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• Are fopen/fread/fgets PID-safe in C ?

  - by Jane

  Various users are browsing through a website 100% programmed in C (CGI). Each webpage uses fopen/fgets/fread to read common data (like navigation bars) from files. Would each call to fopen/fgets/fread interefere with each other if various people are browsing the same page ? If so, how can this be solved in C ? (This is a Linux server, compiling is done with gcc and this is for a CGI website programmed in C.) Example: FILE *DATAFILE = fopen(PATH, "r"); if ( DATAFILE != NULL ) { while ( fgets( LINE, BUFFER, DATAFILE ) ) { /* do something */ } }

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• How to send large objects using boost::asio

  - by Max

  Good day. I'm receiving a large objects via the net using boost::asio. And I have a code: for (int i = 1; i <= num_packets; i++) boost::asio::async_read(socket_, boost::asio::buffer(Obj + packet_size * (i - 1), packet_size), boost::bind(...)); Where My_Class * Obj. I'm in doubt if that approach possible (because i have a pointer to an object here)? Or how it would be better to receive this object using packets of fixed size in bytes? Thanks in advance.

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• What is stopping data flow with .NET 3.5 asynchronous System.Net.Sockets.Socket?

  - by TonyG

  I have a .NET 3.5 client/server socket interface using the asynchronous methods. The client connects to the server and the connection should remain open until the app terminates. The protocol consists of the following pattern: send stx receive ack send data1 receive ack send data2 (repeat 5-6 while more data) receive ack send etx So a single transaction with two datablocks as above would consist of 4 sends from the client. After sending etx the client simply waits for more data to send out, then begins the next transmission with stx. I do not want to break the connection between individual exchanges or after each stx/data/etx payload. Right now, after connection, the client can send the first stx, and get a single ack, but I can't put more data onto the wire after that. Neither side disconnects, the socket is still intact. The client code is seriously abbreviated as follows - I'm following the pattern commonly available in online code samples. private void SendReceive(string data) { // ... SocketAsyncEventArgs completeArgs; completeArgs.Completed += new EventHandler<SocketAsyncEventArgs>(OnSend); clientSocket.SendAsync(completeArgs); // two AutoResetEvents, one for send, one for receive if ( !AutoResetEvent.WaitAll(autoSendReceiveEvents , -1) ) Log("failed"); else Log("success"); // ... } private void OnSend( object sender , SocketAsyncEventArgs e ) { // ... Socket s = e.UserToken as Socket; byte[] receiveBuffer = new byte[ 4096 ]; e.SetBuffer(receiveBuffer , 0 , receiveBuffer.Length); e.Completed += new EventHandler<SocketAsyncEventArgs>(OnReceive); s.ReceiveAsync(e); // ... } private void OnReceive( object sender , SocketAsyncEventArgs e ) {} // ... if ( e.BytesTransferred > 0 ) { Int32 bytesTransferred = e.BytesTransferred; String received = Encoding.ASCII.GetString(e.Buffer , e.Offset , bytesTransferred); dataReceived += received; } autoSendReceiveEvents[ SendOperation ].Set(); // could be moved elsewhere autoSendReceiveEvents[ ReceiveOperation ].Set(); // releases mutexes } The code on the server is very similar except that it receives first and then sends a response - the server is not doing anything (that I can tell) to modify the connection after it sends a response. The problem is that the second time I hit SendReceive in the client, the connection is already in a weird state. Do I need to do something in the client to preserve the SocketAsyncEventArgs, and re-use the same object for the lifetime of the socket/connection? I'm not sure which eventargs object should hang around during the life of the connection or a given exchange. Do I need to do something, or Not do something in the server to ensure it continues to Receive data? The server setup and response processing looks like this: void Start() { // ... listenSocket.Bind(...); listenSocket.Listen(0); StartAccept(null); // note accept as soon as we start. OK? mutex.WaitOne(); } void StartAccept(SocketAsyncEventArgs acceptEventArg) { if ( acceptEventArg == null ) { acceptEventArg = new SocketAsyncEventArgs(); acceptEventArg.Completed += new EventHandler<SocketAsyncEventArgs>(OnAcceptCompleted); } Boolean willRaiseEvent = this.listenSocket.AcceptAsync(acceptEventArg); if ( !willRaiseEvent ) ProcessAccept(acceptEventArg); // ... } private void OnAcceptCompleted( object sender , SocketAsyncEventArgs e ) { ProcessAccept(e); } private void ProcessAccept( SocketAsyncEventArgs e ) { // ... SocketAsyncEventArgs readEventArgs = new SocketAsyncEventArgs(); readEventArgs.SetBuffer(dataBuffer , 0 , Int16.MaxValue); readEventArgs.Completed += new EventHandler<SocketAsyncEventArgs>(OnIOCompleted); readEventArgs.UserToken = e.AcceptSocket; dataReceived = ""; // note server is degraded for single client/thread use // As soon as the client is connected, post a receive to the connection. Boolean willRaiseEvent = e.AcceptSocket.ReceiveAsync(readEventArgs); if ( !willRaiseEvent ) this.ProcessReceive(readEventArgs); // Accept the next connection request. this.StartAccept(e); } private void OnIOCompleted( object sender , SocketAsyncEventArgs e ) { // switch ( e.LastOperation ) case SocketAsyncOperation.Receive: ProcessReceive(e); // similar to client code // operate on dataReceived here case SocketAsyncOperation.Send: ProcessSend(e); // similar to client code } // execute this when a data has been processed into a response (ack, etc) private SendResponseToClient(string response) { // create buffer with response // currentEventArgs has class scope and is re-used currentEventArgs.SetBuffer(sendBuffer , 0 , sendBuffer.Length); Boolean willRaiseEvent = currentClient.SendAsync(currentEventArgs); if ( !willRaiseEvent ) ProcessSend(currentEventArgs); } A .NET trace shows the following when sending ABC\r\n: Socket#7588182::SendAsync() Socket#7588182::SendAsync(True#1) Data from Socket#7588182::FinishOperation(SendAsync) 00000000 : 41 42 43 0D 0A Socket#7588182::ReceiveAsync() Exiting Socket#7588182::ReceiveAsync() - True#1 And it stops there. It looks just like the first send from the client but the server shows no activity. I think that could be info overload for now but I'll be happy to provide more details as required. Thanks!

