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• How I return the size of the pointer that I have allocate with malloc?

  - by drigoSkalWalker

  See this example! int main( int argc, char ** argv ) { int *ptr = malloc(100 * sizeof (int)); printf("sizeof(array) is %d bytes\n", sizeof(ptr)); } The printf function return only 4 bytes! What is wrong? Thanks so much!!!

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• How do you free windows handle pointer in Delphi 7?

  - by xkingpin

  I am using a third party tool that is pointing to images in memory with a windows handle. The tool stats that you are responsible for freeing handle. So how would you free that handle in Delphi 7? The datatype for the handle is LONG

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• How can I declare a pointer with filled information in C++?

  - by chacham15

  typedef struct Pair_s { char *first; char *second; } Pair; Pair pairs[] = { {"foo", "bar"}, //this is fine {"bar", "baz"} }; typedef struct PairOfPairs_s { Pair *first; Pair *second; } PairOfPairs; PairOfPairs pops[] = { {{"foo", "bar"}, {"bar", "baz"}}, //How can i create an equivalent of this NEATLY {&pairs[0], &pairs[1]} //this is not considered neat (imagine trying to read a list of 30 of these) }; How can I achieve the above style declaration semantics?

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• Assigning a pointer variable to a const int in C++?

  - by John

  I'm wondering if anyone can explain the following to me: If I write int i = 0; float* pf = i; I get a compile error (gcc 4.2.1): error: invalid conversion from ‘int’ to ‘float*’ Makes sense - they are obviously two completely different types. But if instead I write const int i = 0; float* pf = i; It compiles without error. Why should the 'const' make a difference on the right hand side of the assignment? Isn't part of the idea of the 'const' keyword to be able to enforce type constraints for constant values? Any explanation I have been able to come up with feels kind of bogus. And none of my explanations also explain the fact that const int i = 1; float* pf = i; fails to compile. Can anyone offer an explanation?

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• Is it possible to get a pointer to String^'s internal array in C++/CLI?

  - by CannibalSmith

  The goal is to avoid copying the string data when I need a const wchar_t*. The answer seems to be yes, but the function PtrToStringChars doesn't have its own MSDN entry (it's only mentioned in the KB and blogs as a trick). That made me suspicious and I want to check with you guys. Is it safe to use that function?

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• Is it standard C++ to set the value of a member pointer to the address of another member in the cons

  - by SilverSun

  Is this valid? class Foo { Bar m_bar; Bar * m_woo; public: Foo() : m_bar(42, 123), m_woo(&m_bar) { } };

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• how to specify a pointer to an overloaded function?

  - by davka

  I want to pass an overloaded function to the std::for_each() algorithm. e.g.: void f(char c); void f(int i); std::string s("example"); std::for_each(s.begin(), s.end(), f); I'd expect the compiler to resolve f() by the iterator type. Apparently, it (gcc 4.1.2) doesn't do it. So, how can I specify which f() I want? thanks a lot

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• What happens when you deallocate a pointer twice or more in C++?

  - by flopex

  int main(){ Employee *e = new Employee(); delete e; delete e; ... delete e; return 0; }

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• Should I pointer-cast from a private derived class to its base class?

  - by skydoor

  I found this from C++FAQ Generally, No. From a member function or friend of a privately derived class, the relationship to the base class is known, and the upward conversion from PrivatelyDer* to Base* (or PrivatelyDer& to Base&) is safe; no cast is needed or recommended. However users of PrivatelyDer should avoid this unsafe conversion, since it is based on a private decision of PrivatelyDer, and is subject to change without notice. How to understand the above words? I don't think the explanation is correct or accurate. I have a code like this class A{ }; class B: private A{ }; int main(){ B *b = new B(); A *a = new A(); a = b; //wrong a = (A*)b; //right }

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• Null pointer to struct which has zero size (empty)... It is a good practice?

