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• Is this a correct syntax (c code found on wikipedia)?

  - by m4design

  I just found this code on wikipedia. Link: http://en.wikipedia.org/wiki/Sizeof#Use The code: /* the following code illustrates the use of sizeof * with variables and expressions (no parentheses needed), * and with type names (parentheses needed) */ char c; printf("%zu,%zu", sizeof c, sizeof(int)); It states that: "The z prefix should be used to print it, because the actual size can differ on each architecture." I tried it on my compiler, but it gives the following result: 'zu,zu'

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• How NOT to skip BOM info (FF FE) when using fread or ifstream?

  - by al_lea

  I'm trying to use fread/ifstream to read the first 2 bytes of a .csv with BOM info. But following code always skips the first two bytes (which are 'FF FE'): ifstream is; is.open (fn, ios::binary ); char buf[2]; is.read(buf, 2); is.close(); using FILE*/fread does no better.

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• C++ How fast is passing around objects?

  - by wndsr

  Assuming we are running a compiled C++ binary: Is passing around an int (e.g. function to function, or writing it into variables) slower than passing around structs/class objects like the following? class myClass { int a; int b; char c; vector d; string e; }

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• Is it possible to get a pointer to String^'s internal array in C++/CLI?

  - by CannibalSmith

  The goal is to avoid copying the string data when I need a const wchar_t*. The answer seems to be yes, but the function PtrToStringChars doesn't have its own MSDN entry (it's only mentioned in the KB and blogs as a trick). That made me suspicious and I want to check with you guys. Is it safe to use that function?

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• sed as grep + ignore # and match

  - by yael

  I have the following file example more somefile param=a b c d e f g z x w # param=a b c d e f g z x w I need to create with sed the following (should be one line if possible): Ignore # char in the beginning of line Match first the param string Second match the "a b c d e f g z x w" (like grep -w) and give exit status if success Something like .... sed "/^ *#/b; /\<param\>/" ....

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• How can I enter only numbers in TextBox using JavaScript without disable right click ?

  - by Space Cracker

  I want to allow numbers only to be allowed for a textbox and I already do it onkeydown event by allow only numbers and prevent ctrl+V but I have two problems : if I make right click then paste so any char can be entered and I want a solution without disable right click by oncontextmenu="return false;" if I drag and drop any text it will be entered Is there any solution that can work in all browsers without problem ?

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• Flexible array members in C - bad?

  - by Lionel

  I recently read that using flexible array members in C was poor software engineering practice. However, that statement was not backed by any argument. Is this an accepted fact? (Flexible array members are a C feature introduced in C99 whereby one can declare the last element to be an array of unspecified size. For example: ) struct header { size_t len; unsigned char data[]; };

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• How to test my application With STL such as vector to make sure weather it works or not in c++?

  - by Sam

  *we release and the acquire the pointer with the Linked_ptr in parameter */ Linked_ptr& operator=(const Linked_ptr& r) { if (this != &r) { release(); acquire(r); } return *this; }

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• How to copy a ram_base file to disk efficiently

  - by Hui Jin

  I want to copy a large a ram-based file (located at /dev/shm direcotry) to local disk, is there some way for an efficient copy instead of read char one by one or create another piece memory? I can use only C language here. Is there anyway that I can put the memory file directly to disk? Thanks!

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• Detect if class has overloaded function fails on Comeau compiler

  - by Frank

  Hi Everyone, I'm trying to use SFINAE to detect if a class has an overloaded member function that takes a certain type. The code I have seems to work correctly in Visual Studio and GCC, but does not compile using the Comeau online compiler. Here is the code I'm using: #include <stdio.h> //Comeau doesnt' have boost, so define our own enable_if_c template<bool value> struct enable_if_c { typedef void type; }; template<> struct enable_if_c< false > {}; //Class that has the overloaded member function class TestClass { public: void Func(float value) { printf( "%f\n", value ); } void Func(int value) { printf( "%i\n", value ); } }; //Struct to detect if TestClass has an overloaded member function for type T template<typename T> struct HasFunc { template<typename U, void (TestClass::*)( U )> struct SFINAE {}; template<typename U> static char Test(SFINAE<U, &TestClass::Func>*); template<typename U> static int Test(...); static const bool Has = sizeof(Test<T>(0)) == sizeof(char); }; //Use enable_if_c to only allow the function call if TestClass has a valid overload for T template<typename T> typename enable_if_c<HasFunc<T>::Has>::type CallFunc(TestClass &test, T value) { test.Func( value ); } int main() { float value1 = 0.0f; int value2 = 0; TestClass testClass; CallFunc( testClass, value1 ); //Should call TestClass::Func( float ) CallFunc( testClass, value2 ); //Should call TestClass::Func( int ) } The error message is: no instance of function template "CallFunc" matches the argument list. It seems that HasFunc::Has is false for int and float when it should be true. Is this a bug in the Comeau compiler? Am I doing something that's not standard? And if so, what do I need to do to fix it?

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• standard c library for escaping a string.

