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• pinpointing "conditional jump or move depends on uninitialized value(s)" valgrind message

  - by kamziro

  So I've been getting some mysterious uninitialized values message from valgrind and it's been quite the mystery as of where the bad value originated from. Seems that valgrind shows the place where the unitialised value ends up being used, but not the origin of the uninitialised value. ==11366== Conditional jump or move depends on uninitialised value(s) ==11366== at 0x43CAE4F: __printf_fp (in /lib/tls/i686/cmov/libc-2.7.so) ==11366== by 0x43C6563: vfprintf (in /lib/tls/i686/cmov/libc-2.7.so) ==11366== by 0x43EAC03: vsnprintf (in /lib/tls/i686/cmov/libc-2.7.so) ==11366== by 0x42D475B: (within /usr/lib/libstdc++.so.6.0.9) ==11366== by 0x42E2C9B: std::ostreambuf_iterator<char, std::char_traits<char> > std::num_put<char, std::ostreambuf_iterator<char, std::char_traits<char> > >::_M_insert_float<double>(std::ostreambuf_iterator<char, std::char_traits<char> >, std::ios_base&, char, char, double) const (in /usr/lib/libstdc++.so.6.0.9) ==11366== by 0x42E31B4: std::num_put<char, std::ostreambuf_iterator<char, std::char_traits<char> > >::do_put(std::ostreambuf_iterator<char, std::char_traits<char> >, std::ios_base&, char, double) const (in /usr/lib/libstdc++.so.6.0.9) ==11366== by 0x42EE56F: std::ostream& std::ostream::_M_insert<double>(double) (in /usr/lib/libstdc++.so.6.0.9) ==11366== by 0x81109ED: Snake::SnakeBody::syncBodyPos() (ostream:221) ==11366== by 0x810B9F1: Snake::Snake::update() (snake.cpp:257) ==11366== by 0x81113C1: SnakeApp::updateState() (snakeapp.cpp:224) ==11366== by 0x8120351: RoenGL::updateState() (roengl.cpp:1180) ==11366== by 0x81E87D9: Roensachs::update() (rs.cpp:321) As can be seen, it gets quite cryptic.. especially because when it's saying by Class::MethodX, it sometimes points straight to ostream etc. Perhaps this is due to optimization? ==11366== by 0x81109ED: Snake::SnakeBody::syncBodyPos() (ostream:221) Just like that. Is there something I'm missing? What is the best way to catch bad values without having to resort to super-long printf detective work?

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• Error while compiling Hello world program for CUDA

  - by footy

  I am using Ubuntu 12.10 and have sucessfully installed CUDA 5.0 and its sample kits too. I have also run sudo apt-get install nvidia-cuda-toolkit Below is my hello world program for CUDA: #include <stdio.h> /* Core input/output operations */ #include <stdlib.h> /* Conversions, random numbers, memory allocation, etc. */ #include <math.h> /* Common mathematical functions */ #include <time.h> /* Converting between various date/time formats */ #include <cuda.h> /* CUDA related stuff */ __global__ void kernel(void) { } /* MAIN PROGRAM BEGINS */ int main(void) { /* Dg = 1; Db = 1; Ns = 0; S = 0 */ kernel<<<1,1>>>(); /* PRINT 'HELLO, WORLD!' TO THE SCREEN */ printf("\n Hello, World!\n\n"); /* INDICATE THE TERMINATION OF THE PROGRAM */ return 0; } /* MAIN PROGRAM ENDS */ The following error occurs when I compile it with nvcc -g hello_world_cuda.cu -o hello_world_cuda.x /tmp/tmpxft_000033f1_00000000-13_hello_world_cuda.o: In function `main': /home/adarshakb/Documents/hello_world_cuda.cu:16: undefined reference to `cudaConfigureCall' /tmp/tmpxft_000033f1_00000000-13_hello_world_cuda.o: In function `__cudaUnregisterBinaryUtil': /usr/include/crt/host_runtime.h:172: undefined reference to `__cudaUnregisterFatBinary' /tmp/tmpxft_000033f1_00000000-13_hello_world_cuda.o: In function `__sti____cudaRegisterAll_51_tmpxft_000033f1_00000000_4_hello_world_cuda_cpp1_ii_b81a68a1': /tmp/tmpxft_000033f1_00000000-1_hello_world_cuda.cudafe1.stub.c:1: undefined reference to `__cudaRegisterFatBinary' /tmp/tmpxft_000033f1_00000000-1_hello_world_cuda.cudafe1.stub.c:1: undefined reference to `__cudaRegisterFunction' /tmp/tmpxft_000033f1_00000000-13_hello_world_cuda.o: In function `cudaError cudaLaunch<char>(char*)': /usr/lib/nvidia-cuda-toolkit/include/cuda_runtime.h:958: undefined reference to `cudaLaunch' collect2: ld returned 1 exit status I am also making sure that I use gcc and g++ version 4.4 ( As 4.7 there is some problem with CUDA)