  - by ProgramWriter

  Hi2All.. I have some null struct, for example: struct null_type { NullType& someNonVirtualMethod() { return *this; } }; And in some function i need to pass reference to this type. Reason: template <typename T1 = null_type, typename T2 = null_type, ... > class LooksLikeATupleButItsNotATuple { public: LooksLikeATupleButItsNotATuple(T1& ref1 = defParamHere, T2& ref2 = andHere..) : _ref1(ref1), _ref2(ref2), ... { } void someCompositeFunctionHere() { _ref1.someNonVirtualMethod(); _ref2.someNonVirtualMethod(); ... } private: T1& _ref1; T2& _ref2; ...; }; It is a good practice to use null reference as a default parameter?: *static_cast<NullType*>(0) It works on MSVC, but i have some doubts...

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• What is purpose of a this pointer in C++ ?

  - by de costo

  What is purpose of this keyword. Doesn't the methods in a class have access to other peer members in the same class ? WHat is the need to call a this to call peer methods inside a class ??

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• Writting a getter for a pointer to a function .

  - by nomemory

  I have the following problem: "list.c" struct nmlist_element_s { void *data; struct nmlist_element_s *next; }; struct nmlist_s { nmlist_element *head; nmlist_element *tail; unsigned int size; void (*destructor)(void *data); int (*match)(const void *e1, const void *e2); }; /*** Other code ***/ What will be the signature for a function that returns 'destructor' ?

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• Does the pointer get from sqlite3_column_blob() method need to be delete?

  - by quantity

  Like this: const void * test = sqlite3_column_blob(stat, 1); Can I delete or delete[] test?

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• Incorrect data when passing pointer a list of pointers to a function. (C++)

  - by Phil Elm

  I'm writing code for combining data received over multiple sources. When the objects received (I'll call them MyPacket for now), they are stored in a standard list. However, whenever I reference the payload size of a partial MyPacket, the value shows up as 1 instead of the intended size. Here's the function code: MyPacket* CombinePackets(std::list<MyPacket*>* packets, uint8* current_packet){ uint32 total_payload_size = 0; if(packets->size() <= 0) return NULL; //For now. std::list<MyPacket*>::iterator it = packets->begin(); //Some minor code here, not relevant to the problem. for(uint8 index = 0; index < packets->size(); index++){ //(*it)->GetPayloadSize() returns 1 when it should show 1024. I've tried directly accessing the variable and more, but I just can't get it to work. total_payload_size += (*it)->GetPayloadSize(); cout << "Adding to total payload size value: " << (*it)->GetPayloadSize() << endl; std::advance(it,1); } MyPacket* packet = new MyPacket(); //Byte is just a typedef'd unsigned char. packet->payload = (byte) calloc(total_payload_size, sizeof(byte)); packet->payload_size = total_payload_size; it = packets->begin(); //Go back to the beginning again. uint32 big_payload_index = 0; for(uint8 index = 0; index < packets->size(); index++){ if(current_packet != NULL) *current_packet = index; for(uint32 payload_index = 0; payload_index < (*it)->GetPayloadSize(); payload_index++){ packet->payload[big_payload_index] = (*it)->payload[payload_index]; big_payload_index++; } std::advance(it,1); } return packet; } //Calling code std::list<MyPacket*> received = std::list<MyPacket*>(); //The code that fills it is here. std::list<MyPacket*>::iterator it = received.begin(); cout << (*it)->GetPayloadSize() << endl; // Outputs 1024 correctly! MyPacket* final = CombinePackets(&received,NULL); cout << final->GetPayloadSize() << endl; //Outputs 181, which happens to be the number of elements in the received list. So, as you can see above, when I reference (*it)-GetPayloadSize(), it returns 1 instead of the intended 1024. Can anyone see the problem and if so, do you have an idea on how to fix this? I've spent 4 hours searching and trying new solutions, but they all keep returning 1... EDIT:

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• MIPS return address in main

