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  • Is it good practice to initialize array in C/C++?

    - by sand
    I recently encountered a case where I need to compare two files (golden and expected) for verification of test results and even though the data written to both the files were same, the files does not match. On further investigation, I found that there is a structure which contains some integers and a char array of 64 bytes, and not all the bytes of char array were getting used in most of the cases and unused fields from the array contain random data and that was causing the mismatch. This brought me ask the question whether it is good practice to initialize the array in C/C++ as well, as it is done in Java?

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  • Magick++ in VS2010 - unresolved external symbol

    - by FlashFan
    Hey guys! I'm trying to use ImageMagick Magick++ for a C++ Project in VS2010. I installed the Library from here: klick Then in my Project, I added c:/program files/ImageMagick-6.6.6-Q16/include to the include folders. Then I tried to use Magick++ with this code: #include <Magick++.h> void main(int argc, char ** argv){ InitializeMagick(*argv); } But this does not work! VS2010 returns the following errors: error LNK2001: unresolved external symbol "__declspec(dllimport) void __cdecl Magick::InitializeMagick(char const *)" (__imp_?InitializeMagick@Magick@@YAXPBD@Z) error LNK1120: 1 unresolved externals What am I doing wrong? Thanks very much for your help!

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  • C++: Define simple string?

    - by Jason
    This thing is really wracking my mind. I'm learning C++ and I wanted to define a constant that I can use in another function, A short answer on how to do this will be fine.. Lets say at the beginning of my code I want to define this constant: //After #includes bool OS = 1; //1 = linux if (OS) { const ??? = "clear"; } else { const ??? = "cls"; } I don't know what type to use to define the "clear" string... I'm so confused. Later on I want to use it within a function: int foo() { system(::cls); //:: for global return 0; } How would I define the string up top, and use the string down below? I heard char only had one character and things... I'm not sure how to use , since it says it's converting string into const char or something.

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  • Cocoa multhithreads, locks don't work

    - by Igor
    I have a threadMethod which shows in console robotMotorsStatus every 0.5 sec. But when I try to change robotMotorsStatus in changeRobotStatus method I receive an exception. Where I need to put locks in that program. #import "AppController.h" @implementation AppController extern char *robotMotorsStatus; - (IBAction)runThread:(id)sender { [self performSelectorInBackground:@selector(threadMethod) withObject:nil]; } - (void)threadMethod { char string_to_send[]="QFF001100\r"; //String prepared to the port sending (first inintialization) string_to_send[7] = robotMotorsStatus[0]; string_to_send[8] = robotMotorsStatus[1]; while(1){ [theLock lock]; usleep(500000); NSLog (@"Robot status %s", robotMotorsStatus); [theLock unlock]; } } - (IBAction)changeRobotStatus:(id)sender { robotMotorsStatus[0]='1'; }

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  • I don't get this C/C++ Joke

    - by Buttercup
    After reading this article on thedailywtf.com, I'm not sure that I really got the joke. It says there that some guy changed the code from int function() { int x; char data_string[15]; ... x = 2; strcpy(data_string,"data data data"); ... } to int function() { int x = 2; char data_string[15] = "data data data"; ... } everywhere in the code and that for some reason did inflate the size of the executable from 1 to 2 CDs (or maybe it didn't do that?). Obviously I'm not familiar enough with C/C++ to get this joke, but what seems strangest is that the 2nd code listing seems "cleaner"—at least from what I've been told in school (that is that initializing variables is a good thing, not a bad one).

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  • Dynamic allocated array is not freed

    - by Stefano
    I'm using the code above to dynamically allocate an array, do some work inside the function, return an element of the array and free the memory outside of the function. But when I try to deallocate the array it doesn't free the memory and I have a memory leak. The debugger pointed to the myArray variable shows me the error CXX0030. Why? struct MYSTRUCT { char *myvariable1; int myvariable2; char *myvariable2; .... }; void MyClass::MyFunction1() { MYSTRUCT *myArray= NULL; MYSTRUCT *myElement = this->MyFunction2(myArray); ... delete [] myArray; } MYSTRUCT* MyClass::MyFunction2(MYSTRUCT *array) { array = (MYSTRUCT*)operator new(bytesLength); ... return array[X]; }

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  • Output unicode strings in Windows console app

    - by Andrew
    Hi I was trying to output unicode string to a console with iostreams and failed. I found this: Using unicode font in c++ console app and this snippet works. SetConsoleOutputCP(CP_UTF8); wchar_t s[] = L"èéøÞ???Sæca"; int bufferSize = WideCharToMultiByte(CP_UTF8, 0, s, -1, NULL, 0, NULL, NULL); char* m = new char[bufferSize]; WideCharToMultiByte(CP_UTF8, 0, s, -1, m, bufferSize, NULL, NULL); wprintf(L"%S", m); However, I did not find any way to output unicode correctly with iostreams. Any suggestions?

