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  • How do I indicate that a class doesn't support certain operators?

    - by romeovs
    I'm writing a class that represents an ordinal scale, but has no logical zero-point (eg time). This scale should permit addition and substraction (operator+, operator+=, ...) but not multiplication. Yet, I always felt it to be a good practice that when one overloads one operator of a certain group (in this case the math operators), one should also overload all the others that belong to that group. In this case that would mean I should need to overload the multiplication and division operators also, because if a user can use A+B he would probable expect to be able the other operators. Is there a method that I can use to throw an error for this at compiler time? The easiest method would be just no to overload the operators operator*, ... yet it would seem appropriate to add a bit more explaination than operator* is not know for class "time". Or is this something that I really should not care about (RTFM user)?

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  • Script throwing unexpected operator when using mysqldump

    - by Astron
    A portion of a script I use to backup MySQL databases has stopped working correctly after upgrading a Debian box to 6.0 Squeeze. I have tested the backup code via CLI and it works fine. I believe it is in the selection of the databases before the backup occurs, possibly something to do with the $skipdb variable. If there is a better way to perform the function then I'm will to try something new. Any insight would be greatly appreciated. $ sudo ./script.sh [: 138: information_schema: unexpected operator [: 138: -1: unexpected operator [: 138: mysql: unexpected operator [: 138: -1: unexpected operator Using bash -x script here is one of the iterations: + for db in '$DBS' + skipdb=-1 + '[' test '!=' '' ']' + for i in '$IGGY' + '[' mysql == test ']' + : + '[' -1 == -1 ']' ++ /bin/date +%F + FILE=/backups/hostname.2011-03-20.mysql.mysql.tar.gz + '[' no = yes ']' + /usr/bin/mysqldump --single-transaction -u root -h localhost '-ppassword' mysql + /bin/tar -czvf /backups/hostname.2011-03-20.mysql.mysql.tar.gz mysql.sql mysql.sql + rm -f mysql.sql Here is the code. if [ $MYSQL_UP = "yes" ]; then echo "MySQL DUMP" >> /tmp/update.log echo "--------------------------------" >> /tmp/update.log DBS="$($MYSQL -u $MyUSER -h $MyHOST -p"$MyPASS" -Bse 'show databases')" for db in $DBS do skipdb=-1 if [ "$IGGY" != "" ] ; then for i in $IGGY do [ "$db" == "$i" ] && skipdb=1 || : done fi if [ "$skipdb" == "-1" ] ; then FILE="$DEST$HOST.`$DATE +"%F"`.$db.mysql.tar.gz" if [ $ENCRYPT = "yes" ]; then $MYSQLDUMP -u $MyUSER -h $MyHOST -p"$MyPASS" $db > $db.sql && $TAR -czvf - $db.sql | $OPENSSL enc -aes-256-cbc -salt -out $FILE.enc -k $ENC_PASS && rm -f $db.sql else $MYSQLDUMP --single-transaction -u $MyUSER -h $MyHOST -p"$MyPASS" $db > $db.sql && $TAR -czvf $FILE $db.sql && rm -f $db.sql fi fi done fi

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  • Guru of the Week 2 no match for the operator==

    - by Adam
    From Guru of the Week 2. We have the function: string FindAddr(const list<Employee> l, string name) { for( list<Employee>::const_iterator i = l.begin(); i != l.end(); i++) { if( *i == name ) // here will be compilation error { return (*i).addr; } } return ""; } I added dummy Employee class to that: class Employee { string n; public: string addr; Employee(string name) : n(name) {} Employee() {} string name() const { return n; } operator string() { return n; } }; And got compilation error: error: no match for ‘operator==’ in ‘i.std::_List_iterator<_Tp>::operator* [with _Tp = Employee]() == name’ It works only if add operator== to Employee. But, Herb Sutter wrote that: The Employee class isn't shown, but for this to work it must either have a conversion to string or a conversion ctor taking a string. But Employee has a conversion function and conversion constructor as well. GCC version 4.4.3. Compiled normally, g++ file.cpp without any flags. There should be implicit conversion and it should work, why it doesn't?

