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  • How to load/save C++ class instance (using STL containers) to disk

    - by supert
    I have a C++ class representing a hierarchically organised data tree which is very large (~Gb, basically as large as I can get away with in memory). It uses an STL list to store information at each node plus iterators to other nodes. Each node has only one parent, but 0-10 children. Abstracted, it looks something like: struct node { public: node_list_iterator parent; // iterator to a single parent node double node_data_array[X]; map<int,node_list_iterator> children; // iterators to child nodes }; class strategy { private: list<node> tree; // hierarchically linked list of nodes struct some_other_data; public: void build(); // build the tree void save(); // save the tree from disk void load(); // load the tree from disk void use(); // use the tree }; I would like to implement the load() and save() to disk, and it should be fairly fast, however the obvious problems are: I don't know the size in advance; The data contains iterators, which are volatile; My ignorance of C++ is prodigious. Could anyone suggest a pure C++ solution please?

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  • Is it possible to open a pipe-based filehandle which prints to a variable in perl?

    - by blackkettle
    Hi, I know I can do this, ------ open(F,"",\$var); print F "something cool"; close(F); print $var; ------ or this, open(F, "| ./prog1 | ./prog2 tmp.file"); print F "something cool"; close(F); but is it possible to combine these? The semantics of what I'd like to do should be clear from the following, open(F,"|./prog1 | ./prog2", \$var); print F "something cool"; close(F); print $var; however the above clearly won't work. A few minutes of experimenting and googling seems to indicate that this is not possible, but I'd like to know if I'm stuck with using the `` to capture the output.

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  • download large files using servlet

    - by niks
    I am using Apache Tomcat Server 6 and Java 1.6 and am trying to write large mp3 files to the ServletOutputStream for a user to download. Files are ranging from a 50-750MB at the moment. The smaller files aren't causing too much of a problem but with the larger files it and getting socket exception broken pipe. File fileMp3 = new File(objDownloadSong.getStrSongFolder() + "/" + strSongIdName); FileInputStream fis = new FileInputStream(fileMp3); response.setContentType("audio/mpeg"); response.setHeader("Content-Disposition", "attachment; filename=\"" + strSongName + ".mp3\";"); response.setContentLength((int) fileMp3.length()); OutputStream os = response.getOutputStream(); try { int byteRead = 0; while ((byteRead = fis.read()) != -1) { os.write(byteRead); } os.flush(); } catch (Exception excp) { downloadComplete = "-1"; excp.printStackTrace(); } finally { os.close(); fis.close(); }

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  • How to copy files without slowing down my app?

    - by Kevin Gebhardt
    I have a bunch of little files in my assets which need to be copied to the SD-card on the first start of my App. The copy code i got from here placed in an IntentService works like a charm. However, when I start to copy many litte files, the whole app gets increddible slow (I'm not really sure why by the way), which is a really bad experience for the user on first start. As I realised other apps running normal in that time, I tried to start a child process for the service, which didn't work, as I can't acess my assets from another process as far as I understood. Has anybody out there an idea how a) to copy the files without blocking my app b) to get through to my assets from a private process (process=":myOtherProcess" in Manifest) or c) solve the problem in a complete different way Edit: To make this clearer: The copying allready takes place in a seperate thread (started automaticaly by IntentService). The problem is not to separate the task of copying but that the copying in a dedicated thread somehow affects the rest of the app (e.g. blocking to many app-specific resources?) but not other apps (so it's not blocking the whole CPU or someting) Edit2: Problem solved, it turns out, there wasn't really a problem. See my answer below.

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  • Memory mapping of files and system cache behavior in WinXP

    - by Canopus
    Our application is memory intensive and deals with reading a large number of disk files. The total load can be more than 3 GB. There is a custom memory manager that uses memory mapped files to achieve reading of such a huge data. The files are mapped into the process memory space only when needed and with this the process memory is well under control. But what is observed is, with memory mapping, the system cache keeps on increasing until it occupies the available physical memory. This leads to the slowing down of the entire system. My question is how to prevent system cache from hogging the physical memory? I attempted to remove the file buffering (by using FILE_FLAG_NO_BUFFERING ), but with this, the read operations take considerable amount of time and slows down the application performance. How to achieve the scalability without sacrificing much on performance. What are the common techniques used in such cases? I dont have a good understanding of the WinXP OS caching behavior. Any good links explaining the same would also be helpful.