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  • c++ normalizing data sizes across systems

    - by Bocochoco
    I have a struct with three variables: two unsigned ints and an unsigned char. From my understanding, a c++ char is always 1 byte regardless of what operating system it is on. The same can't be said for other datatypes. I am looking for a way to normalize POD's so that when saved into a binary file, the resulting file is readable on any operating system that the code is compiled for. I changed my struct to use a 1-byte alignment by adding #pragma as follows: #pragma pack(push, 1) struct test { int a; } #pragma pack(pop) but that doesn't necessarily mean that int a is exactly 4 bytes on every os, I don't think? Is there a way to ensure that a file saved from my code will always be readable?

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  • Write to a binary file?

    - by rick irby
    Here is data structure w/ variables: struct Part_record { char id_no[3]; int qoh; string desc; double price: }; --- (Using "cin" to input data) --- Part_record null_part = {" ", 0," ",0.0}; --- --- file.seekg( -(long)sizeof(Part_record), ios::cur); file.write( ( char *)&part, sizeof(Part_record) ); The three variables, qoh, Id_no & price, write out correctly, but the "desc" variable is not right. Do I need to initialize Part_record some other way? It should be 20 characters in length. If you have enough info here, pls share your advice,thanks.

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  • [c]how to take input for a character pionter without using fget?

    - by ashish yadav
    consider the code include int main() {char* a; scanf("%s",a);//&a and &a[0] give same results-crashes printf("%s",); return 0; } why does this code results in crashing?whereas this code using character array works fine? include int main() {char a[100]; scanf("%s",&a[0]);//works fine printf("%s",a); return 0; } the difference being character array and pointer?but i knew that pointer just points to the first element that is &a[0] should work fine but upper code crashes for all three that is a,&a and &a[0]? the main thing i would to gather is how can i take input of a character pointer if i insist on using scanf only? i apologize if i am not clear. thanks in advance:)

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  • jQuery $.post & $.append & IE6

    - by Jim
    I'm having a weird problem with jQuery and IE6. Script works on IE7+ and with all other browsers I have tried it. I can't post the full script, but what it does is this: $.post("file.php",{'foo':'bar'},function(data){ $('#target').append(data) }) When I run the code in IE6, #target just shows ? and a white char with a hole in the middle. I have no idea what this second char is. My initial thought was that this was some sort of content-type problem because the file.php just echoes answer without any header information. I added Content-type: text/html with header() but didn't help. Any suggestions?

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  • Is there a simple script to convert C++ enum to string?

    - by Edu Felipe
    Suppose we have some named enums: enum MyEnum { FOO, BAR = 0x50 }; What I googled for is a script (any language) that scans all the headers in my project and generates a header with one function per enum. char* enum_to_string(MyEnum t); And a implementation with something like this: char* enum_to_string(MyEnum t){ switch(t){ case FOO: return "FOO"; case BAR: return "BAR"; default: return "INVALID ENUM"; } } The gotcha is really with typedefed enums, and unnamed C style enums. Does anybody know something for this? EDIT: The solution should not modify my source, except for the generated functions. The enums are in an API, so using the solutions proposed until now is just not an option.

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  • Dereferencing deleted pointers always result in an Access Violation ??

    - by m3rLinEz
    I have a very simple C++ code here: char *s = new char[100]; strcpy(s, "HELLO"); delete [] s; int n = strlen(s); If I run this code from Visual C++ 2008 by pressing F5 (Start Debugging,) this always result in crash (Access Violation.) However, starting this executable outside the IDE, or using the IDE's Ctrl+F5 (Start without Debugging) doesn't result in any crash. What could be the difference? I also want to know if it's possible to stably reproduce the Access Violation crash caused from accessing deleted area? Is this kind of crash rare in real-life?

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  • Why isn't my IO executed in order?

    - by HaskellElephant
    Hi, I'm having some fun learning about the haskell IO. However in my recent exploration of it I have encountered some problems with IO not executing in order, even inside a do construct. In the following code I am just keeping track of what cards are left, where the card is a tuple of chars (one for suit and one for value) then the user is continously asked for wich cards have been played. I want the putStr to be executed between each input, and not at the very end like it is now. module Main where main = doLoop cards doLoop xs = do putStr $ show xs s <- getChar n <- getChar doLoop $ remove (s,n) xs suits = "SCDH" vals = "A23456789JQK" cards = [(s,n) | s <- suits, n <- vals] type Card = (Char,Char) remove :: Card -> [Card] -> [Card] remove card xs = filter (/= card) xs

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  • C : Memory layout of C program execution

    - by pavun_cool
    Hi All , I wanted know how the kernel is providing memory for simple C program . For example : #include<stdio.h> #include<malloc.h> int my_global = 10 ; main() { char *str ; static int val ; str = ( char *) malloc ( 100 ) ; scanf ( "%s" , str ) ; printf( " val:%s\n",str ) ; } See, In this program I have used static , global and malloc for allocating dynamic memory So , how the memory lay out will be ... ? Any one give me url , which will have have details information about this process..