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  • operator << : std::cout << i << (i << 1);

    - by Oops
    Hi, I use the stream operator << and the bit shifting operator << in one line. I am a bit confused, why does code A) not produce the same output than code B)? A) int i = 4; std::cout << i << " " << (i << 1) << std::endl; //4 8 B) myint m = 4; std::cout << m << " " << (m << 1) << std::endl; //8 8 class myint: class myint { int i; public: myint(int ii) { i = ii; } inline myint operator <<(int n){ i = i << n; return *this; } inline operator int(){ return i; } }; thanks in advance Oops

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  • Custom types as key for a map - C++

    - by Appu
    I am trying to assign a custom type as a key for std::map. Here is the type which I am using as key. struct Foo { Foo(std::string s) : foo_value(s){} bool operator<(const Foo& foo1) { return foo_value < foo1.foo_value; } bool operator>(const Foo& foo1) { return foo_value > foo1.foo_value; } std::string foo_value; }; When used with std::map, I am getting the following error. error C2678: binary '<' : no operator found which takes a left-hand operand of type 'const Foo' (or there is no acceptable conversion) c:\program files\microsoft visual studio 8\vc\include\functional 143 If I change the struct like the below, everything worked. struct Foo { Foo(std::string s) : foo_value(s) {} friend bool operator<(const Foo& foo,const Foo& foo1) { return foo.foo_value < foo1.foo_value; } friend bool operator>(const Foo& foo,const Foo& foo1) { return foo.foo_value > foo1.foo_value; } std::string foo_value; }; Nothing changed except making the operator overloads as friend. I am wondering why my first code is not working? Any thoughts?

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  • defining < operator for map of list iterators

    - by Adrian
    I'd like to use iterators from an STL list as keys in a map. For example: using namespace std; list<int> l; map<list<int>::const_iterator, int> t; int main(int argv, char * argc) { l.push_back(1); t[l.begin()] = 5; } However, list iterators do not have a comparison operator defined (in contrast to random access iterators), so compiling the above code results in an error: /usr/include/c++/4.2.1/bits/stl_function.h:227: error: no match for ‘operator<’ in ‘__x < __y’ If the list is changed to a vector, a map of vector const_iterators compiles fine. What is the appropriate way to define the operator < for list::const_iterator?

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  • Allow member to be const while still supporting operator= on the class

    - by LeopardSkinPillBoxHat
    I have several members in my class which are const and can therefore only be initialised via the initialiser list like so: class MyItemT { public: MyItemT(const MyPacketT& aMyPacket, const MyInfoT& aMyInfo) : mMyPacket(aMyPacket), mMyInfo(aMyInfo) { } private: const MyPacketT mMyPacket; const MyInfoT mMyInfo; }; My class can be used in some of our internally defined container classes (e.g. vectors), and these containers require that operator= is defined in the class. Of course, my operator= needs to do something like this: MyItemT& MyItemT::operator=(const MyItemT& other) { mMyPacket = other.mPacket; mMyInfo = other.mMyInfo; return *this; } which of course doesn't work because mMyPacket and mMyInfo are const members. Other than making these members non-const (which I don't want to do), any ideas about how I could fix this?

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  • Concatenation Operator

    - by Chaitanya
    This might be a silly question but it struck me, and here i ask. <?php $x="Hi"; $y=" There"; $z = $x.$y; $a = "$x$y"; echo "$z"."<br />"."$a"; ?> $z uses the traditional concatenation operator provided by php and concatenates, conversely $a doesn't, My questions: by not using the concatenation operator, does it effect the performance? If it doesn't why at all have the concatenation operator. Why have 2 modes of implementation when one does the work?

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  • Concatenation Operator - PHP

    - by Chaitanya
    This might be a silly question but it struck me, and here i ask. <?php $x="Hi"; $y=" There"; $z = $x.$y; $a = "$x$y"; echo "$z"."<br />"."$a"; ?> $z uses the traditional concatenation operator provided by php and concatenates, conversely $a doesn't, My questions: a. by not using the concatenation operator, does it effect the performance? b. If it doesn't why at all have the concatenation operator. c. Why have 2 modes of implementation when one does the work?

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  • Understanding pattern matching with cons operator

    - by Mathias
    In "Programming F#" I came across a pattern-matching like this one (I simplified a bit): let rec len list = match list with | [] -> 0 | [_] -> 1 | head :: tail -> 1 + len tail;; Practically, I understand that the last match recognizes the head and tail of the list. Conceptually, I don't get why it works. As far as I understand, :: is the cons operator, which appends a value in head position of a list, but it doesn't look to me like it is being used as an operator here. Should I understand this as a "special syntax" for lists, where :: is interpreted as an operator or a "match pattern" depending on context? Or can the same idea be extended for types other than lists, with other operators?

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  • Should I make OR operator to return const reference or just reference

    - by Yan Cheng CHEOK
    class error_code { public: error_code() : hi(0), lo(0) {} error_code(__int64 lo) : hi(0), lo(lo) {} error_code(__int64 hi, __int64 lo) : hi(hi), lo(lo) {} error_code& operator|=(const error_code &e) { this->hi |= e.hi; this->lo |= e.lo; return *this; } __int64 hi; __int64 lo; }; error_code operator|(const error_code& e0, const error_code& e1) { return error_code(e0.hi | e1.hi, e0.lo | e1.lo); } int main() { error_code e0(1); error_code e1(2); e0 |= e1; } I was wondering, whether I should make operator|= to return a const error_code& or error_code& ?

