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  • What limits scaling in this simple OpenMP program?

    - by Douglas B. Staple
    I'm trying to understand limits to parallelization on a 48-core system (4xAMD Opteron 6348, 2.8 Ghz, 12 cores per CPU). I wrote this tiny OpenMP code to test the speedup in what I thought would be the best possible situation (the task is embarrassingly parallel): // Compile with: gcc scaling.c -std=c99 -fopenmp -O3 #include <stdio.h> #include <stdint.h> int main(){ const uint64_t umin=1; const uint64_t umax=10000000000LL; double sum=0.; #pragma omp parallel for reduction(+:sum) for(uint64_t u=umin; u<umax; u++) sum+=1./u/u; printf("%e\n", sum); } I was surprised to find that the scaling is highly nonlinear. It takes about 2.9s for the code to run with 48 threads, 3.1s with 36 threads, 3.7s with 24 threads, 4.9s with 12 threads, and 57s for the code to run with 1 thread. Unfortunately I have to say that there is one process running on the computer using 100% of one core, so that might be affecting it. It's not my process, so I can't end it to test the difference, but somehow I doubt that's making the difference between a 19~20x speedup and the ideal 48x speedup. To make sure it wasn't an OpenMP issue, I ran two copies of the program at the same time with 24 threads each (one with umin=1, umax=5000000000, and the other with umin=5000000000, umax=10000000000). In that case both copies of the program finish after 2.9s, so it's exactly the same as running 48 threads with a single instance of the program. What's preventing linear scaling with this simple program?

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  • Invoking a function (main()) from a binary file in C

    - by Dhara Darji
    I have simple c program like, my_bin.c: #include <stdio.h> int main() { printf("Success!\n"); return 0; } I compile it with gcc and got executable: my_bin. Now I want to invoke main (or run this my_bin) using another C program. That I did with mmap and function pointer like this: #include <stdio.h> #include <fcntl.h> #include <sys/mman.h> int main() { void (*fun)(); int fd; int *map; fd = open("./my_bin", O_RDONLY); map = mmap(0, 8378, PROT_READ, MAP_SHARED, fd, 0); fun = map; fun(); return 0; } PS: I went through some tutorial, for how to read binary file and execute. But this gives Seg fault, any help appreciated! Thanks!

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  • How to configure and run a fastcgi application using Lighthttpd...

    - by Airy
    Hi, i've installed Lighthttpd for windows and i'd created a simple program in c++ which uses fastcgi libraries. i'll post the code here... #include "fcgi_stdio.h" #include <stdlib.h> int count; void initialize(void) { count=0; } void main(void) { initialize(); while (FCGI_Accept() >= 0) { printf("Content-type: text/html\r\n" "\r\n" "<title>FastCGI Hello! (C, fcgi_stdio library)</title>" "<h1>FastCGI Hello! (C, fcgi_stdio library)</h1>" "Request number %d running on host <i>%s</i>\n", ++count, getenv("SERVER_HOSTNAME")); } } I've spawned the fastcgi application in lighthttpd using the below configuration in lightttpd-inc.conf fastcgi.server = ( ".exe" => ( "" => ( "bin-path" => "D:\tinycgi.exe", "port" => 8080, "min-procs" => 1, "max-procs" => 1 ) ) ) while sending a request using the browser the server is responding with this message in the console 2009-02-18 16:08:34: (mod_fastcgi.c.2494) unexpected end-of-file (perhaps the fa stcgi process died): pid: 0 socket: tcp:localhost:8080 2009-02-18 16:08:34: (mod_fastcgi.c.3325) response not received, request sent: 1 024 on socket: tcp:localhost:8080 for /new/tinycgi.exe , closing connection I think the fastcgi application is not spawned correctly. Thank you, Varun

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  • is it possible to write a program which prints its own source code utilizing a "sequence-generating-

    - by guest
    is it possible to write a program which prints its own source code utilizing a "sequence-generating-function"? what i call a sequence-generating-function is simply a function which returns a value out of a specific interval (i.e. printable ascii-charecters (32-126)). the point now is, that this generated sequence should be the programs own source-code. as you see, implementing a function which returns an arbitrary sequence is really trivial, but since the returned sequence must contain the implementation of the function itself it is a highly non-trivial task. this is how such a program (and its corresponding output) could look like #include <stdio.h> int fun(int x) { ins1; ins2; ins3; . . . return y; } int main(void) { int i; for ( i=0; i<size of the program; i++ ) { printf("%c", fun(i)); } return 0; } i personally think it is not possible, but since i don't know very much about the underlying matter i posted my thoughts here. i'm really looking forward to hear some opinions!