  - by Alexander

  I am confused why in the code below I need to decrement the stack pointer and store the return address again. If I don't do that... then PCSpim keeps on looping.. Why is that? ######################################################################################################################## ### main ######################################################################################################################## .text .globl main main: addi $sp, $sp, -4 # Make space on stack sw $ra, 0($sp) # Save return address # Start test 1 ############################################################ la $a0, asize1 # 1st parameter: address of asize1[0] la $a1, frame1 # 2nd parameter: address of frame1[0] la $a2, window1 # 3rd parameter: address of window1[0] jal vbsme # call function # Printing $v0 add $a0, $v0, $zero # Load $v0 for printing li $v0, 1 # Load the system call numbers syscall # Print newline. la $a0, newline # Load value for printing li $v0, 4 # Load the system call numbers syscall # Printing $v1 add $a0, $v1, $zero # Load $v1 for printing li $v0, 1 # Load the system call numbers syscall # Print newline. la $a0, newline # Load value for printing li $v0, 4 # Load the system call numbers syscall # Print newline. la $a0, newline # Load value for printing li $v0, 4 # Load the system call numbers syscall ############################################################ # End of test 1 lw $ra, 0($sp) # Restore return address addi $sp, $sp, 4 # Restore stack pointer jr $ra # Return ######################################################################################################################## ### vbsme ######################################################################################################################## #.text .globl vbsme vbsme: addi $sp, $sp, -4 # create space on the stack pointer sw $ra, 0($sp) # save return address exit: add $v1, $t5, $zero # (v1) x coordinate of the block in the frame with the minimum SAD add $v0, $t4, $zero # (v0) y coordinate of the block in the frame with the minimum SAD lw $ra, 0($sp) # restore return address addi $sp, $sp, 4 # restore stack pointer jr $ra # return If I delete: addi $sp, $sp, -4 # create space on the stack pointer sw $ra, 0($sp) # save return address and lw $ra, 0($sp) # restore return address addi $sp, $sp, 4 # restore stack pointer on vbsme: PCSpim keeps on running... Why??? I shouldn't have to increment/decrement the stack pointer on vbsme and then do the jr again right? The jal in main is supposed to handle that

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• Is it valid to use unsafe struct * as an opaque type instead of IntPtr in .NET Platform Invoke?

  - by David Jeske

  .NET Platform Invoke advocates declaring pointer types as IntPtr. For example, the following [DllImport("user32.dll")] static extern IntPtr SendMessage(IntPtr hWnd, UInt32 Msg, Int32 wParam, Int32 lParam); However, I find when interfacing with interesting native interfaces, that have many pointer types, flattening everything into IntPtr makes the code very hard to read and removes the typical typechecking that a compiler can do. I've been using a pattern where I declare an unsafe struct to be an opaque pointer type. I can store this pointer type in a managed object, and the compiler can typecheck it form me. For example: class Foo { unsafe struct FOO {}; // opaque type unsafe FOO *my_foo; class if { [DllImport("mydll")] extern static unsafe FOO* get_foo(); [DllImport("mydll")] extern static unsafe void do_something_foo(FOO *foo); } public unsafe Foo() { this.my_foo = if.get_foo(); } public unsafe do_something_foo() { if.do_something_foo(this.my_foo); } While this example may not seem different than using IntPtr, when there are several pointer types moving between managed and native code, using these opaque pointer types for typechecking is a godsend. I have not run into any trouble using this technique in practice. However, I also have not seen an examples of anyone using this technique, and I wonder why. Is there any reason that the above code is invalid in the eyes of the .NET runtime? My main question is about how the .NET GC system treats "unsafe FOO *my_foo". Is this pointer something the GC system is going to try to trace, or is it simply going to ignore it? My hope is that because the underlying type is a struct, and it's declared unsafe, that the GC would ignore it. However, I don't know for sure. Thoughts?