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• Problem when reading input in C

  - by gcx

  I've made a Linked List. Its elements keep both previous and next items' address. It gets commands from an input file. It detects the command and uses the following statement as a parameter. (text: add_to_front john - means: add_to_front(john)) Code: http://pastebin.com/KcAm1y3L When I try to give the commands from an input file it gives me same output over and over. However, if I write inputs in main() manually, it works. For ex input file: add_to_front john add_to_back jane add_to_back jane print (unfortunately) the output is: >add_to_front john >add_to_back jane >add_to_back jane >print jane jane jane Although, if I write add_to_front(john); add_to_back(jane); add_to_back(jane); print(); instead of this command check: while (scanf("%s",command)!=EOF) { if (strcmp(command,"add_to_front")==0) { gets(parameter); add_to_front(parameter); } else if (strcmp(command,"add_to_back")==0) { gets(parameter); add_to_back(parameter); } else if (strcmp(command,"remove_from_back")==0) remove_from_back(parameter); ... printf(" HUH?\n"); } } in main() it gives the correct output. I know it's a lot to ask but this thing is bothering me for 2 days. What do you think i'm doing wrong?

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• What's wrong with debugging in Eclipse on Android?

  - by Sebastian Dwornik

  I've obviously been spoiled by Visual Studio, because although I'm just learning Android and the Eclipse environment, debugging apps in Eclipse is becoming a serious detriment to further development. For example, Eclipse will compile this divide by zero just fine: public class Lesson2Main extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate (savedInstanceState); int i = 1 / 0; TextView tv = new TextView (this); tv.setText ("Hello, Android!"); setContentView (tv); } } And then, when it executes it under the debugger, I will get a full screen of useless debug info, non of which actually points me to the specific line containing the error. The stackTrace is null within the exception ('e') info tree, and it simply states a message stating 'ArithmeticException'. (that's nice, how about you point me in the direction of where you found it!?) I've looked all over the screen and am baffled that this IDE can't get this right. Does developing with Eclipse resort everyone back to 1991 with printf() like logging at every interval then to track down bugs? Seriously. Is there a configuration or plug-in that I'm missing to help with this? I haven't tested this case with XCode, but if the iPhone dev. IDE handles this more like Visual Studio, then no wonder the Android marketplace has so few apps. I'm excited about Android, but it seems that Eclipse is getting in the way.

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• What does O(log n) mean exactly?

  - by Andreas Grech

  I am currently learning about Big O Notation running times and amortized times. I understand the notion of O(n) linear time, meaning that the size of the input affects the growth of the algorithm proportionally...and the same goes for, for example, quadratic time O(n2) etc..even algorithms, such as permutation generators, with O(n!) times, that grow by factorials. For example, the following function is O(n) because the algorithm grows in proportion to its input n: f(int n) { int i; for (i = 0; i < n; ++i) printf("%d", i); } Similarly, if there was a nested loop, the time would be O(n2). But what exactly is O(log n)? For example, what does it mean to say that the height of a complete binary tree is O(log n)? I do know (maybe not in great detail) what Logarithm is, in the sense that: log10 100 = 2, but I cannot understand how to identify a function with a logarithmic time.