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  • Output problem in mysql query in MFC program

    - by D.Gaughan
    Im currently working on a small MFC program that outputs data from a mysql database. I can get output when im using an sql statement that does not contain any variable eg. select album from Artists; but when i try to use a variable the program compiles but i get no output eg. mysql_perform_query(conn,select album from Artists where artists = '"+m_search_edit"'") Here is the function for mysql_perform_query: MYSQL_RES* mysql_perform_query(MYSQL *conn, const char* query) { // send the query to the database if (mysql_query(conn, query)) { // printf("MySQL query error : %s\n", mysql_error(conn)); // exit(1); } return mysql_use_result(conn); } And here is the code block for outputting the data: struct connection_details mysqlD; mysqlD.server = "www.freesqldatabase.com"; // where the mysql database is mysqlD.user = "**********"; // the root user of mysql mysqlD.password = "***********"; // the password of the root user in mysql mysqlD.database = "***************"; // the databse to pick // connect to the mysql database conn = mysql_connection_setup(mysqlD); CStringA query; query.Format("select album from Artists where artist = '%s'", CT2CA(m_search_edit)); res = mysql_perform_query(conn, query); //res = mysql_perform_query (conn, "select distinct artist from Artists"); while((row = mysql_fetch_row(res)) != NULL){ CString str; UpdateData(); str = ("%s\n", row[0]); UpdateData(FALSE); m_list_control.AddString(str); } The m_search_edit variable is the variable for an edit box. I am using Visual Studio 2008 with one copy of this program unicode and one nonunicode, I also have a version built with VC++ 6. Any tips on how I can get output from the databse using the m_search_edit variable??

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  • C: incompatible types in assignment

    - by The.Anti.9
    I'm writing a program to check to see if a port is open in C. One line in particular copies one of the arguments to a char array. However, when I try to compile, it says: error: incompatible types in assignment Heres the code. The error is on the assignment of addr #include <sys/socket.h> #include <sys/time.h> #include <sys/types.h> #include <arpa/inet.h> #include <netinet/in.h> #include <errno.h> #include <fcntl.h> #include <stdio.h> #include <netdb.h> #include <stdlib.h> #include <string.h> #include <unistd.h> int main(int argc, char **argv) { u_short port; /* user specified port number */ char addr[1023]; /* will be a copy of the address entered by u */ struct sockaddr_in address; /* the libc network address data structure */ short int sock = -1; /* file descriptor for the network socket */ port = atoi(argv[1]); addr = strncpy(addr, argv[2], 1023); bzero((char *)&address, sizeof(address)); /* init addr struct */ address.sin_addr.s_addr = inet_addr(addr); /* assign the address */ address.sin_port = htons(port); /* translate int2port num */ sock = socket(AF_INET, SOCK_STREAM, 0); if (connect(sock,(struct sockaddr *)&address,sizeof(address)) == 0) { printf("%i is open\n", port); } if (errno == 113) { fprintf(stderr, "Port not open!\n"); } close(sock); return 0; } I'm new to C, so I'm not sure why it would do this.

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  • C: socket connection timeout

    - by The.Anti.9
    I have a simple program to check if a port is open, but I want to shorten the timeout length on the socket connection because the default is far too long. I'm not sure how to do this though. Here's the code: #include <sys/socket.h> #include <sys/time.h> #include <sys/types.h> #include <arpa/inet.h> #include <netinet/in.h> #include <errno.h> #include <fcntl.h> #include <stdio.h> #include <netdb.h> #include <stdlib.h> #include <string.h> #include <unistd.h> int main(int argc, char **argv) { u_short port; /* user specified port number */ char addr[1023]; /* will be a copy of the address entered by u */ struct sockaddr_in address; /* the libc network address data structure */ short int sock = -1; /* file descriptor for the network socket */ if (argc != 3) { fprintf(stderr, "Usage %s <port_num> <address>", argv[0]); return EXIT_FAILURE; } address.sin_addr.s_addr = inet_addr(argv[2]); /* assign the address */ address.sin_port = htons(atoi(argv[2])); /* translate int2port num */ sock = socket(AF_INET, SOCK_STREAM, 0); if (connect(sock,(struct sockaddr *)&address,sizeof(address)) == 0) { printf("%i is open\n", port); } close(sock); return 0; }

