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• Performance of Managed C++ Vs UnManaged/native C++

  - by bsobaid

  I am writing a very high performance application that handles and processes hundreds of events every millisecond. Is Unmanaged C++ faster than managed c++? and why? Managed C++ deals with CLR instead of OS and CLR takes care of memory management, which simplifies the code and is probably also more efficient than code written by "a programmer" in unmanaged C++? or there is some other reason? When using managed, how can one then avoid dynamic memory allocation, which causes a performance hit, if it is all transparent to the programmer and handled by CLR? So coming back to my question, Is managed C++ more efficient in terms of speed than unmanaged C++ and why?

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• Anyone Know a Great Sparse One Dimensional Array Library in Python?

  - by TheJacobTaylor

  I am working on an algorithm in Python that uses arrays heavily. The arrays are typically sparse and are read from and written to constantly. I am currently using relatively large native arrays and the performance is good but the memory usage is high (as expected). I would like to be able to have the array implementation not waste space for values that are not used and allow an index offset other than zero. As an example, if my numbers start at 1,000,000 I would like to be able to index my array starting at 1,000,000 and not be required to waste memory with a million unused values. Array reads and writes needs to be fast. Expanding into new territory can be a small delay but reads and writes should be O(1) if possible. Does anybody know of a library that can do it? Thanks!

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• Resolving Assemblies, the fuzzy way

  - by David Rutten

  Here's the setup: A pure DotNET class library is loaded by an unmanaged desktop application. The Class Library acts as a plugin. This plugin loads little baby plugins of its own (all DotNET Class Libraries), and it does so by reading the dll into memory as a byte-stream, then Assembly asm = Assembly.Load(COFF_Image); The problem arises when those little baby plugins have references to other dlls. Since they are loaded via the memory rather than directly from the disk, the framework often cannot find these referenced assemblies and is thus incapable of loading them. I can add an AssemblyResolver handler to my project and I can see these referenced assemblies drop past. I have a reasonably good idea about where to find these referenced assemblies on the disk, but how can I make sure that the Assmebly I load is the correct one? In short, how do I reliably go from the System.ResolveEventArgs.Name field to a dll file path, presuming I have a list of all the folders where this dll could be hiding)?

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• How to return a string literal from a function

  - by skydoor

  Hi I am always confused about return a string literal or a string from a function. I was told that there might be memory leak because you don't know when the memory will be deleted? For example, in the code below, how to implement foo() so that make the output of the code is "Hello World"? void foo ( ) // you can add parameters here. { } int main () { char *c; foo ( ); printf ("%s",c); return 0; } Also if the return type of foo() is not void, but you can return char*, what should it be.

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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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• What wording in the C++ standard allows static_cast<non-void-type*>(malloc(N)); to work?

  - by ben

  As far as I understand the wording in 5.2.9 Static cast, the only time the result of a void*-to-object-pointer conversion is allowed is when the void* was a result of the inverse conversion in the first place. Throughout the standard there is a bunch of references to the representation of a pointer, and the representation of a void pointer being the same as that of a char pointer, and so on, but it never seems to explicitly say that casting an arbitrary void pointer yields a pointer to the same location in memory, with a different type, much like type-punning is undefined where not punning back to an object's actual type. So while malloc clearly returns the address of suitable memory and so on, there does not seem to be any way to actually make use of it, portably, as far as I have seen.

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• How can I detect endianness on a system where all primitive integer sizes are the same?

  - by Joe Wreschnig

  (This question came out of explaining the details of CHAR_BIT, sizeof, and endianness to someone yesterday. It's entirely hypothetical.) Let's say I'm on a platform where CHAR_BIT is 32, so sizeof(char) == sizeof(short) == sizeof(int) == sizeof(long). I believe this is still a standards-conformant environment. The usual way to detect endianness at runtime (because there is no reliable way to do it at compile time) is to make a union { int i, char c[sizeof(int)] } x; x.i = 1 and see whether x.c[0] or x.c[sizeof(int)-1] got set. But that doesn't work on this platform, as I end up with a char[1]. Is there a way to detect whether such a platform is big-endian or little-endian, at runtime? Obviously it doesn't matter inside this hypothetical system, but one can imagine it is writing to a file, or some kind of memory-mapped area, which another machine reads and reconstructs it according to its (saner) memory model.