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  • Does dynamic_cast work inside overloaded operator delete ?

    - by iammilind
    I came across this: struct Base { void* operator new (size_t); void operator delete (void*); virtual ~Base () {} // <--- polymorphic }; struct Derived : Base {}; void Base::operator delete (void *p) { Base *pB = static_cast<Base*>(p); if(dynamic_cast<Derived*>(pB) != 0) { /* ... NOT reaching here ? ... */ } free(p); } Now if we do, Base *p = new Derived; delete p; Surprisingly, the condition inside the Base::delete is not satisfied Am I doing anything wrong ? Or casting from void* looses the information of Derived* ?

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  • (C++) What's the difference between these overloaded operator functions?

    - by cv3000
    What is the difference between these two ways of overloading the != operator below. Which is consider better? Class Test { ...// private: int iTest public: BOOL operator==(const &Test test) const; BOOL operator!=(const &Test test) const; } BOOL operator==(const &Test test) const { return (iTest == test.iTest); } //overload function 1 BOOL Test::operator!=(const &Test test) const { return !operator==(test); } //overload function 2 BOOL Test::operator!=(const &Test test) const { return (iTest != test.iTest); } I've just recently seen function 1's syntax for calling a sibling operator function and wonder if writing it that way provides any benefits.

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  • Why can't we have an immutable version of operator[] for map

    - by Yan Cheng CHEOK
    The following code works fine : std::map<int, int>& m = std::map<int, int>(); int i = m[0]; But not the following code : // error C2678: binary '[' : no operator... const std::map<int, int>& m = std::map<int, int>(); int i = m[0]; Most of the time, I prefer to make most of my stuff to become immutable, due to reason : http://www.javapractices.com/topic/TopicAction.do?Id=29 I look at map source code. It has mapped_type& operator[](const key_type& _Keyval) Is there any reason, why std::map unable to provide const mapped_type& operator[](const key_type& _Keyval) const

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  • Is the "==" operator required to be defined to use std::find

    - by user144182
    Let's say I have: class myClass std::list<myClass> myList where myClass does not define the == operator and only consists of public fields. In both VS2010 and VS2005 the following does not compile: myClass myClassVal = myList.front(); std::find( myList.begin(), myList.end(), myClassVal ) complaining about lack of == operator. I naively assumed it would do a value comparison of the myClass object's public members, but I am almost positive this is not correct. I assume if I define a == operator or perhaps use a functor instead, it will solve the problem. Alternatively, if my list was holding pointers instead of values, the comparison would work. Is this right or should I be doing something else?

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  • Entity Framework with SQL Server 2000 (APPLY Operator) issue

    - by How Lun
    Hello, I have a simple Linq query below: var seq = (from n in GetObjects() select n.SomeKey) .Distinct() .Count(); This query works find with SQL Server 2005 and above. But, this start to give headache when I hooked the EF to SQL Server 2000. Because EF is using APPLY operator which only SQL Server 2005 and above can be supported. I do not know why the hell EF is using APPLy operator instead of sub queries. My current work around is: var seq = (from n in GetObjects() select n.SomeKey) .Distinct() .ToList() .Count(); But, I can forsee more problems to come. The above query is just a simple one. Did anyone come across such issue? And how you guys work around it? Or is there a way to force EF not to use APPLY operator? Any help will be very much appreciated. How Lun.

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  • When is #include <new> library required in C++?

    - by Czarak
    Hi, According to this reference entry for operator new ( http://www.cplusplus.com/reference/std/new/operator%20new/ ) : Global dynamic storage operator functions are special in the standard library: All three versions of operator new are declared in the global namespace, not in the std namespace. The first and second versions are implicitly declared in every translation unit of a C++ program: The header does not need to be included for them to be present. This seems to me to imply that the third version of operator new (placement new) is not implicitly declared in every translation unit of a C++ program and the header <new> does need to be included for it to be present. Is that correct? If so, how is it that using both g++ and MS VC++ Express compilers it seems I can compile code using the third version of new without #include <new> in my source code? Also, the MSDN Standard C++ Library reference entry on operator new gives some example code for the three forms of operator new which contains the #include <new> statement, however the example seems to compile and run just the same for me without this include? // new_op_new.cpp // compile with: /EHsc #include<new> #include<iostream> using namespace std; class MyClass { public: MyClass( ) { cout << "Construction MyClass." << this << endl; }; ~MyClass( ) { imember = 0; cout << "Destructing MyClass." << this << endl; }; int imember; }; int main( ) { // The first form of new delete MyClass* fPtr = new MyClass; delete fPtr; // The second form of new delete char x[sizeof( MyClass )]; MyClass* fPtr2 = new( &x[0] ) MyClass; fPtr2 -> ~MyClass(); cout << "The address of x[0] is : " << ( void* )&x[0] << endl; // The third form of new delete MyClass* fPtr3 = new( nothrow ) MyClass; delete fPtr3; } Could anyone shed some light on this and when and why you might need to #include <new> - maybe some example code that will not compile without #include <new> ? Thanks.