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  • Makefile; mirroring a growing tree through a process

    - by Martineau
    I would like to periodically mirror a growing tree, say, from $in to $out, doing a process in between (saving the only file header). As; #!/bin/bash in=./segd out=./db for f in `find $in -name "*.segd"`;do # Deduct output (dir + name) d=`dirname $f|perl -pe 's!'$in'!'$out'!'` n=`basename $f|perl -pe 's!$!_hdr!'` if [ ! -e $d/$n ]; then [ ! -d $d ] && mkdir -p $d; printf "From %s now build %s\n" $f "$d/$n" # Do something, whathever. For example e.g; dd if=$f bs=32 count=1 conv=swab 2>/dev/null|od -x > $d/$n fi done That is about fair. However; to be more robust, for a better synchronization (say if a source file did change or whatever), I would like to use a Makefile, as in; HDR := $(patsubst ./segd/%.segd,./db/%.segd_hdr,$(wildcard ./segd/*.segd)) all: ${HDR} db/%.segd_hdr: ./segd/%.segd echo "Doing" dd if=$< bs=32 count=1 conv=swab 2>/dev/null|od -x > $@ My problem; I cannot code this Makefile to "dive" more deeply within the source ./segd tree. How can we do it and is there a way ? Many thanks for your kind recommendations. PS: The idea will be to later rsync the (smaller) destination tree over a sat connection.

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  • C - dns query to structure

    - by Bibo
    I have these structures: typedef struct dnsQuery { char header[12]; struct dnsQuerySection *querySection; } TdnsQuery; typedef struct dnsQuerySection { unsigned char *name; struct dnsQueryQuestion *question; } TdnsQuerySection; typedef struct dnsQueryQuestion { unsigned short qtype; unsigned short qclass; } TdnsQueryQuestion; and I have dns query in byte array from recvfrom. I am trying to get structure from byte array like this: TdnsQuery* dnsQuery = (TdnsQuery*)buf; When I tried to access qtype like this: printf("%u", dnsQuery->querySection->question.qtype); I get seg fault 11. Can someone help me with these structures? What´s wrong with them? I tried to add structure: typedef struct udpPacket { char header[8]; structr dnsQuery query; } and mapped this structure from byte array but it didn´t help. Can someone help me with these structures? How they should look like for dns query with udp protocol?

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  • Go and a bad prime number algorithm

    - by anonymous
    I wrote this prime number sieving algorithm and it doesn't run properly. I can't find the error in the algorithm itself. Could someone help me? This is what it's supposed to print: [2 3 5 7 11 13 17 19 23 29] Versus what it actually prints: [3 5 7 11 13 17 19 23 25 29] . package main import "fmt" func main() { var primes = sieve(makeNumbers(29)) fmt.Printf("%d\n", primes); } func makeNumbers(n int) []int { var numbers = make([]int, n - 1) for i := 0; i < len(numbers); i++ { numbers[i] = i + 2 } return numbers } func sieve(numbers []int) []int { var numCopy = numbers var max = numbers[len(numbers)-1] var sievedNumbers = make([]int, 0) for i := 0; numCopy[i]*numCopy[i] <= max; i++ { for j := i; j < len(numCopy); j++ { if numCopy[j] % numCopy[i] != 0 || j == i { sievedNumbers = append(sievedNumbers, numCopy[j]) } } numCopy = sievedNumbers sievedNumbers = make([]int, 0) } return numCopy }

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  • Assigning a value to a variable gets stored in the wrong spot?

