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  • Recommendations for a C++ polymorphic, seekable, binary I/O interface

    - by Trevor Robinson
    I've been using std::istream and ostream as a polymorphic interface for random-access binary I/O in C++, but it seems suboptimal in numerous ways: 64-bit seeks are non-portable and error-prone due to streampos/streamoff limitations; currently using boost/iostreams/positioning.hpp as a workaround, but it requires vigilance Missing operations such as truncating or extending a file (ala POSIX ftruncate) Inconsistency between concrete implementations; e.g. stringstream has independent get/put positions whereas filestream does not Inconsistency between platform implementations; e.g. behavior of seeking pass the end of a file or usage of failbit/badbit on errors Don't need all the formatting facilities of stream or possibly even the buffering of streambuf streambuf error reporting (i.e. exceptions vs. returning an error indicator) is supposedly implementation-dependent in practice I like the simplified interface provided by the Boost.Iostreams Device concept, but it's provided as function templates rather than a polymorphic class. (There is a device class, but it's not polymorphic and is just an implementation helper class not necessarily used by the supplied device implementations.) I'm primarily using large disk files, but I really want polymorphism so I can easily substitute alternate implementations (e.g. use stringstream instead of fstream for unit tests) without all the complexity and compile-time coupling of deep template instantiation. Does anyone have any recommendations of a standard approach to this? It seems like a common situation, so I don't want to invent my own interfaces unnecessarily. As an example, something like java.nio.FileChannel seems ideal. My best solution so far is to put a thin polymorphic layer on top of Boost.Iostreams devices. For example: class my_istream { public: virtual std::streampos seek(stream_offset off, std::ios_base::seekdir way) = 0; virtual std::streamsize read(char* s, std::streamsize n) = 0; virtual void close() = 0; }; template <class T> class boost_istream : public my_istream { public: boost_istream(const T& device) : m_device(device) { } virtual std::streampos seek(stream_offset off, std::ios_base::seekdir way) { return boost::iostreams::seek(m_device, off, way); } virtual std::streamsize read(char* s, std::streamsize n) { return boost::iostreams::read(m_device, s, n); } virtual void close() { boost::iostreams::close(m_device); } private: T m_device; };

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  • Write a file in UTF-8 using FileWriter (Java)?

    - by user1280970
    I have the following code however, I want it to write as a UTF-8 file to handle foreign characters. Is there a way of doing this, is there some need to have a parameter? I would really appreciate your help with this. Thanks. try { BufferedReader reader = new BufferedReader(new FileReader("C:/Users/Jess/My Documents/actresses.list")); writer = new BufferedWriter(new FileWriter("C:/Users/Jess/My Documents/actressesFormatted.csv")); while( (line = reader.readLine()) != null) { //If the line starts with a tab then we just want to add a movie //using the current actor's name. if(line.length() == 0) continue; else if(line.charAt(0) == '\t') { readMovieLine2(0, line, surname.toString(), forename.toString()); } //Else we've reached a new actor else { readActorName(line); } } } catch (IOException e) { e.printStackTrace(); } }

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  • How do make my encryption algorithm encrypt more than 128 bits?

    - by Ranhiru
    OK, now I have coded for an implementation of AES-128 :) It is working fine. It takes in 128 bits, encrypts and returns 128 bits So how do i enhance my function so that it can handle more than 128 bits? How do i make the encryption algorithm handle larger strings? Can the same algorithm be used to encrypt files? :) The function definition is public byte[] Cipher(byte[] input) { }

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  • create a sparse BufferedImage in java

    - by elgcom
    I have to create an image with very large resolution, but the image is relatively "sparse", only some areas in the image need to draw. For example with following code /* this take 5GB memory */ final BufferedImage img = new BufferedImage( 36000, 36000, BufferedImage.TYPE_INT_ARGB); /* draw something */ Graphics g = img.getGraphics(); g.drawImage(....); /* output as PNG */ final File out = new File("out.png"); ImageIO.write(img, "png", out); The PNG image on the end I created is ONLY about 200~300 MB. The question is how can I avoid creating a 5GB BufferedImage at the beginning? I do need an image with large dimension, but with very sparse color information. Is there any Stream for BufferedImage so that it will not take so much memory?