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• Core Data data type for just the date - not including time

  - by Jason

  I am new at Core Data, and it seems like it is a great way to manage the data store. However I am also very memory-conscious due to the fact that the iPhone doesn't have that much of it. I was a little surprised to see that the data types are so limited - eg. there is a Date type which includes also the time, but no Date type for just the date! All the time information takes up precious bytes of memory, if I just wanted an attribute with the date (e.g. 2/15/2010 rather than 2/15/2010 02:34:48), how could I do this? Is it possible?

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• hidden forms and thr handles

  - by shraddha

  i am hiding the form using SetVisibleCore to false, but now i cant get the handle of this form in other application which i am retrieving using EnumWindow its giving me exception "Attempted to read or write protected memory. This is often an indication that other memory is corrupt." an ACCESS VIOLATION EXCEPTION. so i am searching on 2 ways 1. find out the other way to get handle here we cant use FindWindow cause its not returning any handle 2. find a another way to hide the form but this should be done before loading of the form so,,,plz help me if anybody can

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• How to write a datatable to excel work book at client side

  - by senthilkumar

  Hi Guys Currently i am doing one project in that we need to generate report from database. Since my server memory is too low im getting 'Out of Memory' Exception when im writing it at serverside and also when i write directly to a excel file using http header as excel file im not able to create multiple sheets since my database table is huge more than 65536 rows. I saw many solution using a third party tool but i cant use those into mine..If anyone already worked on this please give me some direction. Also i tried using javascript but for that i need to use datagrid at server side?? but in my project i m not allowed to use like this.

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• Maximum executable size on the iPhone?

  - by Sirp

  Is there a maximum size of executables or executables + shared objects on the iPhone? I've been developing an app that has been crashing on startup or early in execution with SIGSYS. Removing code from the program has helped, though structuring data so the code is simply not executed does not. This could be memory corruption, of some kind, however when I compiled with -Os rather than -O2 or -O3 the size of my executable goes down from 5.15MB to 3.60MB and the application runs perfectly. I also have a bunch of libraries I use, of course. I'm wondering, is there a limit on the size of executable code on the iPhone? Or am I just 'getting lucky' and masking memory corruption when I use -Os?

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• Using the windows api and C++, how could I load an exe from the hard drive and run it in its own thread?

  - by returneax

  For the sake of learning I'm trying to do what the OS does when launching a program ie. parsing a PE file and giving it a thread of execution. If I have two exe's one called foo.exe and the other bar.exe, how could I have foo.exe load the contents of bar.exe into memory then have it execute from there in its own thread? I know how to get it into memory using MapViewOfFile or by simple loading the contents on the hard drive into a buffer. I'm assuming simply copying the contents of bar.exe on disk into its own suspended thread and running it wouldn't work. I am semi-familiar with PE file internals. All help is very much appreciated, of course :)

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• Deciphering a queer compiler warning about unsigned decimal constant

  - by Artagnon

  This large application has a memory pool library which uses a treap internally to store nodes of memory. The treap is implemented using cpp macros, and the complete file trp.h can be found here. I get the following compiler warning when I attempt to compile the application: warning: this decimal constant is unsigned only in ISO C90 By deleting portions of the macro code and using trial-and-error, I finally found the culprit: #define trp_prio_get(a_type, a_field, a_node) \ (2654435761*(uint32_t)(uintptr_t)(a_node)) I'm not sure what that strange number is doing there, but I assume it's there for a good reason, so I just want to leave it alone. I do want to fix the warning though- any idea why the compiler's saying that it's unsigned only in ISO C90? EDIT: I'm using gcc-4.1

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• Type Declaration - Pointer Asterisk Position

  - by sahs

  Hello, in C++, the following means "allocate memory for an int pointer": int* number; So, the asterisk is part of the variable type; without it, that would mean something else (that's why I usually don't separate the asterisk from the variable type). Then what is the reason the asterisk is considered something else, instead of being part of the type? For example, it seems better, if the following meant "allocate memory for two int pointers": int* number1, number2; Am I wrong?