    - by scribbloid
    Hello, I'm relatively new to C, and this is baffling me right now. It's part of a much larger program, but I've written this little program to depict the problem I'm having. #include <stdio.h> int main() { signed int tcodes[3][1]; tcodes[0][0] = 0; tcodes[0][1] = 1000; tcodes[1][0] = 1000; tcodes[1][1] = 0; tcodes[2][0] = 0; tcodes[2][1] = 1000; tcodes[3][0] = 1000; tcodes[3][1] = 0; int x, y, c; for(c = 0; c <= 3; c++) { printf("%d %d %d\r\n", c, tcodes[c][0], tcodes[c][1]); x = 20; y = 30; } } I'd expect this program to output: 0 0 1000 1 1000 0 2 0 1000 3 1000 0 But instead, I get: 0 0 1000 1 1000 0 2 0 20 3 20 30 It does this for any number assigned to x and y. For some reason x and y are overriding parts of the array in memory. Can someone explain what's going on? Thanks!

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  • BASIC Menu-driven program repeates twice after successful completion of first task.

    - by Zazu
    Hello, Im using Plato3 to write C programs. Im creating a menu-driven program but want to test out the basic concept of getting it to work #include<stdio.h> #include<ctype.h> int function1(); main(){ char s; do{ puts("\n choose the following"); puts("(P)rint\n"); puts("(Q)uit\n"); scanf("%c",&s); s=toupper(s); switch (s){ case 'P' : function1(); break; case 'Q' : return -1; break; } }while (function1()==0); } int function1(){ printf("Hello World"); return 0; } The problem is that once function1() returns the value 0, the whole program is echoed ... why ? Example : Running the program gives this : Hello WorldHellow World choose the following (P)rint (Q)uit Hello World choose the following (P)rint (Q)uit -- Any idea why ? Please help, thanks !!!!

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  • Having a problem inserting into database

    - by neo skosana
    I have a stored procedure: CREATE PROCEDURE busi_reg(IN instruc VARCHAR(10), IN tble VARCHAR(20), IN busName VARCHAR(50), IN busCateg VARCHAR(100), IN busType VARCHAR(50), IN phne VARCHAR(20), IN addrs VARCHAR(200), IN cty VARCHAR(50), IN prvnce VARCHAR(50), IN pstCde VARCHAR(10), IN nm VARCHAR(20), IN surname VARCHAR(20), IN eml VARCHAR(50), IN pswd VARCHAR(20), IN srce VARCHAR(50), IN refr VARCHAR(50), IN sess VARCHAR(50)) BEGIN INSERT INTO b_register SET business_name = busName, business_category = busCateg, business_type = busType, phone = phne, address = addrs, city = cty, province = prvnce, postal_code = pstCde, firstname = nm, lastname = surname, email = eml, password = pswd, source = srce, ref_no = refr; END; This is my php script: $busName = $_POST['bus_name']; $busCateg = $_POST['bus_cat']; $busType = $_POST['bus_type']; $phne = $_POST['phone']; $addrs = $_POST['address']; $cty = $_POST['city']; $prvnce = $_POST['province']; $pstCde = $_POST['postCode']; $nm = $_POST['name']; $surname = $_POST['lname']; $eml = $_POST['email']; $srce = $_POST['source']; $ref = $_POST['ref_no']; $result2 = $db->query("CALL busi_reg('$instruc', '$tble', '$busName', '$busCateg', '$busType', '$phne', '$addrs', '$cty', '$prvnce', '$pstCde', '$nm', '$surname', '$eml', '$pswd', '$srce', '$refr', '')"); if($result) { echo "Data has been saved"; } else { printf("Error: %s\n",$db->error); } Now the error that I get: Commands out of sync; you can't run this command now

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  • Sending data in a GTK Callback

    - by snostorm
    How can I send data through a GTK callback? I've Googled, and with the information I found created this: #include <gtk/gtk.h> #include <stdio.h> void button_clicked( GtkWidget *widget, GdkEvent *event, gchar *data); int main( int argc, char *argv[]){ GtkWidget *window; GtkWidget *button; gtk_init (&argc, &argv); window = gtk_window_new(GTK_WINDOW_TOPLEVEL); button = gtk_button_new_with_label("Go!"); gtk_container_add(GTK_CONTAINER(window), button); g_signal_connect_swapped(G_OBJECT(window), "destroy", G_CALLBACK(gtk_main_quit), NULL); g_signal_connect(G_OBJECT(button), "clicked", G_CALLBACK(button_clicked),"test" ); gtk_widget_show(window); gtk_widget_show(button); gtk_main(); return 0; } void button_clicked( GtkWidget *widget, GdkEvent *event, gchar *data){ printf("%s \n", (gchar *) data); return; } But it just Segfaults when I press the button. What is the right way to do this?