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• How to call different methods from single webservices class

  - by pointer

  I have a following RESTful webservice, I have two methods for http get. One function signs in and other function signs out a user from an application. Following is the code: import javax.ws.rs.core.Context; import javax.ws.rs.core.UriInfo; import javax.ws.rs.PathParam; import javax.ws.rs.Consumes; import javax.ws.rs.PUT; import javax.ws.rs.Path; import javax.ws.rs.GET; import javax.ws.rs.POST; import javax.ws.rs.Produces; import javax.ws.rs.QueryParam; /** * REST Web Service * * @author Pointer */ @Path("generic") public class GenericResource { @Context private UriInfo context; /** * Creates a new instance of GenericResource */ public GenericResource() { } /** * Retrieves representation of an instance of * com.ef.apps.xmpp.ws.GenericResource * * @return an instance of java.lang.String */ @GET @Produces("text/html") public String SignIn(@QueryParam("username") String username, @QueryParam("password") String password, @QueryParam("extension") String extension) { //TODO return proper representation object return "Credentials " + username + " : " + password + " : " + extension; } @GET @Produces("text/html") public String SignOut(@QueryParam("username") String username, @QueryParam("password") String password, @QueryParam("extension") String extension) { //TODO return proper representation object return "Credentials " + username + " : " + password + " : " + extension; } } Now, where would I specify that which function I want to call for http get?

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• Should we use p(..) or (*p)(..) when p is a function pointer?

  - by q0987

  Reference: [33.11] Can I convert a pointer-to-function to a void*? #include "stdafx.h" #include <iostream> int f(char x, int y) { return x; } int g(char x, int y) { return y; } typedef int(*FunctPtr)(char,int); int callit(FunctPtr p, char x, int y) // original { return p(x, y); } int callitB(FunctPtr p, char x, int y) // updated { return (*p)(x, y); } int _tmain(int argc, _TCHAR* argv[]) { FunctPtr p = g; // original std::cout << p('c', 'a') << std::endl; FunctPtr pB = &g; // updated std::cout << (*pB)('c', 'a') << std::endl; return 0; } Question Which way, the original or updated, is the recommended method? Thank you Although I do see the following usage in the original post: void baz() { FredMemFn p = &Fred::f; ? declare a member-function pointer ... }

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• jQuery and Firebug

  - by Jeffrey Karbowski

  I am using jQuery's cycle plugin, and found that I can call up the default for "speed" by typing this into Firebug's console: $.fn.cycle.defaults.speed 1000 I would like to know how to call up the override I have for speed: $('.xxx').cycle({ speed: 1700 }); If you have the answer, please let me know the steps taken to figure it out so I can understand Firebug better. Thanks a bunch!

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• Esoteric C++ operators

  - by Neil G

  What is the purpose of the following esoteric C++ operators? Pointer to member ::* Bind pointer to member by pointer ->* Bind pointer to member by reference .* (reference)

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• Any way in C++ to forward declare a function prototype?

  - by jsyjr

  I make regular use of forward class declarations and pointers to such classes. I now have a need to pass a function pointer through a number of layers. I would prefer to include the header that declares my function pointer's prototype only into the module that dereferences a function pointer rather than into each layer that simply passes along that pointer value. Is this possible?

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• Use jQuery to alter css for "html" and "*"

  - by Chris

  Apologies if this is incredibly easy but I want to be able to do the following in jQuery. Current CSS * { cursor: url('/web/resources/graphics/blank.cur'), pointer; } html { cursor: url('/web/resources/graphics/blank.cur'), pointer; } Desired CSS change (through jQuery only) * { cursor: url('/web/resources/graphics/blankDot.cur'), pointer; } html { cursor: url('/web/resources/graphics/blankDot.cur'), pointer; }

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• USB Flash not recognised by Windows and BIOS, but works fine in Linux