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  • Intercept windows open file

    - by HyLian
    Hello, I'm trying to make a small program that could intercept the open process of a file. The purpose is when an user double-click on a file in a given folder, windows would inform to the software, then it process that petition and return windows the data of the file. Maybe there would be another solution like monitoring Open messages and force Windows to wait while the program prepare the contents of the file. One application of this concept, could be to manage desencryption of a file in a transparent way to the user. In this context, the encrypted file would be on the disk and when the user open it ( with double-click on it or with some application such as notepad ), the background process would intercept that open event, desencrypt the file and give the contents of that file to the asking application. It's a little bit strange concept, it could be like "Man In The Middle" network concept, but with files instead of network packets. Thanks for reading.

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  • Create a Stream without having a physical file to create from.

    - by jhorton
    I'm needing to create a zip file containing documents that exist on the server. I am using the .Net Package class to do so, and to create a new Package (which is the zip file) I have to have either a path to a physical file or a stream. I am trying to not create an actual file that would be the zip file, instead just create a stream that would exist in memory or something. My question is how do you instantiate a new Stream (i.e. FileStream, MemoryStream, etc) without having a physical file to instantiate from.

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  • Reading and writing C++ vector to a file

    - by JB
    For some graphics work I need to read in a large amount of data as quickly as possible and would ideally like to directly read and write the data structures to disk. Basically I have a load of 3d models in various file formats which take too long to load so I want to write them out in their "prepared" format as a cache that will load much faster on subsequent runs of the program. Is it safe to do it like this? My worries are around directly reading into the data of the vector? I've removed error checking, hard coded 4 as the size of the int and so on so that i can give a short working example, I know it's bad code, my question really is if it is safe in c++ to read a whole array of structures directly into a vector like this? I believe it to be so, but c++ has so many traps and undefined behavour when you start going low level and dealing directly with raw memory like this. I realise that number formats and sizes may change across platforms and compilers but this will only even be read and written by the same compiler program to cache data that may be needed on a later run of the same program. #include <fstream> #include <vector> using namespace std; struct Vertex { float x, y, z; }; typedef vector<Vertex> VertexList; int main() { // Create a list for testing VertexList list; Vertex v1 = {1.0f, 2.0f, 3.0f}; list.push_back(v1); Vertex v2 = {2.0f, 100.0f, 3.0f}; list.push_back(v2); Vertex v3 = {3.0f, 200.0f, 3.0f}; list.push_back(v3); Vertex v4 = {4.0f, 300.0f, 3.0f}; list.push_back(v4); // Write out a list to a disk file ofstream os ("data.dat", ios::binary); int size1 = list.size(); os.write((const char*)&size1, 4); os.write((const char*)&list[0], size1 * sizeof(Vertex)); os.close(); // Read it back in VertexList list2; ifstream is("data.dat", ios::binary); int size2; is.read((char*)&size2, 4); list2.resize(size2); // Is it safe to read a whole array of structures directly into the vector? is.read((char*)&list2[0], size2 * sizeof(Vertex)); }

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  • Reading a Delphi binary file in Python

    - by Brendan
    I have a file that was written with the following Delphi declaration ... Type Tfulldata = Record dpoints, dloops : integer; dtime, bT, sT, hI, LI : real; tm : real; data : array[1..armax] Of Real; End; ... Var: fh: File Of Tfulldata; I want to analyse the data in the files (many MB in size) using Python if possible - is there an easy way to read in the data and cast the data into Python objects similar in form to the Delphi records? Does anyone know of a library perhaps that does this?

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  • Execute a Application On The Server Using VBScript

    - by Nathan Campos
    I have an application on my server that is called leaf.exe, that haves two arguments needed to run, they are: inputfile and outputfile, that will be like this example: leaf.exe input.jpg output.leaf They are all on the same directory as my home page file(the executable and the input file). But I need that a VBScript could run the application like that, then I want to know how could I do this.

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  • Extract some data from a lot of xml files

    - by LifeH2O
    I have cricket player profiles saved in the form of .xml files in a folder. each file has these tags in it <playerid>547</playerid> <majorteam>England</majorteam> <playername>Don</playername> the playerid is same as in .xml (each file is of different size,1kb to 5kb). These are about 500 files. What i need is to extract the playername, majorteam, and playerid from all these files to a list. I will convert that list to XML later. If you know how can i do it directly to XML i will be very thankful.