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• data structure for counting frequencies in a database table-like format

  - by user373312

  i was wondering if there is a data structure optimized to count frequencies against data that is stored in a database table-like format. for example, the data comes in a (comma) delimited format below. col1, col2, col3 x, a, green x, b, blue ... y, c, green now i simply want to count the frequency of col1=x or col1=x and col2=green. i have been storing the data in a database table, but in my profiling and from empirical observation, database connection is the bottle-neck. i have tried using in-memory database solutions too, and that works quite well; the only problem is memory requirements and quirky init/destroy calls. also, i work mainly with java, but have experience with .net, and was wondering if there was any api to work with "tabular" data in a linq way using java. any help is appreciated.

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• MySQL resource usage

  - by Sanjay

  I'm using MySQL with PHP. I want to measure how much memory and other resources MySQL is using when I run a particular query

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• c++ std::ostringstream vs std::string::append

  - by NickSoft

  In all examples that use some kind of buffering I see they use stream instead of string. How is std::ostringstream and << operator different than using string.append. Which one is faster and which one uses less resourses (memory). One difference I know is that you can output different types into output stream (like integer) rather than the limited types that string::append accepts. Here is an example: std::ostringstream os; os << "Content-Type: " << contentType << ";charset=" << charset << "\r\n"; std::string header = os.str(); vs std::string header("Content-Type: "); header.append(contentType); header.append(";charset="); header.append(charset); header.append("\r\n"); Obviously using stream is shorter, but I think append returns reference to the string so it can be written like this: std::string header("Content-Type: "); header.append(contentType) .append(";charset=") .append(charset) .append("\r\n"); And with output stream you can do: std::string content; ... os << "Content-Length: " << content.length() << "\r\n"; But what about memory usage and speed? Especially when used in a big loop. Update: To be more clear the question is: Which one should I use and why? Is there situations when one is preferred or the other? For performance and memory ... well I think benchmark is the only way since every implementation could be different. Update 2: Well I don't get clear idea what should I use from the answers which means that any of them will do the job, plus vector. Cubbi did nice benchmark with the addition of Dietmar Kühl that the biggest difference is construction of those objects. If you are looking for an answer you should check that too. I'll wait a bit more for other answers (look previous update) and if I don't get one I think I'll accept Tolga's answer because his suggestion to use vector is already done before which means vector should be less resource hungry.

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• java servlet: generate zip file from BLOBs

  - by Zack

  I'm trying to zip a large number of pdf files (stored as BLOBs in the DB) and then return the zip as an attachment to the user. What's the best way to do this without running into memory issues? Another note: I actually need to merge some PDFs prior to adding them to the ZipOutputStream. Therefore, a couple PDFs will need to be stored in memory at a time. I assume it would be best to then store them as temporary files on the server before zipping them all?

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• What is faster: multiple `send`s or using buffering?

  - by dauerbaustelle

  I'm playing around with sockets in C/Python and I wonder what is the most efficient way to send headers from a Python dictionary to the client socket. My ideas: use a send call for every header. Pros: No memory allocation needed. Cons: many send calls -- probably error prone; error management should be rather complicated use a buffer. Pros: one send call, error checking a lot easier. Cons: Need a buffer :-) malloc/realloc should be rather slow and using a (too) big buffer to avoid realloc calls wastes memory. Any tips for me? Thanks :-)

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• What is the effect on record size of reordering columns in PostgreSQL?