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  • creating QT gui using a thread in c++?

    - by rashid
    I am trying to create this QT gui using a thread but no luck. Below is my code. Problem is gui never shows up. /*INCLUDES HERE... .... */ using namespace std; struct mainStruct { int s_argc;<br> char ** s_argv; }; typedef struct mainStruct mas; void *guifunc(void * arg); int main(int argc, char * argv[]) { mas m;<br> m.s_argc = argc;<br> m.s_argv = argv;<br> pthread_t threadGUI; //start a new thread for gui int result = pthread_create(&threadGUI, NULL, guifunc, (void *) &m); if (result) {<br> printf("Error creating gui thread"); exit(0); } return 0; } void *guifunc(void * arg) { mas m = *(mas *)arg; QApplication app(m.s_argc,m.s_argv); //object instantiation<br> guiClass *gui = new guiClass(); //show gui<br> gui->show(); app.exec(); <br> }

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  • Looking for Go equivalent of scanf.

    - by Stephen Hsu
    I'm looking for the Go equivalent of scanf(). I tried with following code: 1 package main 2 3 import ( 4 "scanner" 5 "os" 6 "fmt" 7 ) 8 9 func main() { 10 var s scanner.Scanner 11 s.Init(os.Stdin) 12 s.Mode = scanner.ScanInts 13 tok := s.Scan() 14 for tok != scanner.EOF { 15 fmt.Printf("%d ", tok) 16 tok = s.Scan() 17 } 18 fmt.Println() 19 } I run it with input from a text with a line of integers. But it always output -3 -3 ... And how to scan a line composed of a string and some integers? Changing the mode whenever encounter a new data type? The Package documentation: Package scanner A general-purpose scanner for UTF-8 encoded text. But it seems that the scanner is not for general use. Updated code: func main() { n := scanf() fmt.Println(n) fmt.Println(len(n)) } func scanf() []int { nums := new(vector.IntVector) reader := bufio.NewReader(os.Stdin) str, err := reader.ReadString('\n') for err != os.EOF { fields := strings.Fields(str) for _, f := range fields { i, _ := strconv.Atoi(f) nums.Push(i) } str, err = reader.ReadString('\n') } r := make([]int, nums.Len()) for i := 0; i < nums.Len(); i++ { r[i] = nums.At(i) } return r }

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  • c++ tables of unions and structures

    - by newbDeveloper
    I was told to write a program, that creates a union and structure, then creates two-element arrays of unions and structures and fills their fields. I have created a union and a structure, but how to fill their fields in arrays ? #include <iostream> #include <stdlib.h> #include <stdio.h> using namespace std; union complex; union complex{ int i1; long double ld1; } u; struct Person { char* name; int age; bool sex; void show(){ printf("name %s, age %2.0d, sex %1d\n", name , age, sex); }; } person; int main(void) { Person *o = new Person[2]; complex *un = new complex[2]; un[0]->i1=i; system("pause"); return 0; } I've tried un[0]-i1=i; but it's not the proper way to do this.

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  • char[] and char* compatibility?

    - by Aerovistae
    In essence, will this code work? And before you say "Run it and see!", I just realized my cygwin didn't come with gcc and it's currently 40 minutes away from completing reinstallation. That being said: char* words[1000]; for(int i = 0; i<1000; i++) words[i] = NULL; char buffer[ 1024 ]; //omit code that places "ADD splash\0" into the buffer if(strncmp (buffer, "ADD ", 4){ char* temp = buffer + 4; printf("Adding: %s", temp); int i = 0; while(words[i] != NULL) i++; words[i] = temp; } I'm mostly uncertain about the line char* temp = buffer + 4, and also whether I can assign words[i] in the manner that I am. Am I going to get type errors when I eventually try to compile this in 40 minutes? Also-- if this works, why don't I need to use malloc() on each element of words[]? Why can I say words[i] = temp, instead of needing to allocate memory for words[i] the length of temp?