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  • Quickest way to write to file in java

    - by user1097772
    I'm writing an application which compares directory structure. First I wrote an application which writes gets info about files - one line about each file or directory. My soulution is: calling method toFile Static PrintWriter pw = new PrintWriter(new BufferedWriter( new FileWriter("DirStructure.dlis")), true); String line; // info about file or directory public void toFile(String line) { pw.println(line); } and of course pw.close(), at the end. My question is, can I do it quicker? What is the quickest way? Edit: quickest way = quickest writing in the file

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  • Read file from root directory folder using filestream

    - by SurajSing
    There are two Image files in my folder which I have to call in my program. I have used: AppDomain.curentDomain.baseDirectory + "Path and file name"; But this goes into my bin directory which I don't want; I want to read the folder from root directory where my folder name as resource I have saved my file there and call the image so please what's the code for that? How do I read from root directory in a Windows Form Application?

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  • Why isn't this file reading/writing program working?

    - by user320950
    This program is supposed to read files and write them. I took the file open checks out because they kept causing errors. The problem is that the files open like they are supposed to and the names are correct but nothing is on any of the text screens. Do you know what is wrong? #include<iostream> #include<fstream> #include<cstdlib> #include<iomanip> using namespace std; int main() { ifstream in_stream; // reads itemlist.txt ofstream out_stream1; // writes in items.txt ifstream in_stream2; // reads pricelist.txt ofstream out_stream3;// writes in plist.txt ifstream in_stream4;// read recipt.txt ofstream out_stream5;// write display.txt float price=' ',curr_total=0.0; int wrong=0; int itemnum=' '; char next; in_stream.open("ITEMLIST.txt", ios::in); // list of avaliable items out_stream1.open("listWititems.txt", ios::out); // list of avaliable items in_stream2.open("PRICELIST.txt", ios::in); out_stream3.open("listWitdollars.txt", ios::out); in_stream4.open("display.txt", ios::in); out_stream5.open("showitems.txt", ios::out); in_stream.close(); // closing files. out_stream1.close(); in_stream2.close(); out_stream3.close(); in_stream4.close(); out_stream5.close(); system("pause"); in_stream.setf(ios::fixed); while(in_stream.eof()) { in_stream >> itemnum; cin.clear(); cin >> next; } out_stream1.setf(ios::fixed); while (out_stream1.eof()) { out_stream1 << itemnum; cin.clear(); cin >> next; } in_stream2.setf(ios::fixed); in_stream2.setf(ios::showpoint); in_stream2.precision(2); while((price== (price*1.00)) && (itemnum == (itemnum*1))) { while (in_stream2 >> itemnum >> price) // gets itemnum and price { while (in_stream2.eof()) // reads file to end of file { in_stream2 >> itemnum; in_stream2 >> price; price++; curr_total= price++; in_stream2 >> curr_total; cin.clear(); // allows more reading cin >> next; } } } out_stream3.setf(ios::fixed); out_stream3.setf(ios::showpoint); out_stream3.precision(2); while((price== (price*1.00)) && (itemnum == (itemnum*1))) { while (out_stream3 << itemnum << price) { while (out_stream3.eof()) // reads file to end of file { out_stream3 << itemnum; out_stream3 << price; price++; curr_total= price++; out_stream3 << curr_total; cin.clear(); // allows more reading cin >> next; } return itemnum, price; } } in_stream4.setf(ios::fixed); in_stream4.setf(ios::showpoint); in_stream4.precision(2); while ( in_stream4.eof()) { in_stream4 >> itemnum >> price >> curr_total; cin.clear(); cin >> next; } out_stream5.setf(ios::fixed); out_stream5.setf(ios::showpoint); out_stream5.precision(2); out_stream5 <<setw(5)<< " itemnum " <<setw(5)<<" price "<<setw(5)<<" curr_total " <<endl; // sends items and prices to receipt.txt out_stream5 << setw(5) << itemnum << setw(5) <<price << setw(5)<< curr_total; // sends items and prices to receipt.txt out_stream5 << " You have a total of " << wrong++ << " errors " << endl; }

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  • Why does C's "fopen" take a "const char *" as its second argument?

    - by Chris Cooper
    It has always struck me as strange that the C function "fopen" takes a "const char *" as the second argument. I would think it would be easier to both read your code and implement the library's code if there were bit masks defined in stdio.h, like "IO_READ" and such, so you could do things like: FILE* myFile = fopen("file.txt", IO_READ & IO_WRITE); Is there a programmatic reason for the way it actually is, or is it just historic? (i.e. "That's just the way it is.")

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  • Java- FileWriter/BufferedWriter - appending to end of a text file?

