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• Proper way to handle issue when porting 32 to 64 bit. Conversion from DT1 to DT2 of greater size

  - by grobartn

  So I am trying to port 32 bit to 64 bit. I have turned on the VS2008 flag for detecting problems with 64 bit. I am trying following: char * pList = (char *)uiTmp); warning C4312: 'type cast' : conversion from 'unsigned int' to 'char *' of greater size Disregard the code itself. This is also true for any pointer, because 64 bit pointer is greater than 32 bit unsigned int or int for that purpose. Given that you have to cast smaller type to greater how would you go about doing it so it correctly on both 32/64 bit systems

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• Checking for an "end of line" in a C-string

  - by Numerator

  I would really love your help with the following problem: I want to get as an input from the user a maximum length of 30 chars string and check whether it contains an end of line. This is what I tried to write so far: int main(void) { int i; char* command = (char*)calloc(31, sizeof(char)); while (0 < 1) { scanf("%s", command); for (i = 0; i <= strlen(command); ++i) { if (command[i] == '\n') printf("here"); } if (strcmp(command, "quit") == 0) break; } The idea is to check whether the command given by the user as input is "legal" - that is of length < 31. when i run this code, it never prints "here" regardless of the length of input.

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• C++ string array from ifstream

  - by David Beck

  I have a program that I need to read in an array of strings from a file. The array must be C type strings (char * or char[]). Using the following code, I get a bad access error: for (i = 0; i < MAX_WORDS && !inputFile.eof(); i++) { inputFile >> words[i]; } words is declared as: char *words[MAX_WORDS];

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• C++ cin problems. not capturing input from user

  - by user69514

  I have the following method which is not capturing anything from the user.If I input New Band for the artist name, it only captures "New" and it lefts out "Band". If I use cin.getline() instead nothing is captured. Any ideas how to fix this? char* artist = new char [256]; char * getArtist() { cout << "Enter Artist of CD: " << endl; cin >> artist; cin.ignore(1000, '\n'); cout << "artist is " << artist << endl; return artist; }

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• C++ performance, optimizing compiler, empty function in .cpp

  - by Dodo

  I've a very basic class, name it Basic, used in nearly all other files in a bigger project. In some cases, there needs to be debug output, but in release mode, this should not be enabled and be a NOOP. Currently there is a define in the header, which switches a makro on or off, depending on the setting. So this is definetely a NOOP, when switched off. I'm wondering, if I have the following code, if a compiler (MSVS / gcc) is able to optimize out the function call, so that it is again a NOOP. (By doing that, the switch could be in the .cpp and switching will be much faster, compile/link time wise). --Header-- void printDebug(const Basic* p); class Basic { Basic() { simpleSetupCode; // this should be a NOOP in release, // but constructor could be inlined printDebug(this); } }; --Source-- // PRINT_DEBUG defined somewhere else or here #if PRINT_DEBUG void printDebug(const Basic* p) { // Lengthy debug print } #else void printDebug(const Basic* p) {} #endif

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• c++: strange syntax in what() method of std::exception

  - by Patrick Oscity

  When i am inheriting from std::exception in order to define my own exception type, i need to override the what() method, which has the following signature: virtual const char* what() const throw(); This definitely looks strange to me, like if there were two method names in the signature. Is this some very specific syntax, like with pure virtual methods, e.g.: virtual int method() const = 0; or is this a feature, that could somehow be used in another context, too? And if so, for what could it be used?

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• returning null or throwing an exception?

  - by MoKi

  I have the following types: typedef QPair < QTime , QTime > CalculatedTimeSlotRange; typedef QList < CalculatedTimeSlotRange > CalculatedTimeSlotRangeList; typedef QHash < quint8 , CalculatedTimeSlotRangeList > TimeSlotsTable; I have a function like the following: const CalculatedTimeSlotRangeList* TimeSlots::getCalculatedTimeSlotRangeList(const quint8 id) const { QHashIterator<quint8,CalculatedTimeSlotRangeList> it(mTimeSlotsTable); while (it.hasNext()) { it.next(); if(it.key() == id) { return &it.value(); } } return NULL; } as you can see my function returns a null if it fails to find a key that matches id. Is this correct? or should I just throw an exception if the key does not exist? how should i throw an exception for this situation?