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  • creating a QT gui using a thread in c++?

    - by rashid
    I am trying to create this QT gui using a thread but no luck. Below is my code. Problem is gui never shows up. But if i put QApplication app(m.s_argc,m.s_argv); //object instantiation guiClass *gui = new guiClass(); //show gui gui-show(); app.exec(); in main() then it works. /*INCLUDES HERE... .... */ using namespace std; struct mainStruct { int s_argc; char ** s_argv; }; typedef struct mainStruct mas; void *guifunc(void * arg); int main(int argc, char * argv[]) { mas m; m.s_argc = argc; m.s_argv = argv; pthread_t threadGUI; //start a new thread for gui int result = pthread_create(&threadGUI, NULL, guifunc, (void *) &m); if (result) { printf("Error creating gui thread"); exit(0); } return 0; } void *guifunc(void * arg) { mas m = *(mas *)arg; QApplication app(m.s_argc,m.s_argv); //object instantiation guiClass *gui = new guiClass(); //show gui gui-show(); app.exec(); }

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  • GetIpAddrTable() leaks memory. How to resolve that?

    - by Stabledog
    On my Windows 7 box, this simple program causes the memory use of the application to creep up continuously, with no upper bound. I've stripped out everything non-essential, and it seems clear that the culprit is the Microsoft Iphlpapi function "GetIpAddrTable()". On each call, it leaks some memory. In a loop (e.g. checking for changes to the network interface list), it is unsustainable. There seems to be no async notification API which could do this job, so now I'm faced with possibly having to isolate this logic into a separate process and recycle the process periodically -- an ugly solution. Any ideas? // IphlpLeak.cpp - demonstrates that GetIpAddrTable leaks memory internally: run this and watch // the memory use of the app climb up continuously with no upper bound. #include <stdio.h> #include <windows.h> #include <assert.h> #include <Iphlpapi.h> #pragma comment(lib,"Iphlpapi.lib") void testLeak() { static unsigned char buf[16384]; DWORD dwSize(sizeof(buf)); if (GetIpAddrTable((PMIB_IPADDRTABLE)buf, &dwSize, false) == ERROR_INSUFFICIENT_BUFFER) { assert(0); // we never hit this branch. return; } } int main(int argc, char* argv[]) { for ( int i = 0; true; i++ ) { testLeak(); printf("i=%d\n",i); Sleep(1000); } return 0; }

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  • Capabilities & Linux & Java

    - by Marek Jelen
    Hi, I am experimenting with linux capabilities for java application ... I do not want to add capabilities to interpreter (JVM), so I tried to write simple wrapper (with debugging information printed to stdout): #include <stdio.h> #include <stdlib.h> #include <sys/capability.h> #include <unistd.h> int main(int argc, char *argv[]){ cap_t cap = cap_get_proc(); if (!cap) { perror("cap_get_proc"); exit(1); } printf("%s: running with caps %s\n", argv[0], cap_to_text(cap, NULL)); return execlp("/usr/bin/java", "-server", "-jar", "project.jar", (char *)NULL); } This way, I can se that the capability is set for this execucatable: ./runner: running with caps = cap_net_bind_service+p And getcap shows runner = cap_net_bind_service+ip I have the capability set to be inheritable, so there should be no problem. However java still don't want to bind to privileged ports :-( I am getting this error: sun/nio/ch/Net.java:-2:in `bind': java.net.SocketException: Permission denied (NativeException) Can someone help me to resolve this? Thanks in advance

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  • Prob comparing pointers and integer in C

    - by Dimitri
    Hi I have a problem with this code. When i am using this function I have no warnings. : void handler(int sig){ switch(sig) { case SIGINT : { click++; fprintf(stdout,"SIGINT recu\n"); if( click == N){ exit(0); } } case SIGALRM : fprintf(stdout,"SIGALRM received\n"); exit(0); case SIGTERM: fprintf(stdout,"SIGTERM received\n"); exit(0); } } But when i rewrite the function with this new version, I have a " comparison between pointer and integer" warning on the if statement: void handler( int sig){ printf("Signal recu\n"); if( signal == SIGINT){ click++; fprintf(stdout,"SIGINT received; Click = %d\n",click); if(click == N){ fprintf(stdout,"Exiting with SIGINT\n"); exit(0); } } else if(signal == SIGALRM){ fprintf(stdout,"SIGALRM received\n"); exit(0); } else if(signal == SIGTERM){ fprintf(stdout,"SIGTERM received\n"); exit(0); } Can someone tell me where is the prob?