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  • Is MS Access still the most efficient RAD tool for small-scale custom apps?

    - by FastAl
    Of the many other development tools I've used, nothing holds a candle to the 'Functionality to Development Effort' ratio of MS Access. The reason I am asking is that I have been out of the language selection process for a few years, working on a large .Net system, and am only anecdotally familiar with the latest development tools outside the .Net world. I'm well aware of the limitations of Access, but for a limited concurrency (usually only 1 user at a time), small business, custom app, has anybody found a comparable end-to-end solution or combination that comes close? It doesn't have to be free, open source, or even Windows based. It just has to allow the same speed of development and maintenance, and maybe even provide some additional amenities like seamless autointegration with a server-based DB Engine (like Access does with its own 'Jet' dbms), better web support, and a file format more compatible with source control. I don't want to miss out on anything. Please share your development experience with your suggestions. Thanks.

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  • Improving File Read Performance (single file, C++, Windows)

    - by david
    I have large (hundreds of MB or more) files that I need to read blocks from using C++ on Windows. Currently the relevant functions are: errorType LargeFile::read( void* data_out, __int64 start_position, __int64 size_bytes ) const { if( !m_open ) { // return error } else { seekPosition( start_position ); DWORD bytes_read; BOOL result = ReadFile( m_file, data_out, DWORD( size_bytes ), &bytes_read, NULL ); if( size_bytes != bytes_read || result != TRUE ) { // return error } } // return no error } void LargeFile::seekPosition( __int64 position ) const { LARGE_INTEGER target; target.QuadPart = LONGLONG( position ); SetFilePointerEx( m_file, target, NULL, FILE_BEGIN ); } The performance of the above does not seem to be very good. Reads are on 4K blocks of the file. Some reads are coherent, most are not. A couple questions: Is there a good way to profile the reads? What things might improve the performance? For example, would sector-aligning the data be useful? I'm relatively new to file i/o optimization, so suggestions or pointers to articles/tutorials would be helpful.

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  • How to get proper alignment when printing to file

    - by user1067334
    I have this Structure the elements of which that I need to write in a text file struct Stage3ADisplay { int nSlot; char *Item; char *Type; int nIndex; unsigned char attributesMD[17]; //the last character is \0 unsigned char contentsMD[17]; //only for regular files - //the last character is \0 }; buffer = malloc(sizeof(Stage3ADisplayVar[nIterator]->nSlot) + sizeof(Stage3ADisplayVar[nIterator]->Item) + sizeof(Stage3ADisplayVar[nIterator]->Type) + sizeof(Stage3ADisplayVar[nIterator]->nIndex) + sizeof(Stage3ADisplayVar[nIterator]->attributesMD) + sizeof(Stage3ADisplayVar[nIterator]->contentsMD) + 1); sprintf (buffer,"%d %s %s %d %x %x",Stage3ADisplayVar[nIterator]->nSlot, Stage3ADisplayVar[nIterator]->Item,Stage3ADisplayVar[nIterator]->Type,Stage3ADisplayVar[nIterator]->nIndex,Stage3ADisplayVar[nIterator]->attributesMD,Stage3ADisplayVar[nIterator]->contentsMD); How do I make sure the rows in the file are properly aligned. Thank you.