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  • Simple doubt related to strings in C (question in an interview)

    - by piemesons
    // The first example: char text[] = "henri"; char *p; p = text; *(p + 1) = 'E'; // Output = hEnri // Now If we want to remove the "e" ie hnri, we would go for????? *(p + 1)=????? Please dont say start copying the array. I am looking for the best solution. Its an interview question... EDIT I specially mentioned the question that i am not asking for the solution like start moving the element. I thought there must be some other good solution..

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  • How can I tell if an ADODB::_RecordsetPtr has already been created?

    - by scottm
    I am trying to write a class that uses ADO to retrieve SQL records. The intent is for the class to maintain one private recordset an other methods move forward, retrieve fields, etc. This is a basic example of my class: class SqlADO { private: ADODB::_RecordsetPtr m_recordset; public: void Open(); //open the connection void Execute(const char* sql); // creates or replaces current recordset void Next(); //moves recordset cursor forward void Field(const char* fieldName); //retrieves field name from current record of the recordset }; My Questions: In the Execute method, how can I check to see that the recordset instance has been created (or do I need to) so that I can close it first? Do you know of any good ADO COM Interop references?

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  • Constructing a function call in C

    - by 0x6adb015
    Given that I have a pointer to a function (provided by dlsym() for example) and a linked list of typed arguments, how can I construct a C function call with those arguments? Example: struct param { enum type { INT32, INT64, STRING, BOOL } type; union { int i32; long long i64; char *str; bool b; } value; struct param *next; }; int call_this(int (*function)(), struct param *args) { int result; /* magic here that calls function(), which has a prototype of f(int, long long, char *, bool); , when args consist of a linked list of INT32, INT64, STRING, BOOL types. */ return result; } The OS is Linux. I would like the solution to be portable across MIPS, PPC and x86 (all 32 bits) architecture, using GCC as the compiler. Thanks!

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  • Is there any memory leak in the normal routine of sqlite3_*()?

    - by reer
    A normal routine of sqlite3_prepare_v2() + sqlite3_step() + sqlite3_finalize() could contain leak. It sound ridiculous. But the test code seems to say it. Or I used the sqlite3_*() wrongly. Appreciate for any reply. __code________________________ include include // for usleep() include int multi_write (int j); sqlite3 *db = NULL; int main (void) { int ret = -1; ret = sqlite3_open("test.db", &db); ret = sqlite3_exec(db,"CREATE TABLE data_his (id INTEGER PRIMARY KEY, d1 CHAR(16))", NULL,NULL,NULL); usleep (100000); int j=0; while (1) { multi_write (j++); usleep (2000000); printf (" ----------- %d\n", j); } ret = sqlite3_close (db); return 0; } int multi_write (int j) { int ret = -1; char *sql_f = "INSERT OR REPLACE INTO data_his VALUES (%d, %Q)"; char *sql = NULL; sqlite3_stmt *p_stmt = NULL; ret = sqlite3_prepare_v2 (db, "BEGIN TRANSACTION", -1, &p_stmt, NULL); ret = sqlite3_step ( p_stmt ); ret = sqlite3_finalize ( p_stmt ); int i=0; for (i=0; i<100; i++) { sql = sqlite3_mprintf ( sql_f, j*100000 + i, "00000000000068FD"); ret = sqlite3_prepare_v2 (db, sql, -1, &p_stmt, NULL ); sqlite3_free ( sql ); //printf ("sqlite3_prepare_v2(): %d, %s\n", ret, sqlite3_errmsg (db)); ret = sqlite3_step ( p_stmt ); //printf ("sqlite3_step(): %d, %s\n", ret, sqlite3_errmsg (db)); ret = sqlite3_finalize ( p_stmt ); //printf ("sqlite3_finalize(): %d, %s\n\n", ret, sqlite3_errmsg (db)); } ret = sqlite3_prepare_v2 (db, "COMMIT TRANSACTION", -1, &p_stmt, NULL ); ret = sqlite3_step ( p_stmt ); ret = sqlite3_finalize ( p_stmt ); return 0; } __result________________________ And I watch the the process's run by top. At first, the memory statistics is: PID PPID USER STAT VSZ %MEM %CPU COMMAND 17731 15488 root S 1104 5% 7% ./sqlite3multiwrite When the printf() in while(1){} of main() prints the 150, the memory statistics is: PID PPID USER STAT VSZ %MEM %CPU COMMAND 17731 15488 root S 1552 5% 7% ./sqlite3multiwrite It sounds that after 150 for-cycles, the memory used by sqlite3multiwrite increase from 1104KB to 1552KB. What does it mean? memory leak or other thing?