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• fgets in c doesn't return a portion of an string

  - by Marc

  Hi! I'm totally new in C, and I'm trying to do a little application that searches a string into a file, my problem is that I need to open a big file (more than 1GB) with just one line inside and fgets return me the entire file (I'm doing test with a 10KB file). actually this is my code: #include <stdio.h> #include <string.h> int main(int argc, char *argv[]) { char *search = argv[argc-1]; int retro = strlen(search); int pun = 0; int sortida; int limit = 10; char ara[20]; FILE *fp; if ((fp = fopen ("SEARCHFILE", "r")) == NULL){ sortida = -1; exit (1); } while(!feof(fp)){ if (fgets(ara, 20, fp) == NULL){ break; } //this must be a 20 bytes line, but it gets the entyre 10Kb file printf("%s",ara); } sortida = 1; if(fclose(fp) != 0){ sortida = -2; exit (1); } return 0; } What can I do to find an string into a file? I'v tried with GREP but it don't helps, because it returns the position:ENTIRE_STRING. I'm open to ideas. Thanks in advance!

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• Unresolved external symbol - MySQL API C++

  - by Zack_074

  Hey I've had nonstop problems with SQL. I'm trying to get some experience because I know it's a vital part of the industry. I got it working with C#, but now I'm working on connecting to a database in c++. I have the project properly linked and what not. Here's my code and the errors I'm getting. #include "stdafx.h" #include <mysql.h> #include <iostream> MYSQL mysql; MYSQL_RES result; using namespace std; int _tmain(int argc, _TCHAR* argv[]) { mysql_init(&mysql); if(!mysql_real_connect(&mysql, "localhost", "root", "angel552002", "MyDatabse", 0, NULL, 0)) { printf("Failed to connect"); } return 0; } and the errors: Error 1 error LNK2001: unresolved external symbol _mysql_real_connect@32 c:\Users\Zack-074\documents\visual studio 2010\Projects\MySql\MySql\MySql.obj Error 2 error LNK2001: unresolved external symbol _mysql_init@4 c:\Users\Zack-074\documents\visual studio 2010\Projects\MySql\MySql\MySql.obj Error 3 error LNK1120: 2 unresolved externals c:\users\zack-074\documents\visual studio 2010\Projects\MySql\Debug\MySql.exe 1 I really appreciate the help.

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• C & MinGW: Hello World gives me the error "programm too big to fit in memory"

  - by user1692088

  I'm new here. Here's my problem: I installed MinGW on my Windows 7 Home Premium 32-bit Netbook with Intel Atom CPU N550, 1.50GHz and 2GB RAM. Now I made a file named hello.h and tried to compile it via CMD with the following command: "gcc c:\workspace\c\helloworld\hello.h -o out.exe" It compiles with no error, but when I try to run out.exe, it gives me following error: "program too big to fit in memory" Things I have checked: I have added "C:\MinGW\bin" to the Windows PATH Variable I have googled for about one hour, but ever since I'm a newbie, I can't really figure out what the problem is. I have compiled the same code on my 64-bit machine, compiles perfectly, but cannot be run due to 64-bit <- 16-bit problematic. I'd really appreciate, if someone could figure out, what the problem is. Btw, here's my hello.h: #include <stdio.h> int main(void){ printf("Hello, World\n"); } ... That's it. Thanks for your replies. Cheers, Boris

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• Linked List Sorting with Strings In C

  - by user308583

  I have a struct, with a Name and a single Node called nextName It's a Singly Linked list, and my task is to create the list, based on alphabetical order of the strings. So iff i enter Joe Zolt and Arthur i should get my list structured as Joe Than Joe Zolt Than Arthur Joe Zolt I'm having trouble implementing the correct Algorithm, which would put the pointers in the right order. This is What I have as of Now. Temp would be the name the user just entered and is trying to put into the list, namebox is just a copy of my root, being the whole list if(temp != NULL) { struct node* namebox = root; while (namebox!=NULL && (strcmp((namebox)->name,temp->name) <= 0)) { namebox = namebox->nextName; printf("here"); } temp->nextName = namebox; namebox = temp; root = namebox; This Works right now, if i enter names like CCC BBB than AAA I Get Back AAA BBB CCC when i print But if i put AAA BBB CCC , When i print i only get CCC, it cuts the previous off.