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  • write 2d array to a file in C (Operating system)

    - by Bobj-C
    Hello All, I used to use the code below to Write an 1D array to a File: FILE *fp; float floatValue[5] = { 1.1F, 2.2F, 3.3F, 4.4F, 5.5F }; int i; if((fp=fopen("test", "wb"))==NULL) { printf("Cannot open file.\n"); } if(fwrite(floatValue, sizeof(float), 5, fp) != 5) printf("File read error."); fclose(fp); /* read the values */ if((fp=fopen("test", "rb"))==NULL) { printf("Cannot open file.\n"); } if(fread(floatValue, sizeof(float), 5, fp) != 5) { if(feof(fp)) printf("Premature end of file."); else printf("File read error."); } fclose(fp); for(i=0; i<5; i++) printf("%f ", floatValue[i]); My question is if i want to write and read 2D array ??

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  • Should we avoid to use Object as the input parameter/ output value of a method?

    - by developer.cyrus
    Take Java syntax as an example, though the question itself is language independent. If the following snippet takes an object MyAbstractEmailTemplate as input argument in the method setTemplate, the class MyGateway will then become tightly-coupled with the object MyAbstractEmailTemplate, which lessens the re-usability of the class MyGateway. A compromise is to use dependency-injection to ease the instantiation of MyAbstractEmailTemplate. This might solve the coupling problem to some extent, but the interface is still rigid, hardly providing enough ?exibility to other developers/ applications. So if we only use primitive data type (or even plain XML in web service) as the input/ output of a method, it seems the coupling problem no longer exists. So what do you think? public class MyGateway { protected MyAbstractEmailTemplate template; publoc void setTemplate(MyAbstractEmailTemplate template) { this.template = template; } }

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  • Reading and writing in parallel

    - by Malfist
    I want to be able to read and write a large file in parallel, or if not in parallel, at least in blocks so that I don't use up so much memory. This is my current code: // Define memory stream which will be used to hold encrypted data. MemoryStream memoryStream = new MemoryStream(); // Define cryptographic stream (always use Write mode for encryption). CryptoStream cryptoStream = new CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write); //start encrypting using (BinaryReader reader = new BinaryReader(File.Open(fileIn, FileMode.Open))) { byte[] buffer = new byte[1024 * 1024]; int read = 0; do { read = reader.Read(buffer, 0, buffer.Length); cryptoStream.Write(buffer, 0, read); } while (read == buffer.Length); } // Finish encrypting. cryptoStream.FlushFinalBlock(); // Convert our encrypted data from a memory stream into a byte array. //byte[] cipherTextBytes = memoryStream.ToArray(); //write our memory stream to a file memoryStream.Position = 0; using (BinaryWriter writer = new BinaryWriter(File.Open(fileOut, FileMode.Create))) { byte[] buffer = new byte[1024 * 1024]; int read = 0; do { read = memoryStream.Read(buffer, 0, buffer.Length); writer.Write(buffer, 0, read); } while (read == buffer.Length); } // Close both streams. memoryStream.Close(); cryptoStream.Close(); As you can see, it reads the entire file into memory, encrypts it, then writes it out. If I happen to be encrypting files that are very large (2GB+) it tends not to work, or at the very least, consumes ~97% of my memory. How could I do it in a more effective manner?

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  • [c++] How to create a std::ofstream to a temp file?

    - by dehmann
    Okay, mkstemp is the preferred way to create a temp file in POSIX. But it opens the file and returns an int, which is a file descriptor. From that I can only create a FILE*, but not an std::ofstream, which I would prefer in C++. (Apparently, on AIX and some other systems, you can create an std::ofstream from a file descriptor, but my compiler complains when I try that.) I know I could get a temp file name with tmpnam and then open my own ofstream with it, but that's apparently unsafe due to race conditions, and results in a compiler warning (g++ v3.4. on Linux): warning: the use of `tmpnam' is dangerous, better use `mkstemp' So, is there any portable way to create an std::ofstream to a temp file?

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  • FileNotFound exception

    - by Pratik
    I am trying to read a file in a servlet. I am using eclipse IDE. I get a FileNotFoundException if I provide relative file name. List<String> ls=new ArrayList<String>(); Scanner input = new Scanner(new File("Input.txt")); while(input.hasNextLine()) { ls.add(input.nextLine()); } The same code works if I put the absolute path like this: Scanner input = new Scanner(new File("F:/Spring and other stuff/AjaxDemo/src/com/pdd/ajax/Input.txt")); The Java file and text file are there in the same folder. Does it searches text file in some other folder ?