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  • C++ addition overload ambiguity

    - by Nate
    I am coming up against a vexing conundrum in my code base. I can't quite tell why my code generates this error, but (for example) std::string does not. class String { public: String(const char*str); friend String operator+ ( const String& lval, const char *rval ); friend String operator+ ( const char *lval, const String& rval ); String operator+ ( const String& rval ); }; The implementation of these is easy enough to imagine on your own. My driver program contains the following: String result, lval("left side "), rval("of string"); char lv[] = "right side ", rv[] = "of string"; result = lv + rval; printf(result); result = (lval + rv); printf(result); Which generates the following error in gcc 4.1.2: driver.cpp:25: error: ISO C++ says that these are ambiguous, even though the worst conversion for the first is better than the worst conversion for the second: String.h:22: note: candidate 1: String operator+(const String&, const char*) String.h:24: note: candidate 2: String String::operator+(const String&) So far so good, right? Sadly, my String(const char *str) constructor is so handy to have as an implicit constructor, that using the explicit keyword to solve this would just cause a different pile of problems. Moreover... std::string doesn't have to resort to this, and I can't figure out why. For example, in basic_string.h, they are declared as follows: template<typename _CharT, typename _Traits, typename _Alloc> basic_string<_CharT, _Traits, _Alloc> operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs, const basic_string<_CharT, _Traits, _Alloc>& __rhs) template<typename _CharT, typename _Traits, typename _Alloc> basic_string<_CharT,_Traits,_Alloc> operator+(const _CharT* __lhs, const basic_string<_CharT,_Traits,_Alloc>& __rhs); and so on. The basic_string constructor is not declared explicit. How does this not cause the same error I'm getting, and how can I achieve the same behavior??

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  • What are All the Ways a Programmer Could use PHP to Send an Email?

    - by Alan Storm
    I'm looking for a list of built in PHP functions that a programmer could use to send an email. The obvious answer here is mail(), but I'm also looking for a list of functions someone might use to manually open a connection to an MTA, or spawn a process on the local machine which might in turn send an email using sendmail, postfix, etc. The context here is I want to scan a large, unknown codebase for code that's sending out email (because we already located a call to mail(), and that's not doing it)

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  • opendkim reporting read private key failed: no start line

    - by Bob
    I've set up keys with the following: opendkim-genkey -t -s mail -d test.com The private key (pertinent to this question) contains: -----BEGIN RSA PRIVATE KEY----- (some stuff here) -----END RSA PRIVATE KEY----- My opendkim.conf contains: Domain test.com KeyFile /etc/opendkim/dkim.private Selector mail I am then testing with: opendkim-testkey -d test.com -s mail -k /etc/mail/dkim.public Yet receive the following error: opendkim-testkey: PEM_read_bio_PrivateKey() failed error:0906D06C:PEM routines:PEM_read_bio:no start line The files exist and have opendkim as the user and group, and adequate permissions. Has anyone any advice?

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  • Webmin/ SpamAssassin doesn't appear to be 'learning' from forwarded examples of spam

    - by James
    I have spamtrap@ and hamtrap@ addresses set up on my mail server and forward examples of spam to the spamtrap address. I was hoping that after a few examples, SpamAssassin would 'learn' to identify the particular characteristics of spammy mail with common attributes, but this doesn't appear to be the case - it still gets delivered as normal mail. For example, some emails from the same sender and/ or with the same subject line, despite being sent several times to spamtrap@, are just delivered normally. Does it sound like SpamAssassin isn't working or correctly configured, or have I misunderstood a fundamental aspect of how it works?

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  • How common (or uncommon) is using full email address for email login?

    - by somecallmemike
    I was hoping you fine folks could comment on your experiences with using a full email address as a login name for an email service vs. using the username (everything before the @domain.tld). I ask because I have inherited a legacy email system in which usernames are completely unique, and users can log in via that username (to other services besides email as well) and I do not want to ask tens of thousands of users to have to update their email settings to support virtual domain hosting without good reason.

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  • whats the point of @localhost entries for a mail server

    - by radman
    Hi, After recently setting up a mail server I am now adding the users that I need. As part of the tutorial I followed I created root@localhost as an account and also a bunch of aliases (postmaster@localhost, webmaster@localhost etc). What is the point of having al these localhost addresses? it seems that no one can ever mail them directly... Also I am curious as to what targets I should include on my domain (like postmaster, root, webmaster etc) and what ramifications there might be for doing so?

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