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• Casting to a struct from LPVOID - C

  - by Jamie Keeling

  Hello, I am writing a simple console application which will allow me to create a number of threads from a set of parameters passed through the arguments I provide. DWORD WINAPI ThreadFunc(LPVOID threadData) { } I am packing them into a struct and passing them as a parameter into the CreateThread method and trying to unpack them by casting them to the same type as my struct from the LPVOID. I'm not sure how to cast it to the struct after getting it through so I can use it in the method itself, i've tried various combinations (Example attatched) but it won't compile. Struct: #define numThreads 1 struct Data { int threads; int delay; int messages; }; Call to method: HANDLE hThread; DWORD threadId; struct Data *tData; tData->threads = numThreads; tData->messages = 3; tData->delay = 1000; // Create child thread hThread = CreateThread( NULL, // lpThreadAttributes (default) 0, // dwStackSize (default) ThreadFunc, // lpStartAddress &tData, // lpParameter 0, // dwCreationFlags &threadId // lpThreadId (returned by function) ); My attempt: DWORD WINAPI ThreadFunc(LPVOID threadData) { struct Data tData = (struct Data)threadData; int msg; for(msg = 0; msg<5; msg++) { printf("Message %d from child\n", msg); } return 0; } Compiler error: error C2440: 'type cast' : cannot convert from 'LPVOID' to 'Data' As you can see I have implemented a way to loop through a number of messages already, I'm trying to make things slightly more advanced and add some further functionality.

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• pthread with unique struct as parameter C

  - by sergiobuj

  Hi, i have this piece of code that is giving me trouble. I know all the threads are reading the same struct. But i have no idea how to fix this. #include <pthread.h> #include <stdio.h> #include <stdlib.h> typedef struct { int a,b; } s_param; void * threadfunc(void *parm) { s_param *param2 = parm; printf("ID:%d and v:%d\n",param2->a,param2->b); pthread_exit(NULL); } int main(int argc, char **argv) { pthread_t thread[3]; int rc=0,i; void * status; for(i=0; i<3 ; ++i){ s_param param; param.b=10; param.a=i; rc = pthread_create(&thread[i], NULL, threadfunc, &param ); // !!!! if(rc){ exit(1); } } for(i=0; i<3 ; ++i){ pthread_join(thread[i],&status); } return 0; } output: ID:2 and v:10 ID:2 and v:10 ID:2 and v:10 and what i need: ID:0 and v:10 ID:1 and v:10 ID:2 and v:10 Thank you.

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• Calling functions from the Immediate Window during debugging -- advanced Visual Studio kung-fu test

  - by kizzx2

  I see some related questions have been asked, but they're either too advanced for me to grasp or lacking a step-by-step guide from start to finish (most of them end up being insider talk of their own experiment results). OK here it is, given this simple program: #include <stdio.h> #include <string.h> int main() { FILE * f; char buffer[100]; memset(buffer, 0, 100); fun(); f = fopen("main.cpp", "r"); fread(buffer, 1, 99, f); printf(buffer); fclose(f); return 0; } What it does is basically print itself (assume file name is main.cpp). Question How can I have it print another file, say foobar.txt without modifying the source code? It has something to do with running it through VS's, stepping through the functions and hijacking the FILE pointer right before fread() is called. No need to worry about leaking resources by calling fclose(). I tried the simple f = fopen("foobar.txt", "r") which gave CXX0017: Error: symbol "fopen" not found Any ideas?

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• Why doesn't gcc remove this check of a non-volatile variable?