    - by KP65
    I've done this before once, I'm trying to replicate what I did so far and this is what I've got: try { BufferedWriter writer = new BufferedWriter(new FileWriter("file.P", true)); System.out.println("entered"); if (!(newUserName.isEmpty()) || (newUserPass.isEmpty())){ writer.newLine(); writer.write("hellotest123"); writer.close(); } It seems to find file.P, which is just a txt file, but it doesn't seem to append anything onto it? It enters the code and passes the IF statement fine, but nothing is appended to the text file? I'm slightly stuck!

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  • File Output using Gforth

    - by sheepez
    As a first project I have been writing a short program to render the Mandelbrot fractal. I have got to the point of trying to output my results to a file ( e.g. .bmp or .ppm ) and got stuck. I have not really found any examples of exactly what I am trying to do, but I have found two examples of code to copy from one file to another. The examples in the Gforth documentation ( Section 3.27 ) did not work for me ( winXP ) in fact they seemed to open and create files but not write to files properly. This is the Gforth documentation example that copies the contents of one file to another: 0 Value fd-in 0 Value fd-out : open-input ( addr u -- ) r/o open-file throw to fd-in ; : open-output ( addr u -- ) w/o create-file throw to fd-out ; s" foo.in" open-input s" foo.out" open-output : copy-file ( -- ) begin line-buffer max-line fd-in read-line throw while line-buffer swap fd-out write-line throw repeat ; I found this example ( http://rosettacode.org/wiki/File_IO#Forth ) which does work. The main problem is that I can't isolate the part that writes to a file and have it still work. The main confusion is that r doesn't seem to consume TOS as I might expect. : copy-file2 ( a1 n1 a2 n2 -- ) r/o open-file throw >r w/o create-file throw r> begin pad maxstring 2 pick read-file throw ?dup while pad swap 3 pick write-file throw repeat close-file throw close-file throw ; \ Invoke it like this: s" output.txt" s" input.txt" copy-file I would be very grateful if someone could explain exactly how the open, create read and write -file words actually work, as my investigation keeps resulting in somewhat bizarre stacks. Any clues as to why the Gforth examples do not work might help too. In summary, I want to output from Gforth to a file and so far have been thwarted. Can anyone offer any help? Thank you Vijay, I think that I understand the example that you gave. However when I try to use something like this ( which I think is similar ): 0 value test-file : write-test s" testfile.out" w/o create-file throw to test-file s" test text" test-file write-line ; I get ok but nothing is put into the file, have I made a mistake? It seems that the problem was due to not flushing the relevant buffers or explicitly closing the file. Adding something like test-file flush-file throw or test-file close-file throw between write-line and ; makes it work. Thanks again Vijay for helping.

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  • Unable to open a file for writing

    - by asdasdas
    I am trying to write to a file. I do a file_exists check on it before I do fopen and it returns true (the file does exist). However, the file fails this code and gives me the error every time: $handle = fopen($filename, 'w'); if($handle) { flock($handle, LOCK_EX); fwrite($handle, $contents); } else { echo 'ERROR: Unable to open the file for writing.',PHP_EOL; exit(); } flock($handle, LOCK_UN); fclose($handle); Is there a way I can get more specific error details as to why this file does not let me open it for writing? I know that the filename is legit, but for some reason it just wont let me write to it. I do have write permissions, I was able to write and write over another file.

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  • What is the magic behind perl read() function and buffer which is not a ref ?

    - by alex8657
    I do not get to understand how the Perl read($buf) function is able to modify the content of the $buf variable. $buf is not a reference, so the parameter is given by copy (from my c/c++ knowledge). So how come the $buf variable is modified in the caller ? Is it a tie variable or something ? The C documentation about setbuf is also quite elusive and unclear to me # Example 1 $buf=''; # It is a scalar, not a ref $bytes = $fh->read($buf); print $buf; # $buf was modified, what is the magic ? # Example 2 sub read_it { my $buf = shift; return $fh->read($buf); } my $buf; $bytes = read_it($buf); print $buf; # As expected, this scope $buf was not modified

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  • Files written with FileWriter are either 32 KB, 24 KB, 16 KB, ... big or empty

    - by Bernhard V
    Hi, I read a file into a string, change the first line and then write this string into a new file. I do this through the following code (a little bit shortened): while(jspIterator.hasNext()){ String line = (String) jspIterator.next(); if (i == 0) { if (line.startsWith("bla bla") && line.endsWith("yada")) { line = line.replaceFirst("this", "that"); } } jspAsString += line; i++; } FileWriter newJspWriter = new FileWriter(newJspFile); newJspWriter.write(jspAsString); Now the files written this way are either 32, 24, 16, 8 KByte big or completely empty. When debugging I see that the String is assembled correctly. When I print the variable jspAsString to the console it also appears correct. Do you know why FileWriter behaves this way?