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• Has anyone properly interpreted HTTP request based on this demo of winpcap?

  - by httpinterpret

  The example is here, and I tried it by changing the filter to tcp and dst port 80 and the following: void packet_handler(u_char *param, const struct pcap_pkthdr *header, const u_char *pkt_data) { .... ip_len = (ih->ver_ihl & 0xf) * 4; tcp_len = (((u_char*)ih)[ip_len + 12] >> 4) * 4; tcpPayload = (u_char*)ih + ip_len + tcp_len; /* start of url - skip "GET " */ url = tcpPayload + 4; end_url = strchr((char*)url, ' '); url_length = end_url - url; final_url = (u_char*)malloc(url_length + 1); strncpy((char*)final_url, (char*)url, url_length); final_url[url_length] = '\0'; printf("%s\n", final_url); .... } But through debug, I see tcpPayload is full of messy code,not supposed "GET ..." stuff. What's wrong with my implement?

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• Function to get a string and return same after processing in C

  - by C0de_Hard

  I am working on a code which requires a function. This function gets a string as input and returns a string. What I have planned so far is to get a str[], remove all $'s and spaces, and store this in another string which is returned later: char *getstring(char str[]) { int i=0; char rtn[255]; while (i<strlen(str)) { if (str[i] != " " || str[i] != "$" ) rtn[i] = str[i]; else rtn[i] = ''; } return str; } I dont feel like this will work. Any ideas?? :-S

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• Constructor Definition

  - by mctl87

  Ok so i have a class Vector: #include <cstdlib> class Vec { private: size_t size; int * ptab; public: Vec(size_t n); ~Vec() {delete [] ptab;} size_t size() const {return size;} int & operator[](int n) {return ptab[n];} int operator[](int n) const {return ptab[n];} void operator=(Vec const& v); }; inline Vec::Vec(size_t n) : size(n), ptab(new int[n]) { } and the problem is that in one of my homework exercises i have to extend constructor def, so all elements will be initialized with zeros. I thought i know the basics but cant get through this dynamic array -.- ps. sry for gramma and other mistakes ;)

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• seg violation using pycapsule_new

  - by user1733051

  I am trying some simple c API, where I am using PyCapsule_New to encapsulate a pointer. I am running into segment violation, can some body help me. mystruct *func1(int streamno, char mode,unsigned int options) { char * s; s=malloc(100); return s; } PyObject *Wrapper_func1(PyObject *self, PyObject *args) { int streamno; char mode; unsigned int options; mystruct* result; if (!PyArg_ParseTuple(args,"icI",&streamno,&mode,&options)) return NULL; result = func1(streamno,mode,options); return PyCapsule_New( result,NULL,NULL); }

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• Fstream's tellg / seekg returning higher value than expected. Help is appreciated

  - by Cosmin

  Why does this fail, it's supposed to be simple and work ? fisier.seekg(0, ios::end); long lungime = fisier.tellg(); This returns a larger value than that of the file resulting in a wrong char *continut = new char[lungime]; Any idea what the problem could be ? I also tried counting to the end of the file one char at a time, that rendered the same result, a higher number than expected. But upon using getline() to read one line at a time, it works, there are no extra spaces... Thank you

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• C++: Question about freeing memory

  - by Martijn Courteaux

  On Learn C++, they wrote this to free memory: int *pnValue = new int; // dynamically allocate an integer *pnValue = 7; // assign 7 to this integer delete pnValue; pnValue = 0; My question is: "Is the last statement needed to free the memory correctly, completly?" I thought that the pointer *pnValue was still on the stack and new doesn't make any sense to the pointer. And if it is on the stack it will be cleaned up when the application leaves the scope (where the pointer is declared in), isn't it?