  - by Thomas

  This question is mostly academic. I ask out of curiosity, not because this poses an actual problem for me. Consider the following incorrect C program. #include <signal.h> #include <stdio.h> static int running = 1; void handler(int u) { running = 0; } int main() { signal(SIGTERM, handler); while (running) ; printf("Bye!\n"); return 0; } This program is incorrect because the handler interrupts the program flow, so running can be modified at any time and should therefore be declared volatile. But let's say the programmer forgot that. gcc 4.3.3, with the -O3 flag, compiles the loop body (after one initial check of the running flag) down to the infinite loop .L7: jmp .L7 which was to be expected. Now we put something trivial inside the while loop, like: while (running) putchar('.'); And suddenly, gcc does not optimize the loop condition anymore! The loop body's assembly now looks like this (again at -O3): .L7: movq stdout(%rip), %rsi movl $46, %edi call _IO_putc movl running(%rip), %eax testl %eax, %eax jne .L7 We see that running is re-loaded from memory each time through the loop; it is not even cached in a register. Apparently gcc now thinks that the value of running could have changed. So why does gcc suddenly decide that it needs to re-check the value of running in this case?

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• GCC Dynamic library building problem

  - by Sirish Kumar

  I am new to linux, while compiling with dynamic library I am getting the segmentationfault error. I have two files ctest1.c void ctest1(int *i) { *i =10; } ctest2.c void ctest2(int *i) { *i =20; } I have compiled both files to a shared library named libtest.so using following command gcc -shared -W1,-soname,libtest.so.1 -o libtest.so.1.0.1 ctest1.o ctest2.o -lc And I have wrote another program prog.c which uses functions exported by this library prog.c #include void (ctest1)(int); void (ctest2)(int*); int main() { int a; ctest1(&a); printf("%d",a); return 0; } And when I have built the executable with following command gcc -Wall prog.c -L. -o prog But when I run the generated executable I get the SegmentationFault error. When I checked the header of prog with ldd it shows linux-vdso.so.1 = (0x00007f99dff000) libc.so.6 = /lib64/libc.so.6 (0x0007feeaa8c1000) /lib64/ld-linux-x86-64.so.2 (0x00007feeaac1c000) Can somebody tell what is the problem

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• How to properly use references with variadic templates

  - by Hippicoder

  I have something like the following code: template<typename T1, typename T2, typename T3> void inc(T1& t1, T2& t2, T3& t3) { ++t1; ++t2; ++t3; } template<typename T1, typename T2> void inc(T1& t1, T2& t2) { ++t1; ++t2; } template<typename T1> void inc(T1& t1) { ++t1; } I'd like to reimplement it using the proposed variadic templates from the upcoming standard. However all the examples I've seen so far online seem to be printf like examples, the difference here seems to be the use of references. I've come up with the following: template<typename T> void inc(T&& t) { ++t; } template<typename T,typename ... Args> void inc(T&& t, Args&& ... args) { ++t inc(args...); } What I'd like to know is: Should I be using r-values instead of references? Possible hints or clues as to how to accomplish what I want correctly. What guarantees does the new proposed standard provide wrt the issue of the recursive function calls, is there some indication that the above variadic version will be as optimal as the original? (should I add inline or some-such?)

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• Thread-local storage segfaults on NetBSD only?

  - by bortzmeyer

  Trying to run a C++ program, I get segmentation faults which appear to be specific to NetBSD. Bert Hubert wrote the simple test program (at the end of this message) and, indeed, it crashes only on NetBSD. % uname -a NetBSD golgoth 5.0.1 NetBSD 5.0.1 (GENERIC) #0: Thu Oct 1 15:46:16 CEST 2009 +stephane@golgoth:/usr/obj/sys/arch/i386/compile/GENERIC i386 % g++ --version g++ (GCC) 4.1.3 20080704 prerelease (NetBSD nb2 20081120) Copyright (C) 2006 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. % gdb thread-local-storage-powerdns GNU gdb 6.5 Copyright (C) 2006 Free Software Foundation, Inc. GDB is free software, covered by the GNU General Public License, and you are welcome to change it and/or distribute copies of it under certain conditions. Type "show copying" to see the conditions. There is absolutely no warranty for GDB. Type "show warranty" for details. This GDB was configured as "i386--netbsdelf"... (gdb) run Starting program: /home/stephane/Programmation/C++/essais/thread-local-storage-powerdns Program received signal SIGSEGV, Segmentation fault. 0x0804881b in main () at thread-local-storage-powerdns.cc:20 20 t_a = new Bogo('a'); (gdb) On other Unix, it works fine. Is there a known issue in NetBSD with C++ thread-local storage? #include <stdio.h> class Bogo { public: explicit Bogo(char a) { d_a = a; } char d_a; }; __thread Bogo* t_a; int main() { t_a = new Bogo('a'); Bogo* b = t_a; printf("%c\n", b->d_a); }