  - by Summer

  Since Postgres can only add columns at the end of tables, I end up re-ordering by adding new columns at the end of the table, setting them equal to existing columns, and then dropping the original columns. So, what does PostgreSQL do with the memory that's freed by dropped columns? Does it automatically re-use the memory, so a single record consumes the same amount of space as it did before? But that would require a re-write of the whole table, so to avoid that, does it just keep a bunch of blank space around in each record? Thanks! ~S

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• C++ conditional compilation

  - by Shaown

  I have the following code snippet #ifdef DO_LOG #define log(p) record(p) #else #define log(p) #endif void record(char *data){ ..... ..... } Now if I call log("hello world") in my code and DO_LOG isn't defined, will the line be compiled, in other words will it eat up the memory for the string "hello world"? P.S. There are a lot of record calls in the program and it is memory sensitive, so is there any other way to conditionally compile so that it only depends on the #define DO_LOG? Thanks in advance.

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• In a virtual machine monitor such as VMware's ESXi Server, how are shadow page tables implemented?

  - by ali01

  My understanding is that VMMs such as VMware's ESXi Server maintain shadow page tables to map virtual page addresses of guest operating systems directly to machine (hardware) addresses. I've been told that shadow page tables are then used directly by the processor's paging hardware to allow memory access in the VM to execute without translation overhead. I would like to understand a bit more about how the shadow page table mechanism works in a VMM. Is my high level understanding above correct? What kind of data structures are used in the implementation of shadow page tables? What is the flow of control from the guest operating system all the way to the hardware? How are memory access translations made for a guest operating system before its shadow page table is populated? How is page sharing supported? Short of straight up reading the source code of an open source VMM, what resources can I look into to learn more about hardware virtualization?

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• Can my app arrange a gdb breakpoint or watch?

  - by Larry Gritz

  Is there a way for my code to be instrumented to insert a break point or watch on a memory location that will be honored by gdb? (And presumably have no effect when gdb is not attached.) I know how to do such things as gdb commands within the gdb session, but for certain types of debugging it would be really handy to do it "programmatically", if you know what I mean -- for example, the bug only happens with a particular circumstance, not any of the first 11,024 times the crashing routine is called, or the first 43,028,503 times that memory location is modified, so setting a simple break point on the routine or watch point on the variable is not helpful -- it's all false positives. I'm concerned mostly about Linux, but curious about if similar solutions exist for OS X (or Windows, though obviously not with gdb).

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• Multimap Space Issue: Guava

  - by Arpssss

  In my Java code, I am using Guavas Multimap (com.google.common.collect.Multimap) by using this: Multimap< Integer, Integer Index = HashMultimap.create() Here, Multimap key is some portion of URL and value is another portion of URL (converted into integer). Now, I assign my JVM 2560 Mb (2.5 GB) heap space (by using Xmx and Xms). However, it can only store 9 millions of such (key,value) pairs of integers (approx 10 million). But, theoretically (according to memory occupied by int) it should store more. Can anybody help me, 1) Why is this happening (means Multimap is taking lots of space) ? I checked my code with out inserting pairs in Multimap, it takes only 1/2 MB space. 2) Is there any other way or home-baked solution to solve this space issue ? More clearly, how to solve this memory issue ? Thanks in advance and any idea is perfectly OK for me.

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• C++'s std::string pools, debug builds? std::string and valgrind problems

  - by Den.Jekk

  Hello, I have a problem with many valgrind warnings about possible memory leaks in std::string, like this one: 120 bytes in 4 blocks are possibly lost in loss record 4,192 of 4,687 at 0x4A06819: operator new(unsigned long) (vg_replace_malloc.c:230) by 0x383B89B8B0: std::string::_Rep::_S_create(unsigned long, unsigned long, std::allocator<char> const&) (in /usr/lib64/libstdc++.so.6.0.8) by 0x383B89C3B4: (within /usr/lib64/libstdc++.so.6.0.8) by 0x383B89C4A9: std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string(char const*, unsigned long, std::allocator<char> const&) (in /usr/lib64/libstdc++.so.6.0.8) I'm wondering: does std::string (GCC 4.1.2) use any memory pools? if so, is there any way to disable the pools (in form of a debug build etc.)? Regards, Den

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