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• Change master table PK and update related table FK (changing PK from Autoincrement to UUID on Mysql)

  - by eleonzx

  I have two related tables: Groups and Clients. Clients belongs to Groups so I have a foreign key "group_id" that references the group a client belongs to. I'm changing the Group id from an autoincrement to a UUID. So what I need is to generate a UUID for each Group and update the Clients table at once to reflect the changes and keep the records related. Is there a way to do this with multiple-table update on MySQL? Adding tables definitions for clarification. CREATE TABLE `groups` ( `id` char(36) NOT NULL, `name` varchar(255) DEFAULT NULL, `created` datetime DEFAULT NULL, `modified` datetime DEFAULT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8$$ CREATE TABLE `clients` ( `id` char(36) NOT NULL, `name` varchar(255) NOT NULL, `group_id` char(36) DEFAULT NULL, `active` tinyint(1) DEFAULT '1' PRIMARY KEY (`id`), KEY `fkgp` (`group_id`), CONSTRAINT `fkgp` FOREIGN KEY (`group_id`) REFERENCES `groups` (`id`) ON DELETE NO ACTION ON UPDATE CASCADE ) ENGINE=InnoDB DEFAULT CHARSET=utf8$$

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• boost variant static_visitor problem picking correct function

  - by Steve

  I'm sure I'm having a problem with template resolution here, but I'm not sure why I'm having the problem. I have a static visitor I'm passing to boost variant where i've had to do template specialization for certain cases. The case for everything except for MyClass should throw in the static_visitor below. Unfortunately, when the visitor is applied to pull a MyClass out, it selects the most generic case rather than the exact match. I would type each case explicitly, but that will be rather long. So, why is the compiler resolving the most generic case over the exact match, and is there anyway to fix it template<> class CastVisitor<MyClass>:public boost::static_visitor<MyClass> { public: template<typename U> MyClass operator()(const U & i) const { throw std::exception("Unable to cast"); } MyClass operator()(const MyClass& i) { return i; } };

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• C++ offset of member variables?

  - by anon

  I have: class Foo { int a; int b; std::string s; char d; }; Now, I want to know the offset of a, b, s, d given a Foo* I.e. suppose I have: Foo *foo = new Foo(); (char*) foo->b == (char*) foo + ?? ; // what expression should I put in ?

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• Copy Constructor in C++

  - by user265260

  i have this code #include <iostream> using namespace std; class Test{ public: int a; Test(int i=0):a(i){} ~Test(){ cout << a << endl; } Test(const Test &){ cout << "copy" << endl; } void operator=(const Test &){ cout << "=" << endl; } Test operator+(Test& p){ Test res(a+p.a); return res; } }; int main (int argc, char const *argv[]){ Test t1(10), t2(20); Test t3=t1+t2; return 0; } Output: 30 20 10 Why isnt the copy constructor called here?

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• aligning extern constants (gcc)

  - by ~buratinas

  I want to make some static constants globally visible. I'm pretty familiar how to do that in C++. The problem is that these constants need to be aligned to some exotic boundary. Do I have to specify the alignment in extern declaration? I'm using GCC4.5 in *.cpp file static const constant_t constant __attribute__((aligned(64))) = {blah,blah,blah}; in *.h file //Which one is correct? extern const constant_t constant; extern const constant_t constant __attribute__((aligned(64)));

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• Is it a good idea to include a large text variable in compiled code?

  - by gladman

  I am writing a program that produces a formatted file for the user, but it's not only producing the formatted file, it does more. I want to distribute a single binary to the end user and when the user runs the program, it will generate the xml file for the user with appropriate data. In order to achieve this, I want to give the file contents to a char array variable that is compiled in code. When the user runs the program, I will write out the char file to generate an xml file for the user. char* buffers = "a xml format file contents, \ this represent many block text \ from a file,..."; I have two questions. Q1. Do you have any other ideas for how to compile my file contents into binary, i.e, distribute as one binary file. Q2. Is this even a good idea as I described above?

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• how to use replace_regex_copy() from boost::algorithm library?