  - by bbalegere

  I have a Transcend JetFLash 2GB USB Drive.It was working fine and I had been using it occasionally. All of sudden it stopped working in all versions of Windows . The USB Drive is also not recognised by the BIOS.It does not show in the list of bootable devices.(It used show up in the list earlier) However the USB Drive works fine in my Linux Mint 11 OS. Running dmesg gives this [ 941.812192] usb 1-2: new high speed USB device using ehci_hcd and address 4 [ 941.936178] usb 1-2: device descriptor read/64, error -71 [ 942.164188] usb 1-2: device descriptor read/64, error -71 [ 942.380189] usb 1-2: new high speed USB device using ehci_hcd and address 5 [ 942.504138] usb 1-2: device descriptor read/64, error -71 [ 942.732179] usb 1-2: device descriptor read/64, error -71 [ 942.948154] usb 1-2: new high speed USB device using ehci_hcd and address 6 [ 943.364134] usb 1-2: device not accepting address 6, error -71 [ 943.476172] usb 1-2: new high speed USB device using ehci_hcd and address 7 [ 943.892140] usb 1-2: device not accepting address 7, error -71 [ 943.892191] hub 1-0:1.0: unable to enumerate USB device on port 2 [ 944.296190] usb 2-2: new full speed USB device using uhci_hcd and address 3 [ 944.438251] usb 2-2: not running at top speed; connect to a high speed hub [ 944.709928] usbcore: registered new interface driver uas [ 944.729999] Initializing USB Mass Storage driver... [ 944.730509] scsi6 : usb-storage 2-2:1.0 [ 944.730908] usbcore: registered new interface driver usb-storage [ 944.730917] USB Mass Storage support registered. [ 945.736320] scsi 6:0:0:0: Direct-Access JetFlash Transcend 2GB 8.07 PQ: 0 ANSI: 2 [ 945.744547] sd 6:0:0:0: Attached scsi generic sg1 type 0 [ 945.753316] sd 6:0:0:0: [sdb] 3944448 512-byte logical blocks: (2.01 GB/1.88 GiB) [ 945.758274] sd 6:0:0:0: [sdb] Write Protect is off [ 945.758288] sd 6:0:0:0: [sdb] Mode Sense: 03 00 00 00 [ 945.765167] sd 6:0:0:0: [sdb] No Caching mode page present [ 945.765181] sd 6:0:0:0: [sdb] Assuming drive cache: write through [ 945.784309] sd 6:0:0:0: [sdb] No Caching mode page present [ 945.784323] sd 6:0:0:0: [sdb] Assuming drive cache: write through [ 946.239512] sdb: sdb1 [ 946.257279] sd 6:0:0:0: [sdb] No Caching mode page present [ 946.257292] sd 6:0:0:0: [sdb] Assuming drive cache: write through [ 946.257302] sd 6:0:0:0: [sdb] Attached SCSI removable disk Looks like there is something wrong the USB Drive.It is not recognised in any computer running Windows. Is there any way to fix this? Any idea why this problem occurred ?

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• Python: speed up removal of every n-th element from list.

  - by ChristopheD

  I'm trying to solve this programming riddle and althought the solution (see code below) works correct, it is too slow for succesful submission. Any pointers as how to make this run faster? (removal of every n-th element from a list)? Or suggestions for a better algorithm to calculate the same; seems I can't think of anything else then brute-force for now... Basically the task at hand is: GIVEN: L = [2,3,4,5,6,7,8,9,10,11,........] 1. Take the first remaining item in list L (in the general case 'n'). Move it to the 'lucky number list'. Then drop every 'n-th' item from the list. 2. Repeat 1 TASK: Calculate the n-th number from the 'lucky number list' ( 1 <= n <= 3000) My current code (it calculates the 3000 first lucky numbers in about a second on my machine - but unfortunately too slow): """ SPOJ Problem Set (classical) 1798. Assistance Required URL: http://www.spoj.pl/problems/ASSIST/ """ sieve = range(3, 33900, 2) luckynumbers = [2] while True: wanted_n = input() if wanted_n == 0: break while len(luckynumbers) < wanted_n: item = sieve[0] luckynumbers.append(item) items_to_delete = set(sieve[::item]) sieve = filter(lambda x: x not in items_to_delete, sieve) print luckynumbers[wanted_n-1]

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• Mutli-core Processors: Does each "core" run at the full clock speed or some fraction of the full clo

  - by GregH

  Let's say you have a single (1) Intel/AMD x86-64 bit 2 GHz 8 core processor. Does each of the 8 cores all run at the full 2 GHz or, does each core run at some fraction of the full 2 GHz clock (e.g. 250 MHz)?

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