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• Piping SoX in Python - subprocess alternative?

  - by Cochise Ruhulessin

  I use SoX in an application. The application uses it to apply various operations on audiofiles, such as trimming. This works fine: from subprocess import Popen, PIPE kwargs = {'stdin': PIPE, 'stdout': PIPE, 'stderr': PIPE} pipe = Popen(['sox','-t','mp3','-', 'test.mp3','trim','0','15'], **kwargs) output, errors = pipe.communicate(input=open('test.mp3','rb').read()) if errors: raise RuntimeError(errors) This will cause problems on large files hower, since read() loads the complete file to memory; which is slow and may cause the pipes' buffer to overflow. A workaround exists: from subprocess import Popen, PIPE import tempfile import uuid import shutil import os kwargs = {'stdin': PIPE, 'stdout': PIPE, 'stderr': PIPE} tmp = os.path.join(tempfile.gettempdir(), uuid.uuid1().hex + '.mp3') pipe = Popen(['sox','test.mp3', tmp,'trim','0','15'], **kwargs) output, errors = pipe.communicate() if errors: raise RuntimeError(errors) shutil.copy2(tmp, 'test.mp3') os.remove(tmp) So the question stands as follows: Are there any alternatives to this approach, aside from writing a Python extension to the Sox C API?

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• How to return an image in an HTTP response with CherryPy

  - by colinmarc

  I have code which generates a Cairo ImageSurface, and I expose it like so: def preview(...): surface = cairo.ImageSurface(cairo.FORMAT_ARGB32, width, height) ... cherrypy.response.headers['Content-Type'] = "image/png" return surface.get_data() preview.exposed = True This doesn't work (browsers report that the image has errors). I've tested that surface.write_to_png('test.png') works, but I'm not sure what to dump the data into to return it. I'm guessing some file-like object? According to the pycairo documentation, get_data() returns a buffer. I've also now tried: tempf = os.tmpfile() surface.write_to_png(tempf) return tempf Also, is it better to create and hold this image in memory (like I'm trying to do) or write it to disk as a temp file and serve it from there? I only need the image once, then it can be discarded.

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• Flash FLVPlayback states

  - by rob5408

  I'm writing my own class to manage a skin for an FLVPlayback component. It works 90% of the time, but sometimes the state get really messed up. Specifically, the video is playing, meaning I can see it play and the VideoEvent.PLAYHEAD_UPDATE event is firing, but when I poll the FLVPlayback component about its playing property, it returns false. I assume this may be because 'buffering' is kind of a subset of 'playing', but I cannot confirm this in the documentation. I guess another way to ask this question is, "Does the FLVPlayback component ever buffer while it is in a stopped state?"

