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  • Alternatives to C++ Reference/Pointer Syntax

    - by Jon Purdy
    What languages other than C and C++ have explicit reference and pointer type qualifiers? People seem to be easily confused by the right-to-left reading order of types, where char*& is "a reference to a pointer to a character", or a "character-pointer reference"; do any languages with explicit references make use of a left-to-right reading order, such as &*char/ref ptr char? I'm working on a little language project, and legibility is one of my key concerns. It seems to me that this is one of those questions to which it's easy for a person but hard for a search engine to provide an answer. Thanks in advance!

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  • Passing a pointer to a function that doesn't match the requirements of the formal parameter

    - by Andreas Grech
    int valid (int x, int y) { return x + y; } int invalid (int x) { return x; } int func (int *f (int, int), int x, int y) { //f is a pointer to a function taking 2 ints and returning an int return f(x, y); } int main () { int val = func(valid, 1, 2), inval = func(invalid, 1, 2); // <- 'invalid' does not match the contract printf("Valid: %d\n", val); printf("Invalid: %d\n", inval); /* Output: * Valid: 3 * Invalid: 1 */ } At the line inval = func(invalid, 1, 2);, why am I not getting a compiler error? If func expects a pointer to a function taking 2 ints and I pass a pointer to a function that takes a single int, why isn't the compiler complaining? Also, since this is happening, what happens to the second parameter y in the invalid function?

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  • Alternates to C++ Reference/Pointer Syntax

    - by Jon Purdy
    What languages other than C and C++ have explicit reference and pointer type qualifiers? People seem to be easily confused by the right-to-left reading order of types, where char*& is "a reference to a pointer to a character", or a "character-pointer reference"; do any languages with explicit references make use of a left-to-right reading order, such as &*char/ref ptr char? I'm working on a little language project, and legibility is one of my key concerns. It seems to me that this is one of those questions to which it's easy for a person but hard for a search engine to provide an answer. Thanks in advance!

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  • C++ deleting a pointer

    - by eSKay
    On this page, its written that One reason is that the operand of delete need not be an lvalue. Consider: delete p+1; delete f(x); Here, the implementation of delete does not have a pointer to which it can assign zero. Adding a number to a pointer shifts it forward in memory by those many number of sizeof(*p) units. So, what is the difference between delete p and delete p+1, and why would making the pointer 0 only be a problem with delete p+1?

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  • Size of a class with 'this' pointer

    - by psvaibhav
    The size of a class with no data members is returned as 1 byte, even though there is an implicit 'this' pointer declared. Shouldn't the size returned be 4 bytes(on a 32 bit machine)? I came across articles which indicated that 'this' pointer is not counted for calculating the size of the object. But I am unable to understand the reason for this. Also, if any member function is declared virtual, the size of the class is now returned as 4 bytes. This means that the vptr is counted for calculating the size of the object. Why is the vptr considered and 'this' pointer ignored for calculating the size of object?

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  • Boost Shared Pointer: Simultaneous Read Access Across Multiple Threads

    - by Nikhil
    I have a thread A which allocates memory and assigns it to a shared pointer. Then this thread spawns 3 other threads X, Y and Z and passes a copy of the shared pointer to each. When X, Y and Z go out of scope, the memory is freed. But is there a possibility that 2 threads X, Y go out of scope at the exact same point in time and there is a race condition on reference count so instead of decrementing it by 2, it only gets decremented once. So, now the reference count newer drops to 0, so there is a memory leak. Note that, X, Y and Z are only reading the memory. Not writing or resetting the shared pointer. To cut a long story short, can there be a race condition on the reference count and can that lead to memory leaks?

