoreServices')
$.kUTTypeHTML.toNS() // => $("public.html")
$.kUTTypeHTML appears to return a CFDictionary (see below), so you should find useable methods at:
EDIT: It turns out that some typing complexities in JXA-ObjC-CF interactions mean that snippet below is NOT a reliable or generally applicable approach to learning the type of a CF Object reference. (See the discussion that follows).
https://developer.apple.com/library/mac/documentation/CoreFoundation/Reference/CFDictionaryRef/
ObjC.import('CoreServices')
var data = $.CFStringCreateExternalRepresentation(
null,
$.CFCopyTypeIDDescription(
$.CFGetTypeID($.kUTTypeHTML)
),
'UTF-8',
0
); // CFDataRef
cPtr = $.CFDataGetBytePtr(data);
// --> "CFDictionary"
I guess this will be simple for C++/CLI gurus.
I am creating a wrapper which will expose high-performance C++ native classes to C# WinForms application.
Everything went fine with simple known objects and I could wrap also a callback function to delegate. But now I am a bit confused.
The native C++ class has a following method:
int GetProperty(int propId, void* propInOut)
At first I thought I could use void* as IntPtr, but then I found out that I need to access it from C#. So I thought about a wrapper method:
int GetProperty(int propId, Object^ propInOut)
but as I looked through the C++ source, I found out that the method needs to modify the objects. So obviously I need:
int GetProperty(int propId, Object^% propInOut)
Now I cannot pass Objects to native methods so I need to know how to treat them in the wrapper. As the caller should always know what kind of data he/she is passing/receiving, I declared a wrapper:
int GetProperty(int propId, int dataType, Object^% propInOut)
I guess, I can use it to pass reference and value types, for example, an int like this:
Object count = 100; // yeah, I know boxing is bad but this will not be real-time call anyway
myWrapper.GetProperty(Registry.PROP_SMTH, DATA_TYPE_INT, ref count);
I just added a bunch of dataType constants for all the data types I need:
DATA_TYPE_INT, DATA_TYPE_FLOAT, DATA_TYPE_STRING, DATA_TYPE_DESCRIPTOR, DATA_TYPE_BYTE_ARRAY
(DATA_TYPE_DESCRIPTOR is a simple struct with two fields: int Id and wstring Description - this type will be wrapped too, so I guess marshaling will be simple copying data back and forth; all the native strings are Unicode).
Now, the question is - how to implement the wrapper method for all these 5 types?
When I can just cast Object^% to something (is int, float safe to do that?) and pass to native method, when do I need to use pin_ptr and when I need some more complex marshaling to native and back?
int GetProperty(int propId, int dataType, Object^% propInOut)
{
if(dataType == DATA_TYPE_INT)
{
int* marshaledPropInOut = ???
int result = nativeObject->GetProperty(propId, (void*)marshaledPropInOut);
// need to do anything more?
return result;
}
else
if(dataType == DATA_TYPE_FLOAT)
{
float* marshaledPropInOut = ???
int result = nativeObject->GetProperty(propId, (void*)marshaledPropInOut);
// need to do anything more ?
return result;
}
else
if(dataType == DATA_TYPE_STRING)
{
// will pin_ptr be needed or it is enough with the tracking reference in the declaration?
// the pointers won't get stored anywhere in C++ later so I don't need AllocHGlobal
int result = nativeObject->GetProperty(propId, (void*)marshaledPropInOut);
// need to do anything more?
return result;
}
else
if(dataType == DATA_TYPE_BYTE_ARRAY)
{
// need to convert form managed byte[] to native char[] and back;
// user has already allocated byte[] so I can get the size of array somehow
return result;
}
else
if(dataType == DATA_TYPE_DESCRIPTOR)
{
// I guess I'll have to do a dumb copying between native and managed struct,
// the only problem is pinning of the string again before passing to the native
return result;
}
return -1;
}
P.S. Maybe there is a more elegant solution for wrapping this void* method with many possible datatypes?
It doesn't necessarily make sense to equate a C# object to a void*. There isn't any way to marshal arbitrary data. Even with an object, C# still knows what type it is underneath, and for marshaling to take place -- meaning a conversion from the C++ world to C# or vice-versa -- the type of data needs to be known. A void* is just a pointer to memory of a completely unknown type, so how would you convert it to an object, where the type has to be known?
If you have a limited number of types as you describe that could be passed in from the C# world, it is best to make several overloads in your C++/CLI code, each of which took one of those types, and then you can pin the type passed in (if necessary), convert it to a void*, pass that to your C++ function that takes a void*, and then marshal back as appropriate for the type.
You could implement a case statement as you listed, but then what do you do if you can't handle the type that was passed in? The person calling the function from C# has no way to know what types are acceptable and the compiler can't help you figure out that you did something wrong.
Suppose I write the following code:
public ref class Data
{
public:
Data()
{
}
Int32 Age;
Int32 year;
};
public void Test()
{
int age = 30;
Int32 year = 2010;
int* pAge = &age;
int* pYear = &year;
Data^ data = gcnew Data();
int* pDataYear = &data->Year; // pData is interior pointer and the compiler will throw error
}
If you compile the program, the compiler will throw error:
error C2440: 'initializing' : cannot convert from 'cli::interior_ptr' to 'int *'
So I learned the "&data->Year" is a type of interior pointer.
UPDATES: I tried to use "&(data->Year)", same error.
But how about pAge and pYear?
Are they native pointers, interior pointers or pinned pointers??
If I want to use them in the following native function:
void ChangeNumber(int* pNum);
Will it be safe to pass either pAge or pYear?
They (pAge and pYear) are native pointers, and passing them to a native function is safe. Stack variables (locals with automatic storage lifetime) are not subject to being rearranged by the garbage collector, so pinning is not necessary.
Copying managed data to the stack, then passing it to native functions, solves the gc-moving-managed-data-around problem in many cases (of course, don't use it in conjunction with callbacks that expect the original variable to be updated before your wrapper has a chance to copy the value back).
To get a native pointer to managed data, you have to use a pinning pointer. This can be slower than the method of copying the value to the stack, so use it for large values or when you really need the function to operate directly on the same variable (e.g. the variable is used in callbacks or multi-threading).
Something like:
pin_ptr<int> p = &mgd_obj.field;
See also the MSDN documentation