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  • C++ Function pointers vs Switch

    - by Perfix
    What is faster: Function pointers or switch? The switch statement would have around 30 cases, consisting of enumarated unsigned ints from 0 to 30. I could do the following: class myType { FunctionEnum func; string argv[123]; int someOtherValue; }; // In another file: myType current; // Iterate through a vector containing lots of myTypes // ... for ( i=0; i < myVecSize; i ++ ) switch ( current.func ) { case 1: //... break; // ........ case 30: // blah break; } And go trough the switch with func every time. The good thing about switch would also be that my code is more organized than with 30 functions. Or I could do that (not so sure with that): class myType { myReturnType (*func); string argv[123]; int someOtherValue; }; I'd have 30 different functions then, at the beginning a pointer to one of them is assigned to myType. What is probably faster: Switch statement or function pointer? Calls per second: Around 10 million. I can't just test it out - that would require me to rewrite the whole thing. Currently using switch. I'm building an interpreter which I want to be faster than Python & Ruby - every clock cycle matters!

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  • Problem with passing array of pointers to struct among functions in C

    - by karatemonkey
    The Code that follows segfaults on the call to strncpy and I can't see what I am doing wrong. I need another set of eyes to look it this. Essentially I am trying to alloc memory for a struct that is pointed to by an element in a array of pointers to struct. #include <stdio.h> #include <stdlib.h> #include <string.h> #define MAX_POLICY_NAME_SIZE 64 #define POLICY_FILES_TO_BE_PROCESSED "SPFPolicyFilesReceivedOffline\0" typedef struct TarPolicyPair { int AppearanceTime; char *IndividualFile; char *FullPolicyFile; } PolicyPair; enum { bwlist = 0, fzacts, atksig, rules, MaxNumberFileTypes }; void SPFCreateIndividualPolicyListing(PolicyPair *IndividualPolicyPairtoCreate ) { IndividualPolicyPairtoCreate = (PolicyPair *) malloc(sizeof(PolicyPair)); IndividualPolicyPairtoCreate->IndividualFile = (char *)malloc((MAX_POLICY_NAME_SIZE * sizeof(char))); IndividualPolicyPairtoCreate->FullPolicyFile = (char *)malloc((MAX_POLICY_NAME_SIZE * sizeof(char))); IndividualPolicyPairtoCreate->AppearanceTime = 0; memset(IndividualPolicyPairtoCreate->IndividualFile, '\0', (MAX_POLICY_NAME_SIZE * sizeof(char))); memset(IndividualPolicyPairtoCreate->FullPolicyFile, '\0', (MAX_POLICY_NAME_SIZE * sizeof(char))); } void SPFCreateFullPolicyListing(SPFPolicyPair **CurrentPolicyPair, char *PolicyName, char *PolicyRename) { int i; for(i = 0; i < MaxNumberFileTypes; i++) { CreateIndividualPolicyListing((CurrentPolicyPair[i])); // segfaults on this call strncpy((*CurrentPolicyPair)[i].IndividualFile, POLICY_FILES_TO_BE_PROCESSED, (SPF_POLICY_NAME_SIZE * sizeof(char))); } } int main() { SPFPolicyPair *CurrentPolicyPair[MaxNumberFileTypes] = {NULL, NULL, NULL, NULL}; int i; CreateFullPolicyListing(&CurrentPolicyPair, POLICY_FILES_TO_BE_PROCESSED, POLICY_FILES_TO_BE_PROCESSED); return 0; }

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  • deleting an array that stores pointers to some objects

    - by memC
    hi, I am storing pointers to elements of a vec_A in an array A* a_ptrs[3] . Assume that vec_A will not be resized. So, a_ptrs[i] will point to the correct element. My question is: Suppose A* a_ptrs[3] is declared in a class B. Since it is not created using 'new' I am guessing I don't need to delete it in the destructor. Am I right?? class A { public: int getNumber(); A(int val); ~A(){}; private: int num; }; A::A(int val){ num = val; }; int A::getNumber(){ return num; }; int main(){ int i =0; int num; std::vector<A> vec_A; for ( i = 0; i < 10; i++){ vec_A.push_back(A(i)); } A* a_ptrs[3]; a_ptrs[0] = &vec_A[0]; a_ptrs[1] = &vec_A[3]; a_ptrs[2] = &vec_A[5]; for (i = 0; i<3; i++){ std::cout<<"\n: a_ptrs[i].getNumber() = "<<a_ptrs[i]->getNumber(); } std::cout << "\nPress RETURN to continue..."; std::cin.get(); return 0; }