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  • SSE (SIMD extensions) support in gcc

    - by goldenmean
    Hi, I see a code as below: include "stdio.h" #define VECTOR_SIZE 4 typedef float v4sf __attribute__ ((vector_size(sizeof(float)*VECTOR_SIZE))); // vector of four single floats typedef union f4vector { v4sf v; float f[VECTOR_SIZE]; } f4vector; void print_vector (f4vector *v) { printf("%f,%f,%f,%f\n", v->f[0], v->f[1], v->f[2], v->f[3]); } int main() { union f4vector a, b, c; a.v = (v4sf){1.2, 2.3, 3.4, 4.5}; b.v = (v4sf){5., 6., 7., 8.}; c.v = a.v + b.v; print_vector(&a); print_vector(&b); print_vector(&c); } This code builds fine and works expectedly using gcc (it's inbuild SSE / MMX extensions and vector data types. this code is doing a SIMD vector addition using 4 single floats. I want to understand in detail what does each keyword/function call on this typedef line means and does: typedef float v4sf __attribute__ ((vector_size(sizeof(float)*VECTOR_SIZE))); What is the vector_size() function return; What is the __attribute__ keyword for Here is the float data type being type defined to vfsf type? I understand the rest part. thanks, -AD

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  • C: Fifo between threads, writing and reading strings

    - by Yonatan
    Hello once more dear internet, I writing a small program that among other things, writes a log file of commands received. to do that, I want to use a thread that all it should do is just attempt to read from a pipe, while the main thread will write into that pipe whenever it should. Since i don't know the length of each string command, i thought about writing and reading the pointer to the char buf[MAX_MESSAGE_LEN]. Since what i've tried so far doesn't work, i'll post my best effort :P char str[] = "hello log thread 123456789 10 11 12 13 14 15 16 17 18 19\n"; if (pipe(pipe_fd) != 0) return -1; pthread_t log_thread; pthread_create(&log_thread,NULL, log_thread_start, argv[2]); success_write = 0; do { write(pipe_fd[1],(void*)&str,sizeof(char*)); } while (success_write < sizeof(char*)); and the thread does this: char buffer[MAX_MSGLEN]; int success_read; success_read = 0; //while(1) { do { success_read += read(pipe_fd[0],(void*)&buffer, sizeof(char*)); } while (success_read < sizeof(char*)); //} printf("%s",buffer); (Sorry if this doesn't indent, i can't seem to figure out this editor...) oh, and pipe_fd[2] is a global parameter. So, any help with this, either by the way i thought of, or another way i could read strings without knowing the length, would be much appreciated. On a side note, i'm working on Eclipse IDE C/C++, version 1.2.1 and i can't seem to set up the compiler so it will link the pthread library to my project. I've resorted to writing my own Makefile to make it (pun intended :P) work. Anyone knows what to do ? i've looked online, but all i find are solutions that are probably good on an older version because the tabs and option keys are different. Anyways, Thanks a bunch internet ! Yonatan

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  • Find Pythagorean triplet for which a + b + c = 1000

    - by Rahul
    A Pythagorean triplet is a set of three natural numbers, a < b < c, for which, a^(2) + b^(2) = c^(2) For example, 3^(2) + 4^(2) = 9 + 16 = 25 = 5^(2). There exists exactly one Pythagorean triplet for which a + b + c = 1000. Find the product abc. Source: http://projecteuler.net/index.php?section=problems&id=9 I tried but didn't know where my code went wrong. Here's my code in C: #include <stdio.h> void main() { int a, b, c; for (a = 0; a<=1000; a++) { for (b = 0; b<=1000; b++) { for (c = 0; c<=1000; c++) { if (((a^(2) + b^(2) == c^(2)) && ((a+b+c) ==1000))) printf("a=%d, b=%d, c=%d",a,b,c); } } } return 0; }

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