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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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• regular expression on replace method of js not working

  - by user950146

  why this is not working var value = arr[row][col].replace(new RegExp('"', 'g'),'""'); Error : Webpage error details User Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; InfoPath.2; Tablet PC 2.0) Timestamp: Tue, 10 Apr 2012 11:22:01 UTC Message: Object doesn't support this property or method Line: 1041 Char: 25 Code: 0 URI: http://example.com/? Message: Object doesn't support this property or method Line: 1041 Char: 25 Code: 0 URI: http://example.com/? Message: Object doesn't support this property or method Line: 1041 Char: 25 Code: 0 URI: http://example.com/? Note: : Error copied directly from debugger of IE8

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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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• 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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• Swap byte 2 and 4 from integer

  - by czar x

  I had this interview question - Swap byte 2 and byte4 within an integer sequence. Integer is a 4byte wide i.e. 32 bits My approach was to use char *pointer and a temp char to swap the bytes. For clarity i have broken the steps otherwise an character array can be considered. unsigned char *b2, *b4, tmpc; int n = 0xABCD; b2 = &n; b2++; b4 = &n; b4 +=3; ///swap the values; tmpc = *b2; *b2 = *b4; *b4 = tmpc; Any other methods?

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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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• 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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• Dynamical array of strings in C

  - by Ir0nm

  I'm trying to make array of strings, I have function rLine which reads line from stdin, each inputted line I need to save in array, but I don't have any idea about number of inputted string lines. So I need to dynamically increase array size to store them, I wrote such code: char *res[2], *old = res; while( 1 ){ line = rLine( stdin ), len = strlen( line ); res[row] = (char*)malloc( len + 1); strcpy( res[row++], line); res = (char**) realloc( res, row ); /* adding 1 more row, not sure adding size row? */ if ( /*some cond*/ ) break; } But this code doesn't seem to work, how correctly declare array and increase it size?

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• Testing for the presence of a character in an string in C

  - by Prab

  What's wrong with this? #include <stdio.h> void main(){ char *s="some text"; printf("%d",is_in(s,'t')); } int is_in(char *s, char c){ while(*s){ if(*s==c) return 1; s++; } return 0; } I get the following compile time error with GCC: test.c:9: error: conflicting types for ‘is_in’ test.c:9: note: an argument type that has a default promotion can’t match an empty parameter name list declaration test.c:5: note: previous implicit declaration of ‘is_in’ was here

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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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• Defining a static array into a C or C++ source file.

  - by VansFannel

  Hello. I know this is a question that every programmer should know, but I do not know. Long time no C programming and I've forgotten a lot of things. My question is: I have three huge static arrays defined inside a header file. Someone told me that It's much better to declare them as extern in the header file, and define them in a single C or C++ source file. How can I do that? Here is my header file: #ifndef _TEMPLE_OBJECT_H_ #define _TEMPLE_OBJECT_H_ #define NUM_TEMPLE_OBJECT_VERTEX 10818 static const float TEMPLEVertices[NUM_TEMPLE_OBJECT_VERTEX * 3] = {...}; static const float TEMPLENormals[NUM_TEMPLE_OBJECT_VERTEX * 3] = {...}; static const float TEMPLETexCoords[NUM_TEMPLE_OBJECT_VERTEX * 3] = {...}; #endif If a use a C++ source file, may I need to define a class? Thank you.

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• Problems with first argument being string when overloading the + operator in C++

  - by Chris_45

  I have an selfmade Stringclass: //String.h String & operator = (const String &); String & operator = (char*); const String operator+ (String& s); const String operator+ (char* sA); . . //in main: String s1("hi"); String s2("hello"); str2 = str1 + "ok";//this is ok to do str2 = "ok" + str1;//but not this way //Shouldn't it automatically detect that one argument is a string and in both cases?

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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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• 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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• C++ Template Question

  - by user323422

  see following code and please clear doubts1. as ABC is template why it not showing error when we put defination of ABC class member function in test.cpp 2.if i put test.cpp code in test.h , then it working fine // test.h template <typename T> class ABC { public: void foo( T& ); void bar( T& ); }; // test.cpp template <typename T> void ABC<T>::foo( T& ) {} // definition template <typename T> void ABC<T>::bar( T& ) {} // definition template void ABC<char>::foo( char & ); // 1 // main.cpp #include "test.h" int main() { ABC<char> a; a.foo(); // working a.bar(); // link error }

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• How to define a custom iterator in C++

  - by Robert Martin

  I've seen a number of posts on SO about how to define custom iterators, but nothing that seems to exactly answers my question, which is... How do I create an iterator that hides a nested for loop? For instance, I have a class Foo, inside of the Foo is a Bar, and inside of the Bar is a string. I could write for (const Foo& foo : foo_set) for (const Bar& bar : foo.bar_set) if (bar.my_string != "baz") cout << bar.my_string << endl; but instead I want to be able to do something like: for (const string& good : foo_set) cout << good << endl; How do I do something like this?

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• Method sscanf() ambiguous behavior

  - by Carmen Cojocaru

  I am trying to understand how sscanf() works. I ran some examples from this page: http://docs.roxen.com/pike/7.0/tutorial/strings/sscanf.xml and they don't work on my platform. I can't understand why. For instance: "sscanf("4711bar", "%d%s", a, b);" makes the program exit with an error... Here is one of the examples that work: "sscanf("foo", "f%s", a);". Does anybody know why? Do they work on your platforms? Thank you. This is my code: int main(void){ char *b = (char*)malloc(sizeof(char)*100); int a = 0; sscanf("4711bar", "%d%s", a, b); printf("%d", a); printf("%s", b); }

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• trying to sort a simple string in c++

  - by every_answer_gets_a_point

  #include "stdio.h" #include "conio.h" #include <iostream> using namespace std; int main (void) { char my_char[] = "happy birthday"; int i; bool j=false; char my_char_temp[1]; do { for (i=0;i<sizeof(my_char)-2;i++) { j=false; if (my_char[i+1] < my_char[i]) { my_char_temp[0]=my_char[i+1]; my_char[i+1] = my_char[i]; my_char[i] = my_char_temp[0]; j=true; } } }while (j); cout << my_char; } what am i doing wrong? im just trying to sort the letters within the char the output i get is completely wrong

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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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• 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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• Determine an object's class returned by a factory method (Error: function does not take 1 arguments

  - by tzippy

  I have a factorymethod that either returns an object of baseclass or one that is of derivedclass (a derived class of baseclass). The derived class has a method virtual void foo(int x) that takes one argument. baseclass however has virtual void foo() without an argument. In my code, a factory method returns a pointer of type bar that definetly points to an object of class derivedclass. However since this is only known at runtime I get a compiler error saying that foo() does not take an argument. Can I cast this pointer to a pointer of type derivedclass? std::auto_ptr<baseclass> bar = classfactory::CreateBar(); //returns object of class derivedclass bar->foo(5); class baseclass { public: virtual void foo(); } class derivedclass : public baseclass { public: virtual void foo(int x); }

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• C++ rvalue temporaries in template

  - by aaa

  hello. Can you please explain me the difference between mechanism of the following: int function(); template<class T> void function2(T&); void main() { function2(function()); // compiler error, instantiated as int & const int& v = function(); function2(v); // okay, instantiated as const int& } is my reasoning correct with respect to instantiation? why is not first instantiated as const T&? Thank you

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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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• 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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• 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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