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• memcpy() safety on adjacent memory regions

  - by JaredC

  I recently asked a question on using volatile and was directed to read some very informative articles from Intel and others discussing memory barriers and their uses. After reading these articles I have become quite paranoid though. I have a 64-bit machine. Is it safe to memcpy into adjacent, non-overlapping regions of memory from multiple threads? For example, say I have a buffer: char buff[10]; Is it always safe for one thread to memcpy into the first 5 bytes while a second thread copies into the last 5 bytes? My gut reaction (and some simple tests) indicate that this is completely safe, but I have been unable to find documentation anywhere that can completely convince me.

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• Unresolved External Symbol

  - by TomO

  I am working on wrapping a large number of .h and .lib files from native C++ to Managed C++ for eventual use as a referenced .dll in C#. I have the .lib files linked in and everything has been going smoothly so far. Upon wrapping the latest .h file, I hit a snag when 2 functions came back with the link error: error LNK2019: unresolved external symbol __imp__htonl@4 referenced in function "public: void __thiscall Field::setCharacter(unsigned char,int)" (?setCharacter@Field@@QAEXEH@Z) myutils.lib I have referenced "myutils.lib" in the linker options, so that shouldn't be the issue. What's strange is that I have about 20 functions in this particular .h file and all of the rest are linking just fine except for 3 functions. Any ideas?

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• How to execute unknown functions from dynamic load libraries?

  - by activenightly

  It's easy to load functions from dynamic libraries when you know this function in design time. just do something like this: int (*fn)(int); l0 = dlopen("./libfoo.so", RTLD_LAZY); if (!l0) { fprintf(stderr, "l0 %s\n", dlerror()); return 1; } fn = (int (*)(int))dlsym(l0, "foo"); if ((error = dlerror()) != NULL) { fprintf(stderr, "fn:%s\n", error); return 1; } x=(*fn)(y); ... How to execute library function when it's unknown in design time? In runtime you have a function name and array of arguments pointers and array of arguments sizes: char* fn_name="foo"; int foo_argc; void* foo_argv[]; int foo_argv_size[]; In scripting language it's a piece a cake task, but how to implement this nicely in c++?

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• Does this have anything to do with endian-ness?

  - by eSKay

  This piece of code: #include<stdio.h> void hello() { printf("hello\n"); } void bye() { printf("bye\n"); } int main() { printf("%p\n", hello); printf("%p\n", bye); return 0; } output on my machine: 0x80483f4 0x8048408 [second address is bigger in value] on Codepad 0x8048541 0x8048511 [second address is smaller in value] Does this have anything to do with endian-ness of the machines? If not, Why the difference in the ordering of the addresses? Also, Why the difference in the difference? 0x8048541 - 0x8048511 = 0x30 0x8048408 - 0x80483f4 = 0x14 Btw, I just checked. This code (taken from here) says that both the machines are Little-Endian #include<stdio.h> int main() { int num = 1; if(*(char *)&num == 1) printf("Little-Endian\n"); else printf("Big-Endian\n"); return 0; }

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• C - Call a function

  - by Pedro

  Hello. I want to get a value from a function in other function i think i have to call a function in other function, then call it on main, but how? void funcA(PEOPLE people[], int *total){ FILE *fp; char line[100]; fp=fopen("example.txt","r"); if(fp==NULL){ exit(1); } else{ fgets(line, 100, fp);//get a number from the txt total=atoi(linha);//convert to int } } void funcB(PEOPLE people[], int *total){ int i; for(i=0;i<total;i++){ printf("%s\n",people[i].name); } funcA(people,&total); } void main(){ PERSON person[100]; int *total; funcB(people,&total); } What i'm doing wrong?

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• Is there any way to pass an anonymous array as an argument in C++?