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• Async Socket Listener on separate thread - VB.net

  - by TheHockeyGeek

  I am trying to use the code from Microsoft for an Async Socket connection. It appears the listener runs in the main thread locking the GUI. I am new at both socket connections and multi-threading all at the same time. Having a hard time getting my mind wrapped around this all at once. The code used is at http://msdn.microsoft.com/en-us/library/fx6588te.aspx Using this example, how can I move the listener to its own thread? Public Shared Sub Main() ' Data buffer for incoming data. Dim bytes() As Byte = New [Byte](1023) {} ' Establish the local endpoint for the socket. Dim ipHostInfo As IPHostEntry = Dns.GetHostEntry(Dns.GetHostName()) Dim ipAddress As IPAddress = ipHostInfo.AddressList(1) Dim localEndPoint As New IPEndPoint(ipAddress, 11000) ' Create a TCP/IP socket. Dim listener As New Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp) ' Bind the socket to the local endpoint and listen for incoming connections. listener.Bind(localEndPoint) listener.Listen(100)

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• mod_wsgi | linux installation error

  - by MMRUser

  I'm getting the following error when I try to install mod_wsgi ./configure checking for apxs2... no checking for apxs... /usr/sbin/apxs checking Apache version... 2.2.3 configure: creating ./config.status config.status: creating Makefile make /usr/sbin/apxs -c -I/usr/local/include/python2.6 -DNDEBUG mod_wsgi.c -L/usr/local/lib -L/usr/local/lib/python2.6/config -lpython2.6 -lpthread -ldl -lutil -lm /apr-1/build/libtool --silent --mode=compile gcc -prefer-pic -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m32 -march=i386 -mtune=generic -fasynchronous-unwind-tables -fno-strict-aliasing -DLINUX=2 -D_REENTRANT -D_GNU_SOURCE -D_LARGEFILE64_SOURCE -pthread -I/usr/include/httpd -I/usr/include/apr-1 -I/usr/include/apr-1 -I/usr/local/include/python2.6 -DNDEBUG -c -o mod_wsgi.lo mod_wsgi.c && touch mod_wsgi.slo sh: /apr-1/build/libtool: No such file or directory apxs:Error: Command failed with rc=8323072 . make: *** [mod_wsgi.la] Error 1 libtool is installed on my system.. mod_wsgi 3.2 *Apache 2.2* *Python 2.6*

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• Render view as string then redirect.

  - by JohnRudolfLewis

  In my ASP.NET MVC application, I would like my controller action to render a view to a string, send an email using that string as the body, then do a redirect. I've found several articles here on SO and elsewhere on how to render the view to a string. That part was easy. But when I attempt to perform the redirect, I get an HttpException: Cannot redirect after HTTP headers have been sent. I've tried setting Response.Buffer and Response.BufferOutput to true, I've tried Response.Clear, nothing seems to work. Is it possible to render a view to a string, then do a redirect?

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• Android PCM Bytes

  - by Pintac

  Hi I am using the AudioRecord class to analize raw pcm bytes as it comes in the mic. So thats working nicely. Now i need convert the pcm bytes into decibel. I have a formula that takes sound presure in Pa into db. db = 20 * log10(Pa/ref Pa) So the question is the bytes i am getting from audiorecorder from the buffer what is it is it amplitude pascal sound pressure or what. I tried to putting the value into te formula but it comes back with very hight db so i do not think its right thanks

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• Scroll up/down while selecting multi-page block of text in Vim through putty

  - by shan23

  I'm using vim 6.3.81 on a xterm through putty. When I use set mouse=a , I can scroll through the file , but not select text. When mouse is disabled using set mouse=, I can select text with mouse (automatically copied to a buffer) , but if the text block is over one page long , I can't scroll up/down (and have to select text one screen at a time) !! Is there any way to have the best of both - while selecting text with mouse , if i reach the end of page , it automatically scrolls up/down depending on whether i've reached top/bottom of page and allows me to select text from the next page as well ? I know vim is powerful/flexible enough to do what I want - I just don't know how !! Can anyone help ?