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  • Call function by pointer and set parametrs in memory block

    - by Ellesmess Glain
    Hi, I've little problem : I'm solving problem with calling function by pointer and passing to it parameters in continuous memory block. My goal is to have function named e.g CallFunc(void * func,void *params, unsigned int param_length); that I'll send function pointer, pointer to function's parameters and eventually parameters length and this calling function will call passed function with it's parameters. I will like write this in C/C++, but if somebody has idea, how this resolve in other language, that supports DLL generation and exportet functions, it will be fine too. Thanks for answers, Ellesmess P.S. I'm sorry about my English, but I'm Czech, thanks :o)

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  • Add 64 bit offset to a pointer

    - by Novox
    In F#, there's the NativePtr module, but it seems to only support 32 bit offsets for its’ add/get/set functions, just like System.IntPtr does. Is there a way to add a 64 bit offset to a native pointer (nativeptr<'a) in F#? Of course I could convert all addresses to 64 bit integers, do normal integer operations and then convert the result again to nativeptr<'a, but this would cost additional add and imul instructions. I really want the AGUs to perform the address calculations. For instance, using unsafe in C# you could do something like void* ptr = Marshal.AllocHGlobal(...).ToPointer(); int64 offset = ...; T* newAddr = (T*)ptr + offset; // T has to be an unmanaged type Well actually you can't, because there is no "unmanaged" constraint for type parameters, but at least you can do general pointer arithmetic in a non-generic way. In F# we finally got the unmanaged constraint; but how do I do the pointer arithmetic?

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  • Objective-C classes, pointers to primitive types, etc.

    - by Toby Wilson
    I'll cut a really long story short and give an example of my problem. Given a class that has a pointer to a primitive type as a property: @interface ClassOne : NSObject { int* aNumber } @property int* aNumber; The class is instantiated, and aNumber is allocated and assigned a value, accordingly: ClassOne* bob = [[ClassOne alloc] init]; bob.aNumber = malloc(sizeof(int)); *bob.aNumber = 5; It is then passed, by reference, to assign the aNumber value of a seperate instance of this type of class, accordingly: ClassOne* fred = [[ClassOne alloc] init]; fred.aNumber = bob.aNumber; Fred's aNumber pointer is then freed, reallocated, and assigned a new value, for example 7. Now, the problem I'm having; Since Fred has been assigned the same pointer that Bob had, I would expect that Bob's aNumber will now have a value of 7. It doesn't, because for some reason it's pointer was freed, but not reassigned (it is still pointing to the same address it was first allocated which is now freed). Fred's pointer, however, has the allocated value 7 in a different memory location. Why is it behaving like this? What am I minsunderstanding? How can I make it work like C++ does?

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  • When does invoking a member function on a null instance result in undefined behavior?

    - by GMan
    This question arose in the comments of a now-deleted answer to this other question. Our question was asked in the comments by STingRaySC as: Where exactly do we invoke UB? Is it calling a member function through an invalid pointer? Or is it calling a member function that accesses member data through an invalid pointer? With the answer deleted I figured we might as well make it it's own question. Consider the following code: #include <iostream> struct foo { void bar(void) { std::cout << "gman was here" << std::endl; } void baz(void) { x = 5; } int x; }; int main(void) { foo* f = 0; f->bar(); // (a) f->baz(); // (b) } We expect (b) to crash, because there is no corresponding member x for the null pointer. In practice, (a) doesn't crash because the this pointer is never used. Because (b) dereferences the this pointer (this->x = 5;), and this is null, the program enters undefined behavior. Does (a) result in undefined behavior? What about if both functions are static?

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  • C++ this as thread parameter, variables unavailable

    - by brecht
    I have three classes: class Rtss_Generator { int mv_transfersize; } class Rtss_GenSine : Rtss_Generator class Rtss_GenSineRpm : Rtss_GenSine Rtss_GenSine creates a thread in his constructer, it is started immediatly and the threadfunction is off-course declared static, waiting for an event to start calculating. the problem: all the variables that are accessed through the gen-pointer are 0, but it does not fail. Also, this-address in the constructer and the gen-pointer-address in the thread are the same, so the pointer is ok. this code is created and compile in visual studio 6.0 service pack 2003 ORIGINAL CODE no thread Rtss_GenSine::getNextData() { //[CALCULATION] //mv_transferSize is accessible and has ALWAYS value 1600 which is ok } NEW CODE Rtss_GenSine::Rtss_GenSine() { createThread(NULL, threadFunction, (LPVOID) this,0,0); } Rtss_GenSine::getNextData() { SetEvent(startCalculating); WaitForSingleObject(stoppedCalculaing, INFINITE); } DWORD Rtss_GenSine::threadFunction(LPVOID pParam) { Rtss_GenSine* gen = (Rtss_GenSine*) pParam; while(runThread) { WaitForSingleObject(startCalculating, INFINITE); ResetEvent(startCalculating) //[CALCULATION] //gen->mv_transferSize ---> it does not fail, but is always zero //all variables accessed via the gen-pointer are 0 setEvent(stoppedCalculaing) } }