  - by Jeremy Friesner

  Hi all, I'd like to be able to declare an array as a function argument in C++, as shown in the example code below (which doesn't compile). Is there any way to do this (other than declaring the array separately beforehand)? #include <stdio.h> static void PrintArray(int arrayLen, const int * array) { for (int i=0; i<arrayLen; i++) printf("%i -> %i\n", i, array[i]); } int main(int, char **) { PrintArray(5, {5,6,7,8,9} ); // doesn't compile return 0; }

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• Loading Unmanaged C++ in C#. Error Attempted to read or write protected memory

  - by Thatoneguy

  I have a C++ function that looks like this __declspec(dllexport) int ___stdcall RegisterPerson(char const * const szName) { std::string copyName( szName ); // Assign name to a google protocol buffer object // Psuedo code follows.. Protobuf::Person person; person->set_name(copyName); // Error Occurs here... std::cerr << person->DebugString() << std::endl; } The corresponding C# code looks like this... [DllImport(@"MyLibrary.dll", SetLastError = true)] public static unsafe extern int RegisterPerson([MarshalAs(UnmanagedType.LPTStr)]string szName) Not sure why this is not working. My C++ library is compiled as Multi Threaded DLL with MultiByte encoding. Any help would be appreciated. I saw this is a common problem online but no answers lead me to a solution for my problem.

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• quick sort problem

  - by farka

  I use qsort from C libary and I have datatype Element_type **pElement and Element_type is struct typedef element_type {int ,char ....} example, and i call quicksor function with qsort(*pElement,iCountElement,(size_t)sizeof(Element_type),compare); and callback function static int compare(const void *p1, const void *p2) { Element_type *a1 = (Element_type *)p1; Element_type *a2 = (Element_type *)p2; return ( (a2)->iServiceId < (a1)->iServiceId ); } but I always get segmentation fault. Why?

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• how to listen to Enter button when using JOptionPane.showOptionDialog

  - by MemoryLeak

  I use: char[] password = null; JPasswordField jpf = new JPasswordField(30); java.lang.Object [] messageInput = { prompt, jpf }; java.lang.Object [] options = { jpf , "OK", "Cancel"}; int result = JOptionPane.showOptionDialog(null, messageInput, title, JOptionPane.OK_CANCEL_OPTION, JOptionPane.QUESTION_MESSAGE, null, options, ""); JOptionPane.showMessageDialog(null, result); if (result == 1) { password = jpf.getPassword(); } else if(result == JOptionPane.CANCEL_OPTION) { } return password; to get password, but this can not listen to the Enter button. I know if I set the options parameter to null, can make the dialog listen to "enter" button, but if I do that, the dialog don't focus to the textbox when show up. Can someone help me on this ? Thanks in advance !

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• Iterating through std queue

  - by Ockonal

  Hi, I'm trying to use BOOST_FOREACH for iterating through the std::queue. But there isn't iterators in that class cause I have an error: std::queue<std::string> someList; BOOST_FOREACH(std::string temp, someList) { std::cout << temp; } >no matching function for call to begin(...) >no type named ‘iterator’ in ‘class std::queue<std::basic_string<char> >’ I need in structure like: the first comes, the first goes away.

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• Does a servlet knows the encoding of the sent form that specified using http-equiv?

  - by Daziplqa

  Does a servlet knows the encoding of the sent form that specified using http-equiv? When I specify an encoding of a POSTed form using http-equiv like that: <HTML> <head> <meta http-equiv='Content-Type' content='text/html; charset=gb2312'/> </head> <BODY > <form name="form" method="post" > <input type="text" name="v_rcvname" value="????"> </form> </BODY> </HTML> And then at the servlet I use the method, request.getCharacterEncoding() I got null ! So, Is there a way that I can tell the server that I am encoding the data in some char encoding??

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• Is there any reason for a blocking call to winsock send() function on Vista to return immediately ?