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  • File mode for creating+reading+appending+binary

    - by MihaiD
    I need to open a file for reading and writing. If the file is not found, it should be created. It should also be treated as a binary for Windows. Can you tell me the file mode sequence I need to use for this? I tried 'r+ab' but that doesn't create the files if they are not found. Thanks

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  • Exciting new Evented I/O technologies

    - by Saif Bechan
    Lately I have been having my eye on evented I/O to tackle some of my web application problems. I have been looking at things as Python's Twisted, Ruby's Eventmachine, and Node.js. Are there any other alternatives to these three, maybe in other languages as PHP ?

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  • unbuffered I/O in Linux

    - by stuck
    I'm writing lots and lots of data that will not be read again for weeks - as my program runs the amount of free memory on the machine (displayed with 'free' or 'top') drops very quickly, the amount of memory my app uses does not increase - neither does the amount of memory used by other processes. This leads me to believe the memory is being consumed by the filesystems cache - since I do not intend to read this data for a long time I'm hoping to bypass the systems buffers, such that my data is written directly to disk. I dont have dreams of improving perf or being a super ninja, my hope is to give a hint to the filesystem that I'm not going to be coming back for this memory any time soon, so dont spend time optimizing for those cases. On Windows I've faced similar problems and fixed the problem using FILE_FLAG_NO_BUFFERING|FILE_FLAG_WRITE_THROUGH - the machines memory was not consumed by my app and the machine was more usable in general. I'm hoping to duplicate the improvements I've seen but on Linux. On Windows there is the restriction of writing in sector sized pieces, I'm happy with this restriction for the amount of gain I've measured. is there a similar way to do this in Linux?

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  • Reading a large text file to memory in C++

    - by NoneType
    Is there a way to read a large text file (~60MB) into memory at once (like a compiler flag to increase program memory limit) ? Currently, ofstream's open function throws a segmentation fault while trying to read this file. ifstream fis; fis.open("my_large_file.txt"); // Segfaults here The file just consists of rows of the form number_1<tabspace>number_2 i.e., two numbers separated by a tabspace.

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  • How to create custom filenames in C?

    - by eSKay
    Please see this piece of code: #include<stdio.h> #include<string.h> #include<stdlib.h> int main() { int i = 0; FILE *fp; for(i = 0; i < 100; i++) { fp = fopen("/*what should go here??*/","w"); //I need to create files with names: file0.txt, file1.txt, file2.txt etc //i.e. file{i}.txt } }

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  • Python text file processing speed issues

    - by Anonymouslemming
    Hi all, I'm having a problem with processing a largeish file in Python. All I'm doing is f = gzip.open(pathToLog, 'r') for line in f: counter = counter + 1 if (counter % 1000000 == 0): print counter f.close This takes around 10m25s just to open the file, read the lines and increment this counter. In perl, dealing with the same file and doing quite a bit more (some regular expression stuff), the whole process takes around 1m17s. Perl Code: open(LOG, "/bin/zcat $logfile |") or die "Cannot read $logfile: $!\n"; while (<LOG>) { if (m/.*\[svc-\w+\].*login result: Successful\.$/) { $_ =~ s/some regex here/$1,$2,$3,$4/; push @an_array, $_ } } close LOG; Can anyone advise what I can do to make the Python solution run at a similar speed to the Perl solution? I've tried just uncompressing the file and dealing with it using open instead of gzip.open, but that made a very small difference to the overall time.

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  • Seeking to a line in a file in g++

    - by Phenom
    Is there a way that I can seek to a certain line in a file to read or write data? Let's say I want to write some data starting on the 10th line in a text file. There might be some data already in the first few lines, or the file could even be empty. Is there a way I can seek directly to the line I want without having to worry about what's already in the file?

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