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  • Advice on "Invalid Pointer Operation" when using complex records

    - by Xaz
    Env: Delphi 2007 <JustificationI tend to use complex records quite frequently as they offer almost all of the advantages of classes but with much simpler handling.</Justification Anyhoo, one particularly complex record I have just implemented is trashing memory (later leading to an "Invalid Pointer Operation" error). This is an example of the memory trashing code: sSignature := gProfiles.Profile[_stPrimary].Signature.Formatted(True); On the second time i call it i get "Invalid Pointer Operation" It works OK if i call it like this: AProfile := gProfiles.Profile[_stPrimary]; ASignature := AProfile.Signature; sSignature := ASignature.Formatted(True); Background Code: gProfiles: TProfiles; TProfiles = Record private FPrimaryProfileID: Integer; FCachedProfile: TProfile; ... public < much code removed > property Profile[ProfileType: TProfileType]: TProfile Read GetProfile; end; function TProfiles.GetProfile(ProfileType: TProfileType): TProfile; begin case ProfileType of _stPrimary : Result := ProfileByID(FPrimaryProfileID); ... end; end; function TProfiles.ProfileByID(iID: Integer): TProfile; begin <snip> if LoadProfileOfID(iID, FCachedProfile) then begin Result := FCachedProfile; end else ... end; TProfile = Record private ... public ... Signature: TSignature; ... end; TSignature = Record private public PlainTextFormat : string; HTMLFormat : string; // The text to insert into a message when using this profile function Formatted(bHTML: boolean): string; end; function TSignature.Formatted(bHTML: boolean): string; begin if bHTML then result := HTMLFormat else result := PlainTextFormat; < SNIP MUCH CODE > end; OK, so I have a record within a record within a record, which is approaching Inception level confusion and I'm the first to admit is not really a good model. Clearly i am going to have to restructure it. What I would like from you gurus is a better understanding of why it is trashing the memory (something to do with the string object that is created then freed...) so that i can avoid making these kinds of errors in future. Thanks

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  • Implications of trying to double free memory space in C

    - by SidNoob
    Here' my piece of code: #include <stdio.h> #include<stdlib.h> struct student{ char *name; }; int main() { struct student s; s.name = malloc(sizeof(char *)); // I hope this is the right way... printf("Name: "); scanf("%[^\n]", s.name); printf("You Entered: \n\n"); printf("%s\n", s.name); free(s.name); // This will cause my code to break } All I know is that dynamic allocation on the 'heap' needs to be freed. My question is, when I run the program, sometimes the code runs successfully. i.e. ./struct Name: Thisis Myname You Entered: Thisis Myname I tried reading this I've concluded that I'm trying to double-free a piece of memory i.e. I'm trying to free a piece of memory that is already free? (hope I'm correct here. If Yes, what could be the Security Implications of a double-free?) While it fails sometimes as its supposed to: ./struct Name: CrazyFishMotorhead Rider You Entered: CrazyFishMotorhead Rider *** glibc detected *** ./struct: free(): invalid next size (fast): 0x08adb008 *** ======= Backtrace: ========= /lib/tls/i686/cmov/libc.so.6(+0x6b161)[0xb7612161] /lib/tls/i686/cmov/libc.so.6(+0x6c9b8)[0xb76139b8] /lib/tls/i686/cmov/libc.so.6(cfree+0x6d)[0xb7616a9d] ./struct[0x8048533] /lib/tls/i686/cmov/libc.so.6(__libc_start_main+0xe6)[0xb75bdbd6] ./struct[0x8048441] ======= Memory map: ======== 08048000-08049000 r-xp 00000000 08:01 288098 /root/struct 08049000-0804a000 r--p 00000000 08:01 288098 /root/struct 0804a000-0804b000 rw-p 00001000 08:01 288098 /root/struct 08adb000-08afc000 rw-p 00000000 00:00 0 [heap] b7400000-b7421000 rw-p 00000000 00:00 0 b7421000-b7500000 ---p 00000000 00:00 0 b7575000-b7592000 r-xp 00000000 08:01 788956 /lib/libgcc_s.so.1 b7592000-b7593000 r--p 0001c000 08:01 788956 /lib/libgcc_s.so.1 b7593000-b7594000 rw-p 0001d000 08:01 788956 /lib/libgcc_s.so.1 b75a6000-b75a7000 rw-p 00000000 00:00 0 b75a7000-b76fa000 r-xp 00000000 08:01 920678 /lib/tls/i686/cmov/libc-2.11.1.so b76fa000-b76fc000 r--p 00153000 08:01 920678 /lib/tls/i686/cmov/libc-2.11.1.so b76fc000-b76fd000 rw-p 00155000 08:01 920678 /lib/tls/i686/cmov/libc-2.11.1.so b76fd000-b7700000 rw-p 00000000 00:00 0 b7710000-b7714000 rw-p 00000000 00:00 0 b7714000-b7715000 r-xp 00000000 00:00 0 [vdso] b7715000-b7730000 r-xp 00000000 08:01 788898 /lib/ld-2.11.1.so b7730000-b7731000 r--p 0001a000 08:01 788898 /lib/ld-2.11.1.so b7731000-b7732000 rw-p 0001b000 08:01 788898 /lib/ld-2.11.1.so bffd5000-bfff6000 rw-p 00000000 00:00 0 [stack] Aborted So why is it that my code does work sometimes? i.e. the compiler is not able to detect at times that I'm trying to free an already freed memory. Has it got to do something with my stack/heap size?