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• Is there a version of the removeElement function in Go for the vector package like Java has in its V

  - by Brian T Hannan

  I am porting over some Java code into Google's Go language and I converting all code except I am stuck on just one part after an amazingly smooth port. My Go code looks like this and the section I am talking about is commented out: func main() { var puzzleHistory * vector.Vector; puzzleHistory = vector.New(0); var puzzle PegPuzzle; puzzle.InitPegPuzzle(3,2); puzzleHistory.Push(puzzle); var copyPuzzle PegPuzzle; var currentPuzzle PegPuzzle; currentPuzzle = puzzleHistory.At(0).(PegPuzzle); isDone := false; for !isDone { currentPuzzle = puzzleHistory.At(0).(PegPuzzle); currentPuzzle.findAllValidMoves(); for i := 0; i < currentPuzzle.validMoves.Len(); i++ { copyPuzzle.NewPegPuzzle(currentPuzzle.holes, currentPuzzle.movesAlreadyDone); copyPuzzle.doMove(currentPuzzle.validMoves.At(i).(Move)); // There is no function in Go's Vector that will remove an element like Java's Vector //puzzleHistory.removeElement(currentPuzzle); copyPuzzle.findAllValidMoves(); if copyPuzzle.validMoves.Len() != 0 { puzzleHistory.Push(copyPuzzle); } if copyPuzzle.isSolutionPuzzle() { fmt.Printf("Puzzle Solved"); copyPuzzle.show(); isDone = true; } } } } If there is no version available, which I believe there isn't ... does anyone know how I would go about implementing such a thing on my own?

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• Retrieving and displaying AddressBook in Table view.

  - by Prash.......

  hi, I am developing an application in which i have to retrieve all Addressbook (Name & Phone No) records and Display it in table view, this is my Snippet for retrieving records from addressbook. NSArray *tableGroups; ABAddressBookRef m_addressbook = ABAddressBookCreate(); if (!m_addressbook) { NSLog(@"opening address book"); } CFArrayRef allPeople= ABAddressBookCopyArrayOfAllPeople(m_addressbook); CFIndex nPeople = ABAddressBookGetPersonCount(m_addressbook); NSMutableArray *selectableRows = [NSMutableArray array]; for (int i=0;i < nPeople;i++) { ABRecordRef ref = CFArrayGetValueAtIndex(allPeople,i); ABMutableMultiValueRef phoneMulti = ABRecordCopyValue(ref, kABPersonPhoneProperty); CFStringRef phoneNumber= ABMultiValueCopyValueAtIndex(phoneMulti, i); NSString *contactFirstLast = [NSString stringWithFormat:@"%@,%@", ABRecordCopyValue(ref, kABPersonFirstNameProperty),phoneNumber]; printf("%s\n", [contactFirstLast UTF8String]); [selectableRows addObject:[NSString stringWithFormat:contactFirstLast, i]]; CFRelease(phoneNumber); CFRelease(ref); CFRelease(contactFirstLast); CFRelease(phoneMulti); } tableGroups = [[NSArray alloc] initWithObjects:selectableRows, nil]; I am getting exception as "CFRetain" and apps get crash. Please suggest me proper solution for that..

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• Communication between parent and child

  - by Pierre

  Hi every one ! I have a little problem. I have to code a simple C application that creat a process and his child (fork()) and I have to do an operation. Parent initialize the values and child calculate. I write this : #include #include #include #include #include typedef struct { int op1; char op; int op2; }Operation; Operation *varOP; void finalResult() { float result = 0; if(varOP-op == '+') result = (varOP-op1 + varOP-op2); if(varOP-op == '-') result = (varOP-op1 - varOP-op2); if(varOP-op == '*') result = (varOP-op1 * varOP-op2); if(varOP-op == '+') result = (varOP-op1 / varOP-op2); printf("%f",result); } int main () { int p; varOP = (Operation *)malloc(sizeof(Operation)); p = fork(); if(p == 0) // If child { signal(SIGUSR1, finalResult ); pause(); } if(p 0) // If parent { varOP-op = '+'; varOP-op1 = 2; varOP-op2 = 3; kill(p, SIGUSR1); wait(NULL); } return 0; } But my child is never called. Is there something wrong with my code? Thanks for your help !