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• Fast, lightweight XML parser

  - by joe90

  I have a specific format XML document that I will get pushed. This document will always be the same type so it's very strict. I need to parse this so that I can convert it into JSON (well, a slightly bastardized version so someone else can use it with DOJO). My question is, shall I use a very fast lightweight (no need for SAX, etc.) XML parser (any ideas?) or write my own, basically converting into a StringBuffer and spinning through the array? Basically, under the covers I assume all HTML parsers will spin thru the string (or memory buffer) and parse, producing output on the way through. Thanks //edit Thanks for the responses so far :) The xml will be between 3/4 lines to about 50 max (at the extreme)..

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• What is the best way to marshal a char array function argument?

  - by Seh Hui 'Felix' Leong

  Let say that given the following signature in LegacyLib.dll: int Login(SysInst *inst, char username[8], char password[6]); The simple way to marshal this function in C# would be: [DllImport("LegacyLib.dll", CharSet=CharSet.Ansi)] public static extern int Login(ref SysInst inst, string username, string password); The problem of doing it in a such a naive way is that the managed string we passed into the username or password parameter could be longer than the array bounds and this could potentially cause a buffer overrun in LegacyLib.dll. Is there a better way which overcomes this problem? i.e. is there any quick [MarshalAs(…)] magic that I could use to counter that?

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• openssl ssl encryption

  - by deddihp

  Hello, I want to discuss about openssl write and read method. Assume I have an data structure like below: /-----------------------------------------------------\ | my_header | PAYLOAD | \-----------------------------------------------------/ | | \ / \ / not encrypted encrypted I think the proper algorithm would be like this : SEND: build my_header with my own header. encrypt PAYLOAD with encryption function attach my_header and PAYLOAD (encrypted) to one buffer send it using common POSIX function just like send or sendto RECV: using common POSIX function just like recv or recvfrom. extract my_header and PAYLOAD(encrypted) decrypt PAYLOAD with decryption function at last i got my_header and PAYLOAD(decrypted). How is your approach if you face a problem like above. Since openssl encrypt all of data that is sent to SSL_write function (CMIIW). Thanks

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• STOP ERASING MY QUESTIONS! - VIEWING FIRST_ROWS BEFORE QUERY COMPLETES (RE-VISITED)

  - by Frank Developer

  OK, so say I have a table with 500K rows, then I ad-hoc query with unsupported indexing which requires a full table scan. I would like to immediately view the first rows returned while the full table scan continues. Then I want to scroll thru the next results. In the meantime, I would like to display the progress of the table scan, example: "SEARCHING.. FOUND 23 OF 500,000 ROWS SO FAR". If I scroll too far ahead, I want to display a message like: "REACHED LAST ROW IN LOOK-AHEAD BUFFER.. QUERY HAS NOT COMPLETED".. Can this be done? Maybe like: spawn/exec, declare scroll cursor, open, fetch, etc.?

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• How do you use vim's quickfix feature?

  - by hora

  I'm a pretty new Vim user and I've found that its learning curve is quite steep (at least for me). I just installed this vim script for JavaScriptLint error checking, which shows errors in vim's quickfix window once I save a buffer. However, I don't know what to do next.. How do I 'scroll' through all the errors? How do I close the quickfix 'window'? How do I get it to check for errors after I've made changes to my code? I've looked at the vim quickfix docs but the amount of commands are overwhelming and I can't seem to find what I want. Any help would be appreciated. A side question: is there any way to have javascriptlint check for js errors for code residing in a .html file? Thanks!

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• Slime in emacs seems has conflicts with autopair

  - by Boris

  I have just install slime in emacs. And after removed all the other plugins for debuging, I found that slime seems had conflicts with autopair.(Or a bug of autopair?).In slime, when I typed C-c C-c, the minibuffer displayed error like: error in process filter: define-key: Wrong type argument: characterp, nil error in process filter: Wrong type argument: characterp, nil error in process filter: define-key: Wrong type argument: characterp, nil error in process filter: Wrong type argument: characterp, nil Even more, the error message still alerted after I killed the slime buffer. If I also remove the autopair plugin, slime works just fine. Can anyone tell me how to solve this? Thanks. :)

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• Move entire line up and down in Vim

  - by guy.incognito

  In Notepad++, I can use ctrl + shift + up/down to move the current line up and down. Is there a similar command to this in Vim? I have looked through endless guides, but have found nothing. If there isn't, how could I bind the action to that key combination? Edit: Mykola's answer works for all lines, apart from those at the beginning and end of the buffer. Moving the first line up or the bottom line down deletes the line, and when moving the bottom line up it jumps two spaces initially, like a pawn! Can anyone offer any refinements?