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  • convert string to double

    - by James123
    I have string value in that I need to convert to double in VB.Net. Conditions are like below string = "12345.00232232" if condition is 3 (2 digits after decimal and comma) display = 12,345.00 if condition is 5 (5 digits after decimal and comma) display = 12,345.00232 If Condition is 7 ( 5 digits after decimal and no comma) display = 12345.00232 How can I do that in VB.Net?

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  • Dangling pointer

    - by viswanathan
    How can the below code result in a dangling pointer. { char *cPointer = malloc ( some constant number ); /* some code */ free ( cPointer ); cPointer = NULL; /* some code */ }

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  • Java Double entry table

    - by Tom
    Hi, Does anyone know a double entry table implementation in java I can download ? I need to do something like this 1 2 3 _______ a| x y z b| h l m c| o a k table.get(a,1) would return x Of course, it should use any Object as key, value, etc Thanks in advance

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  • Why is dereferencing a pointer called dereferencing?

    - by optician
    Why is dereferencing called dereferencing? I'm just learning pointers properly, and I'd like to know why dereferencing is called that. It confused me as it sounds like you are removing a reference, rather than going via the pointer to the destination. Can anyone explain why it is called this? To me something like destination or pointed_to_value would make more sense.

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  • How can I declare a pointer structure?

    - by Y_Y
    This probably is one of the easiest questions ever in C programming language... I have the following code: typedef struct node { int data; struct node * after; struct node * before; }node; struct node head = {10,&head,&head}; Is there a way I can make head to be *head [make it a pointer] and still have the availability to use '{ }' [{10,&head,&head}] to declare an instance of head?

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  • C++ using this pointer in constructors

    - by gilbertc
    In c++, during a class constructor, I started a new thread with 'this' pointer as a parameter which will be used in the thread extensively (say, calling member functions). Is that a bad thing to do? Why and what are the consequences? Thanks, Gil.

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  • double accepts_nested_attributes_for

    - by sfusion
    does anyone know if it is possible to do a double nested form for. so that i could upload images to a set from an article form. e.g. Article has_many :image_sets ImageSet belongs_to :article has_many :images Image belongs_to :image_set

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  • select multiple double side

    - by Mercer
    hello, i want to do a select multiple double side like this : http://www.senamion.com/blog/jmultiselect2side.html (Demo2) but i don't know how i can retrieve my data when i click submit button..?

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  • C++ print value of a pointer

    - by user69514
    I have an array of double pointers, but every time I try do print one of the values the address gets printed. How do I print the actual value? cout << arr[i] ? cout << &arr[i] ? they both print the address Does anyone know?

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  • .htaccess double redirect of a 404 page.

    - by peti
    Hi, my custom 404.php page is located in /includes/404.php. My current .htaccess file does the following redirect: ErrorDocument 404 http://imgpls.localhost/includes/404.php So the url looks like: mysite.com/includes/404.php . Basically I need a double redirect: 1) 404 eror page to mysite.com/404.php (so the url looks nice) 2) mysite.com/404.php to mysite.com/includes/404.php where the file actually is. How can I achieve that? Thanks in advance.

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  • Passing a pointer to a function in objective-c

    - by Chiodo
    Hi, i've a stupid questiona about passing pointer. I've this: @interface MyClass : NSObject myobj* foo; -(void)doSomething:(myobj*)aObj; @end @implementation MyClass -(void)doSomething:(myobj*)aObj { cFuncCall(&aObj); //alloc memory and init the object } -(id)init { //init stuff... [self doSomething:foo]; // foo retun 0x0!!! } @end why foo return nil??? It should be initialized by cFuncCall!

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  • Pass a pointer to a proc as an argument

    - by user146780
    I want to pass a pointer to a procedure in c++. I tried passing this LRESULT(*)(HWND, UINT, WPARAM, LPARAM) prc but it didn't work. How is this done? Thanks HWND OGLFRAME::create(HWND parent, LRESULT(*)(HWND, UINT, WPARAM, LPARAM) prc) { if(framehWnd != NULL) { return framehWnd; ZeroMemory(&rwc,sizeof(rwc)); } } By "it didn't work" I mean it's a syntax error.

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