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  • c++ Multiple Inheritance - Compiler modifying my pointers

    - by Bob
    If I run the following code, I get different addresses printed. Why? class Base1 { int x; }; class Base2 { int y; }; class Derived : public Base1, public Base2 { }; union U { Base2* b; Derived* d; U(Base2* b2) : b(b) {} }; int main() { Derived* d = new Derived; cout << d << "\n"; cout << U(d).d << "\n"; return 0; } Even more fun is if you repeatedly go in and out of the union the address keeps incrementing by 4, like this int main() { Derived* d = new Derived; cout << d << "\n"; d = U(d).d; cout << d << "\n"; d = U(d).d; cout << d << "\n"; return 0; } If the union is modified like this, then the problem goes away union U { void* v; Base2* b; Derived* d; U(void* v) : v(v) {} }; Also, if either base class is made empty, the problem goes away. Is this a compiler bug? I want it to leave my pointers the hell alone.

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  • Pointer arithmetic and arrays: what's really legal?

    - by bitcruncher
    Consider the following statements: int *pFarr, *pVarr; int farr[3] = {11,22,33}; int varr[3] = {7,8,9}; pFarr = &(farr[0]); pVarr = varr; At this stage, both pointers are pointing at the start of each respective array address. For *pFarr, we are presently looking at 11 and for *pVarr, 7. Equally, if I request the contents of each array through *farr and *varr, i also get 11 and 7. So far so good. Now, let's try pFarr++ and pVarr++. Great. We're now looking at 22 and 8, as expected. But now... Trying to move up farr++ and varr++ ... and we get "wrong type of argument to increment". Now, I recognize the difference between an array pointer and a regular pointer, but since their behaviour is similar, why this limitation? This is further confusing to me when I also consider that in the same program I can call the following function in an ostensibly correct way and in another incorrect way, and I get the same behaviour, though in contrast to what happened in the code posted above!? working_on_pointers ( pFarr, farr ); // calling with expected parameters working_on_pointers ( farr, pFarr ); // calling with inverted parameters . void working_on_pointers ( int *pExpect, int aExpect[] ) { printf("%i", *pExpect); // displays the contents of pExpect ok printf("%i", *aExpect); // displays the contents of aExpect ok pExpect++; // no warnings or errors aExpect++; // no warnings or errors printf("%i", *pExpect); // displays the next element or an overflow element (with no errors) printf("%i", *aExpect); // displays the next element or an overflow element (with no errors) } Could someone help me to understand why array pointers and pointers behave in similar ways in some contexts, but different in others? So many thanks. EDIT: Noobs like myself could further benefit from this resource: http://www.panix.com/~elflord/cpp/gotchas/index.shtml

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  • C# double-quoted path name being escaped when read from file

    - by KrisTrip
    I am trying to read in a text input file that contains a list of filenames (one per line). However, I am running into an issue if the user double-quotes the path (because it has a space in it). For example, a normal input file might have: C:\test\test.tiff C:\test\anothertest.tiff C:\test\lasttest.tiff These get read in fine by my code ("C:\\test\\test.tiff" etc) However, if I have the following input file: "C:\test with spaces\test.tiff" "C:\test with spaces\anothertest.tiff" "C:\test with spaces\lasttest.tiff" These get read in double-quotes and all ("\"C:\\test with spaces\\test.tiff\"" etc). This becomes a problem when I try to open the files (I understandably get invalid character exceptions). My question is, how do I fix this? I want to allow users to input quoted strings and handle them correctly. My first impression was to just write a little method that strips off beginning or ending quotes, but I thought there might be a better way.