  - by ivymike

  Hi All, Is there any reason for a blocking call to winsock's send() function on Vista to return immediately ? It works with expected delay on XP and below. I'm wondering if this has got anything to do with auto-tuning feature of Vista. Code: char *pBuffer; // pointer to data int bytes; // total size int i = 0, j=0; while (i < bytes) { j = send(m_sock, pBuffer+i, bytes-i, 0); i+=j; } Thanks, Pavan

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• Contents changed(cleared?) when access the pointer returned by std::string::c_str()

  - by justamask

  string conf()     {         vector v;         //..         v = func(); //this function returns a vector         return v[1];     }     void test()     {         const char* p = conf().c_str();         // the string object will be alive as a auto var         // so the pointer should be valid till the end of this function,right?           // ... lots of steps, but none of them would access the pointer p         // when access p here, SOMETIMES the contents would change ... Why?         // the platform is solaris 64 bit         // compiler is sun workshop 12         // my code is compiled as  ELF 32-bit MSB relocatable SPARC32PLUS Version 1, V8+ Required         // but need to link with some shared lib which are ELF 32-bit MSB dynamic lib SPARC Version 1, dynamically linked, stripped     }

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• Keeping historic of modification in a database.

  - by mada

  Hi, Im a j2ee developper & we are using hibernatne mapping with a postgres databasae. We have to keep track of any changes occurs in the databse , in others words alls previous & current value of any field should be saved & field can be various types (bytea, int, char...) With a simple table it is easy but we a graph of objets things are more difficult So we have , speaking in a UML point of view, a graph of objects to store in the database with every changes & the user. Any idea or pattern how to do that ? Thanks in advance.

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• How to generate random strings that match a given regexp?

  - by Pies

  Duplicate: Random string that matches a regexp No, it isn't. I'm looking for an easy and universal method, one that I could actually implement. That's far more difficult than randomly generating passwords. I want to create an application that takes a regular expression, and shows 10 randomly generated strings that match that expression. It's supposed to help people better understand their regexps, and to decide i.e. if they're secure enough for validation purposes. Does anyone know of an easy way to do that? One obvious solution would be to write (or steal) a regexp parser, but that seems really over my head. I repeat, I'm looking for an easy and universal way to do that. Edit: Brute force approach is out of the question. Assuming the random strings would just be [a-z0-9]{10} and 1 million iterations per second, it would take 65 years to iterate trough the space of all 10-char strings.

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• C pointer initialization and dereferencing, what's wrong here?

  - by randombits

  This should be super simple, but I'm not sure why the compiler is complaining here. #include <stdio.h> #include <stdlib.h> int main(int argc, char *argv[]) { int *n = 5; printf ("n: %d", *n); exit(0); } Getting the following complaints: foo.c: In function ‘main’: foo.c:6: warning: initialization makes pointer from integer without a cast I just want to print the value that the pointer n references. I'm dereferencing it in the printf() statement and I get a segmentation fault. Compiling this with gcc -o foo foo.c.

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• How to call operator<< on "this" in a descendant of std::stringstream?

  - by romkyns

  class mystream : public std::stringstream { public: void write_something() { this << "something"; } }; This results in the following two compile errors on VC++10: error C2297: '<<' : illegal, right operand has type 'const char [10]' error C2296: '<<' : illegal, left operand has type 'mystream *const ' Judging from the second one, this is because what this points at can't be changed, but the << operator does (or at least is declared as if it does). Correct? Is there some other way I can still use the << and >> operators on this?

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• how to represent negative number to array of integers ?

  - by stdnoit

  I must convert string of 1324312321 to array of integers in java this is fine. I could use integer parseint and string substring method but how do I repesent -12312312 to my original array of integer.. the fact that - is a char / string and convert to array of integer would alter the value ( even though I convert - to integer-equivalent , it would change the rest of 12312312) it must be an array of integers and how should I convert negative numbers and still keeep the same value somehow reminding me of two complements trick but i dont think i need to go down to binary level in my program.. any other trick for doing this? thanks!

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• C++, Get text from a website, part 3

  - by pure841

  So, thanks for all the help guys, I am just have one last problem, I am putting the website source in a char var, and then reading the product title (I have gotten that), however it only works if I take part of the source, or only the html from one of the featured products on neweggs page. I think the program is crashing, because it doesnt know which title to pick when I need to get all three titles and put them into an array. Any ideas? Thanks. Here is the parser code: http://paste2.org/p/809045 Any solution is greatly appreciated.