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  • How do I get characters common to two vectors in C++?

    - by Sam Phelps
    I am trying to compare two vector objects, and return a single vector containing all the chars which appear in both vectors. How would I go about this without writing some horribly complex manual method which compares every char in the first vector to every char in the second vector and using an if to add it to a third vector (which would be returned) if they match. Maybe my lack of real experience with vectors is making me imagine this will be harder than it really is, but I suspect there is some simplier way which I have been unable to find through searching.

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  • Need help with displaying the message correctly in the pole display always starting at the beginning

    - by SA
    Hi, I am using an HP RS232 pole display with the following setting: Char type: USA/Europe (default) Command mode: EPSON (default) Baud rate: 9600, n , 8, 1 (default?) Passthru None (Default) Here's the code using System.IO.Ports; private SerialPort port; port = new SerialPort("COM2", 9600, Parity.None, 8, StopBits.One); port.Handshake = Handshake.None; Port.WriteLine("Welocome to something something"); It has 2 lines consisting of 20 characters each with a total of 40 characters. I have no control how and where the characters get displayed. I would like it to always begin on line 1 position 1 but as I said earlier how would I be able to do that. The same program if I run again and again it moves a character to the left. I have set it to accept ASCII char set and so I am able to type as is visble in the Writeline message

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  • Please see following code and answer

    - by user323422
    template <class T> class _cExplicitInstation { public: void show1(T c) { double d =10.02 ; std::cout<<c; } void show2(T d) { std::cout<<d; } }; template _cExplicitInstation<char>; template void _cExplicitInstation<int>::show1(int c); int main() { _cExplicitInstation<char> abc; _cExplicitInstation<int>().show2(10);// it should show error as i have // explicitly declare for show1() function but its working // can u tell why? }

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  • The ** idiom in C++ for object construction

    - by bobobobo
    In a lot of C++ API'S (COM-based ones spring to mind) that make something for you, the pointer to the object that is constructed is usually required as a ** pointer (and the function will construct and init it for you) You usually see signatures like: HRESULT createAnObject( int howbig, Object **objectYouWantMeToInitialize ) ; -- but you seldom see the new object being passed as a return value. Besides people wanting to see error codes, what is the reason for this? Is it better to use the ** pattern rather than a returned pointer for simpler operations such as: wchar_t* getUnicode( const char* src ) ; Or would this better be written as: void getUnicode( const char* src, wchar_t** dst ) ; The most important thing I can think of is to remember to free it, and the ** way, for some reason, tends to remind me that I have to deallocate it as well.

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  • Perfect Forwarding to async lambda

    - by Alexander Kondratskiy
    I have a function template, where I want to do perfect forwarding into a lambda that I run on another thread. Here is a minimal test case which you can directly compile: #include <thread> #include <future> #include <utility> #include <iostream> #include <vector> /** * Function template that does perfect forwarding to a lambda inside an * async call (or at least tries to). I want both instantiations of the * function to work (one for lvalue references T&, and rvalue reference T&&). * However, I cannot get the code to compile when calling it with an lvalue. * See main() below. */ template <typename T> std::string accessValueAsync(T&& obj) { std::future<std::string> fut = std::async(std::launch::async, [](T&& vec) mutable { return vec[0]; }, std::forward<T>(obj)); return fut.get(); } int main(int argc, char const *argv[]) { std::vector<std::string> lvalue{"Testing"}; // calling with what I assume is an lvalue reference does NOT compile std::cout << accessValueAsync(lvalue) << std::endl; // calling with rvalue reference compiles std::cout << accessValueAsync(std::move(lvalue)) << std::endl; // I want both to compile. return 0; } For the non-compiling case, here is the last line of the error message which is intelligible: main.cpp|13 col 29| note: no known conversion for argument 1 from ‘std::vector<std::basic_string<char> >’ to ‘std::vector<std::basic_string<char> >&’ I have a feeling it may have something to do with how T&& is deduced, but I can't pinpoint the exact point of failure and fix it. Any suggestions? Thank you! EDIT: I am using gcc 4.7.0 just in case this could be a compiler issue (probably not)

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  • Preprocessor directive to test if this is C or C++

    - by Collin
    I'm trying to find a standard macro which will test whether a header file is being compiled as C or as C++. The purpose of this is that the header may be included by either C or C++ code, and must behave slightly differently depending on which. Specifically: In C, I need this to be the code: extern size_t insert (const char*); In C++, I need this to be the code: extern "C" size_t insert (const char*); Additionally, is there a way to avoid putting #ifdef's around every declaration in the header?

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