  - by rampion

  Is there a standard C library function to escape C-strings? For example, if I had the C string: char example[] = "first line\nsecond line: \"inner quotes\""; And I wanted to print "first line\nsecond line: \"inner quotes\"" Is there a library function that will do that transformation for me? Rolling my own just seems a little silly. Bonus points if I can give it a length to escape (so it stops before or beyond the \0).

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• m.find(...) == m.end() - which is used, iterator or const_iterator

  - by leeeroy

  std::map find/end both provides const_iterator and iterator, e.g. iterator end (); const_iterator end () const Out of curiosity,if I have a std::map , which will be called/compared here, an iterator or a const_iterator ? : if(m.find(key) != m.end()) { ... } And should I care ?

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• PHP: constant as variable in function

  - by m4recek

  I'm trying to use constant as a function paramter, is it possible to check type of this constant. Example of what I want: class ApiError { const INVALID_REQUEST = 200; } class Response { public function status(ApiError $status) { //function code here } } USE: $response = new Response(); $response->status(ApiError::INVALID_REQUEST); This shoud check that given $status is constant of class ApiError. Is something like this possible?

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• C++: Chr() and unichr() equivalent?

  - by alex

  I could have sworn I used a chr() function 40 minutes ago but can't find the file. I know it can go up to 256 so I use this: std::string chars = ""; chars += (char) 42; //etc So that's alright, but I really want to access unicode characters. Can I do (w_char) 512? Or maybe something just like the unichr() function in python, I just can't find a way to access any of those characters.

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• Do I need to cast the result of strtol to int?

  - by Kristo

  The following code does not give a warning with g++ 4.1.1 and -Wall. int octalStrToInt(const std::string& s) { return strtol(s.c_str(), 0, 8); } I was expecting a warning because strtol returns a long int but my function is only returning a plain int. Might other compilers emit a warning here? Should I cast the return value to int in this case as a good practice?

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• Why should we typedef a struct so often in C?

  - by Manoj Doubts

  I have seen many programs consisting of structures like the one below typedef struct { int i; char k; } elem; elem user; I have seen this many times. Why is it needed so often? Any specific reason or applicable area?

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• C++ STL: Trouble with iterators

  - by Rosarch

  I'm having a beginner problem: bool _isPalindrome(const string& str) { return _isPalindrome(str.begin(), str.end()); // won't compile } bool _isPalindrome(string::iterator begin, string::iterator end) { return begin == end || *begin == *end && _isPalindrome(++begin, --end); } What am I doing wrong here? Why doesn't str.begin() get type checked to be a string::iterator?

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• Access Voilation in std::pair

  - by sameer karjatkar

  I have an application which is trying to populate a pair . Out of no where the application crashes . The Windbg analysis on the crash dump suggest PRIMARY_PROBLEM_CLASS: INVALID_POINTER_READ DEFAULT_BUCKET_ID: INVALID_POINTER_READ STACK_TEXT: 0389f1dc EPFilter32!std::vector,std::allocator ::size+0xc INVALID_POINTER_READ_c0000005_Test.DLL!std::vector_std::pair_unsigned_int, unsigned_int_,std::allocator_std::pair_unsigned_int,unsigned_int___::size Following is the statement in the code where it fails const branch_info& b1 = en1.m_branches[i1]; where branch_info is std::pair and the en1.m_branches[i1] fetches me a pair value

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• Traversing stack and retrieving main arguments

  - by dlee313

  Given the size of the code of the main function in bytes passed as a parameter to a function, what is the best way to get to the base address for the main code and retrieve the first char * in the argv array?

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• Display unicode character in Actionscript

  - by Jan

  I have the unicode for that char, how do I display it? 0x023D2A textField.text = ???; i have have the name of the character. can I reference it by name?

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• How would I reverse an array of characters?

  - by jreicher

  Lets say I have an array of characters: char* foo = "abcdefg"; How would I reverse them but keep them within the array "foo"?

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• C/C++ efficient bit array

  - by aaa

  hi. Can you recommend efficient/clean way to manipulate arbitrary length bit array? right now I am using regular int/char bitmask, but those are not very clean when array length is greater than datatype length. std vector<bool> is not available for me. thanks

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• What happens when I throw an exception?

  - by helloWorld

  I have some technical questions. In this function: string report() const { if(list.begin() == list.end()){ throw "not good"; } //do something } If I throw the exception what is going on with the program? Will my function terminate or will it run further? If it terminates, what value will it return?

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• Have macro 'return' a value

  - by bobobobo

  I'm using a macro and I think it works fine - #define CStrNullLastNL(str) {char* nl=strrchr(str,'\n'); if(nl){*nl=0;}} So it works to zero out the last newline in a string, really its used to chop off the linebreak when it gets left on by fgets. So, I'm wondering if I can "return" a value from the macro, so it can be called like func( CStrNullLastNL( cstr ) ) ; Or will I have to write a function

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• What's wrong with my using argc/argv this way in c?

  - by user198729

  This works: int main( int argc, char *argv[]) { .... gtk_init(&argc, &argv); .... But this doesn't: int WINAPI WinMain (HINSTANCE p1, HINSTANCE p2, LPSTR argv, int argc) { .... gtk_init(&argc, &argv); .... Can someone point out what's wrong there?

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