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• Segmentation fault with queue in C

  - by Trevor

  I am getting a segmentation fault with the following code after adding structs to my queue. The segmentation fault occurs when the MAX_QUEUE is set high but when I set it low (100 or 200), the error doesn't occur. It has been a while since I last programmed in C, so any help is appreciated. #include <stdio.h> #include <stdlib.h> #include <string.h> #define MAX_QUEUE 1000 struct myInfo { char data[20]; }; struct myInfo* queue; void push(struct myInfo); int queue_head = 0; int queue_size = 0; int main(int argc, char *argv[]) { queue = (struct myInfo*) malloc(sizeof(struct myInfo) * MAX_QUEUE); struct myInfo info; char buf[10]; strcpy(buf, "hello"); while (1) { strcpy(info.data, buf); push(info); } } void push(struct myInfo info) { int next_index = sizeof(struct myInfo) * ((queue_size + queue_head) % MAX_QUEUE); printf("Pushing %s to %d\n", info.data, next_index); *(queue + (next_index)) = info; queue_size++; } Output: Pushing hello to 0 Pushing hello to 20 ... Pushing hello to 7540 Pushing hello to 7560 Pushing hello to 7580 Segmentation fault

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• Serial: write() throttling?

  - by damian

  Hi everyone, I'm working on a project sending serial data to control animation of LED lights, which need to stay in sync with a sound engine. There seems to be a large serial write buffer (OSX (POSIX) + FTDI chipset usb serial device), so without manually restricting the transmission rate, the animation system can get several seconds ahead of the serial transmission. Currently I'm manually restricting the serial write speed to the baudrate (8N1 = 10 bytes serial frame per 8 bytes data, 19200 bps serial - 1920 bytes per second max), but I am having a problem with the sound drifting out of sync over time - it starts fine, but after 10 minutes there's a noticeable (100ms+) lag between the sound and the lights. This is the code that's restricting the serial write speed (called once per animation frame, 'elapsed' is the duration of the current frame, 'baudrate' is the bps (19200)): void BufferedSerial::update( float elapsed ) { baud_timer += elapsed; if ( bytes_written > 1024 ) { // maintain baudrate float time_should_have_taken = (float(bytes_written)*10)/float(baudrate); float time_actually_took = baud_timer; // sleep if we have > 20ms lag between serial transmit and our write calls if ( time_should_have_taken-time_actually_took > 0.02f ) { float sleep_time = time_should_have_taken - time_actually_took; int sleep_time_us = sleep_time*1000.0f*1000.0f; //printf("BufferedSerial::update sleeping %i ms\n", sleep_time_us/1000 ); delayUs( sleep_time_us ); // subtract 128 bytes bytes_written -= 128; // subtract the time it should have taken to write 128 bytes baud_timer -= (float(128)*10)/float(baudrate); } } } Clearly there's something wrong, somewhere. A much better approach would be to be able to determine the number of bytes currently in the transmit queue, and try and keep that below a fixed threshold. Any advice appreciated.