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• Fastest algorithm to check if a number is pandigital?

  - by medopal

  Pandigital number is a number that contains the digits 1..number length. For example 123, 4312 and 967412385. I have solved many Project Euler problems, but the Pandigital problems always exceed the one minute rule. This is my pandigital function: private boolean isPandigital(int n){ Set<Character> set= new TreeSet<Character>(); String string = n+""; for (char c:string.toCharArray()){ if (c=='0') return false; set.add(c); } return set.size()==string.length(); } Create your own function and test it with this method int pans=0; for (int i=123456789;i<=123987654;i++){ if (isPandigital(i)){ pans++; } } Using this loop, you should get 720 pandigital numbers. My average time was 500 millisecond. I'm using Java, but the question is open to any language.

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• Is it possible to establish default values for inherited fields in subclasses?

  - by Christian Mann

  I'm trying to establish a default value for inherited fields from superclasses. So, my class hierarchy is thus: Character - Enemy - Boss                 \                   - Hero Each Character has a public static char avatar to represent him on an ASCII playing field. How do I set a default value for the avatar of each class inherited from Character? Thank you!

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• [C] Read line from file without knowing the line length.

  - by ryyst

  Hi, I want to read in a file line by line, without knowing the line length before. Here's what I got so far: int ch = getc(file); int length = 0; char buffer[4095]; while (ch != '\n' && ch != EOF) { ch = getc(file); buffer[length] = ch; length++; } printf("Line length: %d characters.", length); I can now figure out the line length, but only for lines that are shorter than 4095 characters. Is there a better way to do this (I already used fgets() but got told it wasn't the best way)? --Ry

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• How to get path to current exe file on Linux?

  - by user1519221

  The code below gives current path to exe file on Linux: #include <iostream> std::string getExePath() { char result[ PATH_MAX ]; ssize_t count = readlink( "/proc/self/exe", result, PATH_MAX ); return std::string( result, (count > 0) ? count : 0 ); } int main() { std::cout << getExePath() << std::endl; return 0; } The problem is that when I run it gives me current path to exe and name of the exe, e.g.: /home/.../Test/main.exe I would like to get only /home/.../Test/ I know that I can parse it, but is there any nicer way to do that?

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• add different characters to a NSString one by one??

  - by hemant

  i am retrieving different characters from a string by using thsi function and adding 5 to them to display the corresponding character for eg. 'a' displays 'f' and 'h' displays 'm'.. but the problem is that i am not able to add these characters into a string which i can use to display to display like 'fm'...can anyone help?? heres the code strResult(mutablestring) is getting null only. `str=@"John"; int a=[str length]; for(i=0;i char ch=[str characterAtIndex:i]; ch=ch+5; temp=[NSString stringWithFormat:@"%c",ch]; [strResult appendString:temp]; NSLog(@"%c",ch); }`

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• Association in Entity Framework 4

  - by Marsharks

  I have two tables, a problem table and a problem history table. As you can expect, a problem can have many histories associated with it. CREATE TABLE [dbo].[Problem]( [Last_Update] [datetime] NULL, [Problem_Id] [int] NOT NULL, [Incident_Count] [int] NULL ) ALTER TABLE [dbo].[Problem] ADD CONSTRAINT [PK_Problem] PRIMARY KEY CLUSTERED ( [Problem_Id] ASC ) CREATE TABLE [dbo].[Problem_History]( [Last_Update] [datetime] NULL, [Problem_Id] [int] NOT NULL, [Severity_Chg_Flag] [char](1) NULL ) ALTER TABLE [dbo].[Problem_History] ADD [Create_DateTime] [datetime] NOT NULL ALTER TABLE [dbo].[Problem_History] WITH CHECK ADD CONSTRAINT [FK_Problem_History_Problem] FOREIGN KEY([Problem_Id]) REFERENCES [dbo].[Problem] ([Problem_Id]) The problem is when I drag this into an Entity Model, the associations are not included. Any ideas? I would like to point out that the problem history table has no separate key of its own, it shares the problem id

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