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  • Double of Total Problem

    - by Gopal
    Table1 ID | WorkTime ----------------- 001 | 10:50:00 001 | 00:00:00 002 | .... WorkTime Datatype is *varchar(. SELECT ID, CONVERT(varchar(10), TotalSeconds1 / 3600) + ':' + RIGHT('00' + CONVERT(varchar(2), (TotalSeconds1 - TotalSeconds1 / 3600 * 3600) / 60), 2) + ':' + RIGHT('00' + CONVERT(varchar(2), TotalSeconds1 - (TotalSeconds1 / 3600 * 3600 + (TotalSeconds1 - TotalSeconds1 / 3600 * 3600) / 60 * 60)), 2) AS TotalWork From ( SELECT ID, SUM(DATEDIFF(second, CONVERT(datetime, '1/1/1900'), CONVERT(datetime, '1/1/1900 ' + WorkTime))) AS TotalSeconds1 FROM table1 group by ID) AS tab1 where id = '001' The above Query is showing "double the total of time" For Example From table1 i want to calculate the total WorkTime, when i run the above query it is showing ID WorkTime 001 21:40:00 002..., But it should show like this ID Worktime 001 10:50:00 ..., How to avoid the double total of worktime. How to modify my query. Need Query Help

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  • How to access pixels of an NSBitmapImageRep?

    - by Paperflyer
    I have an NSBitmapImageRep that is created like this: NSBitmapImageRep *imageRep = [[NSBitmapImageRep alloc] initWithBitmapDataPlanes:NULL pixelsWide:waveformSize.width pixelsHigh:waveformSize.height bitsPerSample:8 samplesPerPixel:4 hasAlpha:YES isPlanar:YES colorSpaceName:NSCalibratedRGBColorSpace bytesPerRow:0 bitsPerPixel:0]; Now I want to access the pixel data so I get a pointer to the pixel planes using unsigned char *bitmapData; [imageRep getBitmapDataPlanes:&bitmapData]; According to the Documentation this returns a C array of five character pointers. But how can it do that? since the type of the argument is unsigned char **, it can only return an array of chars, but not an array of char pointers. So, this leaves me wondering how to access the individual pixels. Do you have an idea how to do that? (I know there is the method – setColor:atX:y:, but it seems to be pretty slow if invoked for every single pixel of a big bitmap.)

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  • Function pointer arrays in Fortran

    - by Eduardo Dobay
    I can create function pointers in Fortran 90, with code like real, external :: f and then use f as an argument to another function/subroutine. But what if I want an array of function pointers? In C I would just do double (*f[])(int); to create an array of functions returning double and taking an integer argument. I tried the most obvious, real, external, dimension(3) :: f but gfortran doesn't let me mix EXTERNAL and DIMENSION. Is there any way to do what I want? (The context for this is a program for solving a system of differential equations, so I could input the equations without having a million parameters in my subroutines.)

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  • Double pointer as Objective-C block parameter

    - by George WS
    Is it possible (and if so, safe) to create/use a block which takes a double pointer as an argument? For instance: - (void)methodWithBlock:(void (^)(NSError **error))block; Additional context, research, and questions: I'm using ARC. When I declare the method above and attempt to call it, XCode autocompletes my method invocation as follows: [self methodWithBlock:^(NSError *__autoreleasing *error) {}]; What does __autoreleasing mean here and why is it being added? I presume it has something to do with ARC. If this is possible and safe, can the pointer still be dereferenced in the block as it would be anywhere else? In general, what are the important differences between doing what I'm describing, and simply passing a double pointer as a method parameter (e.g. - (void)methodWithDoublePointer:(NSError **)error;)? What special considerations, if any, should be taken into account (again assuming this is possible at all)?

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  • Conversion of pointer-to-pointer between derived and base classes?

    - by Mike Mueller
    Regarding the following C++ program: class Base { }; class Child : public Base { }; int main() { // Normal: using child as base is allowed Child *c = new Child(); Base *b = c; // Double pointers: apparently can't use Child** as Base** Child **cc = &c; Base **bb = cc; return 0; } GCC produces the following error on the last assignment statement: error: invalid conversion from ‘Child**’ to ‘Base**’ My question is in two parts: Why is there no implicit conversion from Child** to Base**? I can make this example work with a C-style cast or a reinterpret_cast. Using these casts means throwing away all type safety. Is there anything I can add to the class definitions to make these pointers cast implicitly, or at least phrase the conversion in a way that allows me to use static_cast instead?

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  • Arrow operator (->) usage in C

    - by Mohit Deshpande
    I am currently learning C by reading a good beginner's book called "Teach Yourself C in 21 Days" (I have already learned Java and C# so I am moving at a much faster pace). I was reading the chapter on pointers and the - (arrow) operator came up without explanation. I think that it is used to call members and functions (like the equivalent of the . (dot) operator, but for pointers instead of members). But I am not entirely sure. Could I please get an explanation and a code sample?