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  • Using a Function returning apointer as LValue

    - by Amrish
    Why cant I used a function returning a pointer as a lvalue? For example this one works int* function() { int* x; return x; } int main() { int* x = function(); x = new int(9); } but not this int* function() { int* x; return x; } int main() { int* x; function() = x; } While I can use a pointer variable as a lvalue, why can't I use a function returning a pointer as a lvalue? Also, when the function returns a refernce, instead of a pointer, then it becomes a valid lvalue.

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  • C++: Pointers and scope

    - by oh boy
    int* test( ) { int a = 5; int* b = &a; return b; } Will the result of test be a bad pointer? As far as I know a should be deleted and then b would become a messed up pointer, right? How about more complicated things, not an int pointer but the same with a class with 20 members or so?

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  • Function Pointer

    - by Shaista Naaz
    How is that function pointer better than if-else or switch case? Is it because function pointer helps callback functions and thus promotes asynchronous implementation?

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  • PHP array pointer craziness

    - by JMan
    I'm trying to create a "GetCurrentLevel" method that takes a point value as an input and returns what "Level" that corresponds to. I'm storing the Level = Points mapping in an array, but the array pointer is not moving logically when I use it a foreach loop. I've added echo statements for debugging. Here's my class definition: class Levels extends Model { protected $_map = array ( 'None' => 0, 'Bronze' => 50, 'Silver' => 200, 'Gold' => 500 ); public function __construct() { parent::__construct(); } public function GetCurrentLevel($points) { foreach ($this->_map as $name => $threshold) { echo "Level Name: $name<br/>"; echo "Level Threshold: $threshold<br/>"; echo "Current Level: " . key($this->_map) . "<br/>"; echo "Current Threshold: " . current($this->_map) . "<br/>"; if ($points < $threshold) /* Threshold is now above the points, so need to go back one level */ { $previousThreshold = prev($this->_map); echo "Previous Threshold: $previousThreshold<br/>"; echo "Final Level: " . key($this->_map) . "<br/>"; return key($this->_map); } echo "Go to next level <br/>"; } } And here is what I see when I call GetCurrentLevel(60): Level Name: None Level Threshold: 0 Current Level: Bronze //* Looks like foreach immediately moves the array pointer *// Current Threshold: 50 Go to next level Level Name: Bronze Level Threshold: 50 Current Level: Bronze //* WTF? Why hasn't the array pointer moved? *// Current Threshold: 50 Go to next level Level Name: Silver Level Threshold: 200 Current Level: Bronze //* WTF? Why hasn't the array pointer moved? *// Current Threshold: 50 Previous Threshold: 0 Final Level: None But the "Final Level" should be 'Bronze' since 60 points is above the 50 points needed for a Bronze medal, but below the 200 points needed for a Silver medal. Sorry for the long post. Thanks for your help!