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• Is it possible to avoid downloading song up to the supplied position using SoundManager2?

  - by dinjas

  I'm using the SoundManager2 JavaScript SDK on a site that streams synchronized audio from SoundCloud to multiple clients simultaneously. When a new user loads the page, the audio is loaded, and a position parameter is set to specify where playback should begin. The problem arises when the track is really long (say 60 minutes), and the current track position is substantially far into the track (e.g. 30 minutes). When this is the case, it takes a really long time before playback begins because the track has to download/buffer up to the current position. Is there a way to avoid downloading the 30 minutes of audio that I don't need?

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• Drawing individual pixels with iphone sdk.

  - by blob8108

  Hi, I've been trying to figure out how to make a powder toy style game on the iPhone. My problem is how to draw pixels to the screen. From what I've read, OpenGL is better for games as it is faster/hardware accelerated, but there is no method to draw pixels directly to the screen. Apparently drawing pixels to an off-screen frame buffer is the way to go, but how do I then pass this to OpenGL? Do I use a texture? (this is assuming I have no previous knowledge of iPhone graphics programming). Thanks!

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• Is there a way to log when a particular memory location gets written and by which function?

  - by rusbi

  I'm having a bug in my c++ program which happens very rarely but crashes my program. It's seems I have some buffer overflow problem or something similar. I find that these types of bug are most difficult to find. My program always crashes because of the same corrupted memory location. I'm wondering if there is some debugging tool which could detect when a particular memory location get written to and logs the function which does it. I'm using VLD (visual leak detector) for my memory leak hunting and it works great. It substitutes the original mallocs which its own and logs every allocation. I was wondering if there is something similar for memory? I know that something like that would cripple a program, but it could be really helpful.

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• How to use ctrl-i for an emacs shortcut without breaking tabs

  - by mksuth

  I want to redefine the emacs keyboard shortcut control-i to be "MOVE CURSOR UP" To do this, I added the following line to my .emacs file: (global-set-key (kbd "C-i") 'previous-line) What I then discovered is that the tab key, by default, does whatever is bound to control-i, which is obviously not what I want. So, to restore normal tab behavior, I added this to my .emacs file (global-set-key (kbd "<tab>") 'indent-for-tab-command) This mostly works. BUT, tab no longer works for auto-completing commands in the mini buffer. How can I fix that? Or is there a better way of going about this? Thanks.

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• Should I use uint in C# for values that can't be negative?

  - by Johannes Rössel

  I have just tried implementing a class where numerous length/count properties, etc. are uint instead of int. However, while doing so I noticed that it's actually painful to do so, like as if no one actually wants to do that. Nearly everything that hands out an integral type returns an int, therefore requiring casts in several points. I wanted to construct a StringBuffer with its buffer length defaulted to one of the fields in that class. Requires a cast too. So I wondered whether I should just revert to int here. I'm certainly not using the entire range anyway. I just thought since what I'm dealing with there simply can't be negative (if it was, it'd be an error) it'd be a nice idea to actually use uint. P.S.: I saw this question and this at least explains why the framework itself always uses int but even in own code it's actually cumbersome to stick to uint which makes me think it apparently isn't really wanted.

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• Is it possible to call a user-space callback function from kernel space in Linux (ioctl)?

  - by Makis

  Is it possible to expand the ioctl interface in Linux so that the user-space application can send a pointer to a function to the kernel space driver? I'm in particular thinking of ways to handle the stream in user-controllable way but doing it in the kernel. Those operations could be attached to the kernel module but this would make development a lot easier as I wouldn't need to mess with the kernel during development. More specifically, this would be the process: Data is read by the driver to a buffer. Data is handled by these user-defined functions in place. Some more handling is done, possibly with some HW blocks. Data is used by a user-space application.

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• match at the beginning of any line, including the first

  - by JoelFan

  According the the Perl documentation on regexes: By default, the "^" character is guaranteed to match only the beginning of the string ... Embedded newlines will not be matched by "^" ... You may, however, wish to treat a string as a multi-line buffer, such that the "^" will match after any newline within the string ... you can do this by using the /m modifier on the pattern match operator. The "after any newline" part means that it will only match at the beginning of the 2nd and subsequent lines. What if I want to match at the beginning of any line (1st, 2nd, etc.)?

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