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  • .net converting bytearray to double[]

    - by AJ
    Hello, I am working with a database from a legacy app which stores 24 floating point values (doubles) as a byte array of length 192, so 8 bytes per value. This byte array is stored in a column of type image in a SQL Server 2005 database. In my .net app I need to read this byte array and convert it to a array of type Double[24]. I can access the field easy enough reader.GetBytes(...) but how to convert the returned ByteArray to Double[24] Any ideas? Thanks, AJ

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  • Databinding to type double - decimal mark lost

    - by user1277327
    I have a project where I'm databinding a gridview to a list, where one column is databound to a gridview. The problem I have is that with the double being 5.5 on one computer it appears as 5.5 in the gridview. But on another it looks like 55, the decimal mark dissapears. So 3.14 will look like 314 etc. The error occurs with the following code: myDatagrid.ItemsSource = someList; Binding binding = new Binding("DoubleValue"); myColumnInDatagrid.Binding = binding; I've also tried using a very simple valueconverter, that just return the double, and parsed it in ConvertBack. I'm pretty new to WPF so I'm sorry if I've made some obvious mistakes, I just don't understand why it works on one computer but not on the other. Perhaps it should be noted that both of the computers use the same operating system, with the same language settings (afaik at least).

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  • C++ smart pointer for a non-object type?

    - by Brian
    Hi, I'm trying to use smart pointers such as auto_ptr, shared_ptr. However, I don't know how to use it in this situation. CvMemStorage *storage = cvCreateMemStorage(); ... use the pointer ... cvReleaseMemStorage(&storage); I'm not sure, but I think that the storage variable is just a malloc'ed memory, not a C++ class object. Is there a way to use the smart pointers for the storage variable? Thank you.

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  • C# huge size 2-dim arrays

    - by 4eburek
    I need to declare square matrices in C# WinForms with more than 20000 items in a row. I read about 2GB .Net object size limit in 32bit and also the same case in 64bit OS. So as I understood the single answer - is using unsafe code or separate library built withing C++ compiler. The problem for me is worth because ushort[20000,20000] is smaller then 2GB but actually I cannot allocate even 700MB of memory. My limit is 650MB and I don't understand why - I have 32bit WinXP with 3GB of memory. I tried to use Marshal.AllocHGlobal(700<<20) but it throws OutOfMemoryException, GC.GetTotalMemory returns 4.5MB before trying to allocate memory. I found only that many people say use unsafe code but I cannot find example of how to declare 2-dim array in heap (any stack can't keep so huge amount of data) and how to work with it using pointers. Is it pure C++ code inside of unsafe{} brackets? Could you please provide a small example of working with matrices using pointers in unsafe code.

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  • C++ smart pointer for non-object type?

    - by Brian
    Hi, I'm trying to use smart pointers such as auto_ptr, shared_ptr. However, I don't know how to use it in this situation. CvMemStorage *storage = cvCreateMemStorage(); ... use the pointer ... cvReleaseMemStorage(&storage); I'm not sure, but I think that the storage variable is just malloc'ed memory, not object. Is there a way to use the smart pointers for the storage variable? Thank you.

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  • Why implement DB connection pointer object as a reference counting pointer? (C++)

    - by DVK
    At our company one of the core C++ classes (Database connection pointer) is implemented as a reference counting pointer. To be clear, the objects are NOT DB connections themselves, but pointers to a DB connection object. The library is very old, and nobody who designed is around anymore. So far, nether I, nor any C++ experts in the company that I asked have come up with a good reason for why this particular design was chosen. Any ideas? It is introducing some problems (partially due to awful reference pointer implementation used), and I'm trying to understand if this design actually has some deep underlying reasons? The usage pattern these days seems to be that the DB connection pointer object is returned by a DB connection manager class, and it's somewhat unclear whether DB connection pointers were designed to be able to be used independently of DB connection manager.

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  • best way to output a full precision double into a text file

    - by flevine100
    Hi, I need to use an existing text file to store some very precise values. When read back in, the numbers essentially need to be exactly equivalent to the ones that were originally written. Now, a normal person would use a binary file... for a number of reasons, that's not possible in this case. So... do any of you have a good way of encoding a double as a string of characters (aside from increasing the precision). My first thought was to cast the double to a char[] and write out the chars. I don't think that's going to work because some of the characters are not visible, produce sounds, and even terminate strings ('\0'... I'm talkin to you!) Thoughts?

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