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  • python object to native c++ pointer

    - by Lodle
    Im toying around with the idea to use python as an embedded scripting language for a project im working on and have got most things working. However i cant seem to be able to convert a python extended object back into a native c++ pointer. So this is my class: class CGEGameModeBase { public: virtual void FunctionCall()=0; virtual const char* StringReturn()=0; }; class CGEPYGameMode : public CGEGameModeBase, public boost::python::wrapper<CGEPYGameMode> { public: virtual void FunctionCall() { if (override f = this->get_override("FunctionCall")) f(); } virtual const char* StringReturn() { if (override f = this->get_override("StringReturn")) return f(); return "FAILED TO CALL"; } }; Boost wrapping: BOOST_PYTHON_MODULE(GEGameMode) { class_<CGEGameModeBase, boost::noncopyable>("CGEGameModeBase", no_init); class_<CGEPYGameMode, bases<CGEGameModeBase> >("CGEPYGameMode", no_init) .def("FunctionCall", &CGEPYGameMode::FunctionCall) .def("StringReturn", &CGEPYGameMode::StringReturn); } and the python code: import GEGameMode def Ident(): return "Alpha" def NewGamePlay(): return "NewAlpha" def NewAlpha(): import GEGameMode import GEUtil class Alpha(GEGameMode.CGEPYGameMode): def __init__(self): print "Made new Alpha!" def FunctionCall(self): GEUtil.Msg("This is function test Alpha!") def StringReturn(self): return "This is return test Alpha!" return Alpha() Now i can call the first to functions fine by doing this: const char* ident = extract< const char* >( GetLocalDict()["Ident"]() ); const char* newgameplay = extract< const char* >( GetLocalDict()["NewGamePlay"]() ); printf("Loading Script: %s\n", ident); CGEPYGameMode* m_pGameMode = extract< CGEPYGameMode* >( GetLocalDict()[newgameplay]() ); However when i try and convert the Alpha class back to its base class (last line above) i get an boost error: TypeError: No registered converter was able to extract a C++ pointer to type class CGEPYGameMode from this Python object of type Alpha I have done alot of searching on the net but cant work out how to convert the Alpha object into its base class pointer. I could leave it as an object but rather have it as a pointer so some non python aware code can use it. Any ideas?

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  • question regarding pointer in c language

    - by din
    char *sample = "String Value"; &sample is a pointer to the pointer of "String Value" is the above statement right? If the above statement right, what is the equivalent of &sample if my declaration is char sample[] = "String Value"

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  • Converting a pointer C# type to F#??

    - by Brendon
    Hello all I am just a beginner in programing i wish covert some code from C# to F#, I have encotered this code: "float[] v1=new float[10]" I need to use this pointer to pass to the function: "ComputeBuffer bufV1 = new ComputeBuffer(Context, ComputeMemoryFlags.ReadWrite | ComputeMemoryFlags.UseHostPointer, v1);" If i creat an array in F# like this: "let v1 = [| 1.0..10.0 |]" and call now the funaction like this: "let bufV1 = new ComputeBuffer(Context, ComputeMemoryFlags.ReadWrite ||| ComputeMemoryFlags.UseHostPointer, v1)" Is it an error?? How do i pass a pointer??

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  • How to cast a pointer of memory block to std stream

    - by Shahrooz Kia
    I have programed an application on windows XP and in Visual Studio with c++ language. In that app I used LoadResource() API to load a resource for giving a file in the resource memory. It returned a pointer of memory block and I wanna cast the pointer to the std stream to use for compatibility. Could anyone help me?

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  • Call c++ function pointer from c#

    - by Sam
    Is it possible to call a c(++) static function pointer like this typedef int (*MyCppFunc)(void* SomeObject); from c#? void CallFromCSharp(MyCppFunc funcptr, IntPtr param) { funcptr(param); } I need to be able to callback from c# into some old c++ classes. C++ is managed, but the classes are not ref classes (yet). So far I got no idea how to call a c++ function pointer from c#, is it possible?

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  • C++ class pointer

    - by JHollanti
    I know that you can get a reference to a static method like this: typedef void (*pointer)(); pointer p = &MyClass::MyMethod; But is there a way to get a reference to the class itself?

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  • pointer&dynamic memory

    - by gcc
    how many methods are there taking input by using with pointer and dynamic memory input 3 1 2 n k l 2 1 2 p 4 55 62 * # x x is stop character and first input 3 is for another variable int hakko; only hakko use first input the others will be hold in one pointer and input size not determined

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