  - by Vincenzo

  This is my code: #include <string> #include <boost/algorithm/string/regex.hpp> string f(const string& s) { using namespace boost::algorithm; return replace_regex_copy(s, "\\w", "?"); } This is what compiler says: no matching function for call to ‘replace_regex_copy(const std::basic_string<char, std::char_traits<char>, std::allocator<char> >&, std::string, std::string) The link to the library: http://www.boost.org/doc/libs/1_43_0/doc/html/boost/algorithm/replace_regex_copy.html Could anyone please help? Thanks! ps. Boost library is in place, since other functions from it work fine.

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• passing different structs to a function in c

  - by clear2k

  I have different structures that need to be filled out the same way. The only difference is that they are filled based on different data. I was wondering if it's possible to pass different structures to a certain function. What I have in mind is something like: struct stu1 { char *a; int b; }; struct stu2 { char *a; int b; }; static struct not_sure **some_func(struct not_sure *not_sure_here, original_content_list) { // do something and return passed struct for(i=0; i<size_of_original_content_list; i++){ //fill out passed structure } return the_struct; } int main(int argc, char *argv[]) { return_struct1 = some_func(stu1); return_struct2 = some_func(stu2); // do something separate with each return struct... } Any comments will be appreciate it.

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• Speedup C++ code

  - by Werner

  Hi, I am writing a C++ number crunching application, where the bottleneck is a function that has to calculate for double: template<class T> inline T sqr(const T& x){return x*x;} and another one that calculates Base dist2(const Point& p) const { return sqr(x-p.x) + sqr(y-p.y) + sqr(z-p.z); } These operations take 80% of the computation time. I wonder if you can suggest approaches to make it faster, even if there is some sort of accuracy loss Thanks

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• NSMutableArray of Objects misbehaves ...

  - by iFloh

  I hope someone understands what happens to my NSMutableArray. I read records a, b, c, d from a database, load the fields into an object an add the object to an array. To do this I read the records into an instance of that object (tmpEvent) and add the Object to the target array (NSMutableArray myArray). the code looks like: for (condition) { tmpEvent.field1 = [NSString stringWithUTF8String:(char*)sqlite3_column_text(stmt, 0)]; tmpEvent.field2 = [NSString stringWithUTF8String:(char*)sqlite3_column_text(stmt, 1)]; tmpEvent.field3 = [NSString stringWithUTF8String:(char*)sqlite3_column_text(stmt, 2)]; NSLog(@"myArray: adding %@", tmpEvent.field1); [myArray addObject:tmpEvent]; } The NSLog shows myArray: adding a myArray: adding b myArray: adding c myArray: adding d Subsequent I enumerate the array (this can be in the same or a different method): for (myObject *records in myArray) { NSLog(@"iEvents value %@", records.field1); } The NSLog now shows: myArray value d myArray value d myArray value d myArray value d a mystery .... ??? any thoughts?

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• Is void *p = 0L valid?

  - by Artefacto

  In this answer, sassman initializes a pointer with: zend_class_entry* ce = 0L; My question is – is this valid? I would say it isn't, to initialize the variable with a null pointer either an unadorned (and possibly casted to void *) 0 constant, or some macro that evaluates to that such as NULL should be used. However, I can't find definitive language in the standard that supports this interpretation. All it says is: An integer constant expression with the value 0, or such an expression cast to type void *, is called a null pointer constant.

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• Converting Java code block to Objective-C

  - by user1123688

  I am trying to convert my Android app to iOS. This will be my first iOS app. I can't seem to translate this code properly. If someone wouldn't mind showing me how its done, that would be greatly appreciated. //scrambBase20 is a Byte array String descramble(String input){ char[] ret; ret = input.toCharArray(); int offset = -scrambBase20.length; for(int i=0;i<input.length();i++){ if(i%scrambBase20.length==0) offset+=scrambBase20.length; ret[scrambBase20[i%scrambBase20.length]+offset]=(char) ((byte) (input.charAt(i))^0x45); } String realRet = ""; for (char x : ret){ realRet+=x; } realRet = realRet.trim(); return realRet; }

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