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  • Java Client-Server problem when sending multiple files

    - by Jim
    Client public void transferImage() { File file = new File(ServerStats.clientFolder); String[] files = file.list(); int numFiles = files.length; boolean done = false; BufferedInputStream bis; BufferedOutputStream bos; int num; byte[] byteArray; long count; long len; Socket socket = null ; while (!done){ try{ socket = new Socket(ServerStats.imgServerName,ServerStats.imgServerPort) ; InputStream inStream = socket.getInputStream() ; OutputStream outStream = socket.getOutputStream() ; System.out.println("Connected to : " + ServerStats.imgServerName); BufferedReader inm = new BufferedReader(new InputStreamReader(inStream)); PrintWriter out = new PrintWriter(outStream, true /* autoFlush */); for (int itor = 0; itor < numFiles; itor++) { String fileName = files[itor]; System.out.println("transfer: " + fileName); File sentFile = new File(fileName); len = sentFile.length(); len++; System.out.println(len); out.println(len); out.println(sentFile); //SENDFILE bis = new BufferedInputStream(new FileInputStream(fileName)); bos = new BufferedOutputStream(socket.getOutputStream( )); byteArray = new byte[1000000]; count = 0; while ( count < len ){ num = bis.read(byteArray); bos.write(byteArray,0,num); count++; } bos.close(); bis.close(); System.out.println("file done: " + itor); } done = true; }catch (Exception e) { System.err.println(e) ; } } } Server public static void main(String[] args) { BufferedInputStream bis; BufferedOutputStream bos; int num; File file = new File(ServerStats.serverFolder); if (!(file.exists())){ file.mkdir(); } try { int i = 1; ServerSocket socket = new ServerSocket(ServerStats.imgServerPort); Socket incoming = socket.accept(); System.out.println("Spawning " + i); try { try{ if (!(file.exists())){ file.mkdir(); } InputStream inStream = incoming.getInputStream(); OutputStream outStream = incoming.getOutputStream(); BufferedReader inm = new BufferedReader(new InputStreamReader(inStream)); PrintWriter out = new PrintWriter(outStream, true /* autoFlush */); String length2 = inm.readLine(); System.out.println(length2); String filename = inm.readLine(); System.out.println("Filename = " + filename); out.println("ACK: Filename received = " + filename); //RECIEVE and WRITE FILE byte[] receivedData = new byte[1000000]; bis = new BufferedInputStream(incoming.getInputStream()); bos = new BufferedOutputStream(new FileOutputStream(ServerStats.serverFolder + "/" + filename)); long length = (long)Integer.parseInt(length2); length++; long counter = 0; while (counter < length){ num = bis.read(receivedData); bos.write(receivedData,0,num); counter ++; } System.out.println(counter); bos.close(); bis.close(); File receivedFile = new File(filename); long receivedLen = receivedFile.length(); out.println("ACK: Length of received file = " + receivedLen); } finally { incoming.close(); } } catch (IOException e){ e.printStackTrace(); } } catch (IOException e1){ e1.printStackTrace(); } } The code is some I found, and I have slightly modified it, but I am having problems transferring multiple images over the server. Output on Client: run ServerQueue.Client Connected to : localhost transfer: Picture 012.jpg 1312743 java.lang.ArrayIndexOutOfBoundsException Connected to : localhost transfer: Picture 012.jpg 1312743 Cant seem to get it to transfer multiple images. But bothsides I think crash or something because the file never finishes transfering

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  • Write problem - lossing the original data

    - by John
    Every time I write to the text file I will lose the original data, how can I read the file and enter the data in the empty line or the next line which is empty? public void writeToFile() { try { output = new Formatter(myFile); } catch(SecurityException securityException) { System.err.println("Error creating file"); System.exit(1); } catch(FileNotFoundException fileNotFoundException) { System.err.println("Error creating file"); System.exit(1); } Scanner scanner = new Scanner (System.in); String number = ""; String name = ""; System.out.println("Please enter number:"); number = scanner.next(); System.out.println("Please enter name:"); name = scanner.next(); output.format("%s,%s \r\n", number, name); output.close(); }

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