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• libpcap read packet size

  - by spicyramen

  I started to write an application which will read RTP/H.264 video packets from an existing .pcap file, I need to read the packet size. I tried to use packet-len or header-len, but it never displays the right number of bytes for packets (I'm using wireshark to verify packet size - under Length column). How to do it? This is part of my code: while (packet = pcap_next(handle,&header)) { u_char *pkt_ptr = (u_char *)packet; struct ip *ip_hdr = (struct ip *)pkt_ptr; //point to an IP header structure struct pcap_pkthdr *pkt_hdr =(struct pcap_pkthdr *)packet; unsigned int packet_length = pkt_hdr->len; unsigned int ip_length = ntohs(ip_hdr->ip_len); printf("Packet # %i IP Header length: %d bytes, Packet length: %d bytes\n",pkt_counter,ip_length,packet_length); Packet # 0 IP Header length: 180 bytes, Packet length: 104857664 bytes Packet # 1 IP Header length: 52 bytes, Packet length: 104857600 bytes Packet # 2 IP Header length: 100 bytes, Packet length: 104857600 bytes Packet # 3 IP Header length: 100 bytes, Packet length: 104857664 bytes Packet # 4 IP Header length: 52 bytes, Packet length: 104857600 bytes Packet # 5 IP Header length: 100 bytes, Packet length: 104857600 bytes Another option I tried is to use: pkt_ptr- I get: read_pcapfile.c:67:43: error: request for member ‘len’ in something not a structure or union

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• C# vs C - Big performance difference

  - by John

  I'm finding massive performance differences between similar code in C anc C#. The C code is: #include <stdio.h> #include <time.h> #include <math.h> main() { int i; double root; clock_t start = clock(); for (i = 0 ; i <= 100000000; i++){ root = sqrt(i); } printf("Time elapsed: %f\n", ((double)clock() - start) / CLOCKS_PER_SEC); } And the C# (console app) is: using System; using System.Collections.Generic; using System.Text; namespace ConsoleApplication2 { class Program { static void Main(string[] args) { DateTime startTime = DateTime.Now; double root; for (int i = 0; i <= 100000000; i++) { root = Math.Sqrt(i); } TimeSpan runTime = DateTime.Now - startTime; Console.WriteLine("Time elapsed: " + Convert.ToString(runTime.TotalMilliseconds/1000)); } } } With the above code, the C# completes in 0.328125 seconds (release version) and the C takes 11.14 seconds to run. The c is being compiled to a windows executable using mingw. I've always been under the assumption that C/C++ were faster or at least comparable to C#.net. What exactly is causing the C to run over 30 times slower? EDIT: It does appear that the C# optimizer was removing the root as it wasn't being used. I changed the root assignment to root += and printed out the total at the end. I've also compiled the C using cl.exe with the /O2 flag set for max speed. The results are now: 3.75 seconds for the C 2.61 seconds for the C# The C is still taking longer, but this is acceptable

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• Flex build error

  - by incrediman

  I'm totally new to flex. I'm getting a build error when using flex. That is, I've generated a .c file using flex, and, when running it, am getting this error: 1>lextest.obj : error LNK2001: unresolved external symbol "int __cdecl isatty(int)" (?isatty@@YAHH@Z) 1>C:\...\lextest.exe : fatal error LNK1120: 1 unresolved externals here is the lex file I'm using (grabbed from here): /*** Definition section ***/ %{ /* C code to be copied verbatim */ #include <stdio.h> %} /* This tells flex to read only one input file */ %option noyywrap %% /*** Rules section ***/ /* [0-9]+ matches a string of one or more digits */ [0-9]+ { /* yytext is a string containing the matched text. */ printf("Saw an integer: %s\n", yytext); } . { /* Ignore all other characters. */ } %% /*** C Code section ***/ int main(void) { /* Call the lexer, then quit. */ yylex(); return 0; } As well, why do I have to put a 'main' function in the lex syntax code? What I'd like is to be able to call yylex(); from another c file.

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• Get_user running at kernel mode returns error

  - by Fangkai Yang

  Hi, all, I have a problem with get_user() macro. What I did is as follows: I run the following program int main() { int a = 20; printf("address of a: %p", &a); sleep(200); return 0; } When the program runs, it outputs the address of a, say, 0xbff91914. Then I pass this address to a module running in Kernel Mode that retrieves the contents at this address (at the time when I did this, I also made sure the process didn't terminate, because I put it to sleep for 200 seconds... ): The address is firstly sent as a string, and I cast them into pointer type. int * ptr = (int*)simple_strtol(buffer, NULL,16); printk("address: %p",ptr); // I use this line to make sure the cast is correct. When running, it outputs bff91914, as expected. int val = 0; int res; res= get_user(val, (int*) ptr); However, res is always not 0, meaning that get_user returns error. I am wondering what is the problem.... Thank you!! -- Fangkai

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