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• What does =*> mean with regards to context free grammars?

  - by incrediman

  I've been reading a couple books/online references about compiler theory, and keep seeing that particular operator coming up every once in a while (as seen here), specifically when the current topic is context free grammars. What does it mean? As well, how does it differ from =>? Explanations with examples distinguishing => from =*> would be most helpful.

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• C++: ptr->hello(); /* VERSUS */ (*ptr).hello();

  - by Joey

  i was learning about c++ pointers... so the "-" operator seemed strange to me... instead of ptr-hello(); one could write (*ptr).hello(); because it also seems to work, so i thought the former is just a more convenient way is that the case or is there any difference?

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• How to process this string via regular expression

  - by iiduce

  my string style like this: expression1/field1+expression2*expression3+expression4/field2*expression5*expression6/field3 a real style mybe like this: computer/(100)+web*mail+explorer/(200)*bbs*solution/(300) "+" and "*" represent operator "computer","web"...represent expression (100),(200) represent field num . field num may not exist. I want process the string to this: /(100)+web*+explorer/(200)bbs/(300) rules like this: if expression length is more than 3 and its field is not (200), then add brackets to it.

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• c#: adding two strings

  - by every_answer_gets_a_point

  i am doing: html = new WebClient().DownloadString("http://www.google.com/search?sourceid=chrome&ie=UTF-8&q=" + biocompany); and i am getting the error: Error 1 Operator '&' cannot be applied to operands of type 'string' and 'string' but i am not even using the & ! please help!

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• Can I use "map" as a substitute for "for each"/"for in"?

  - by John Mee

  For a little while now javascript has the "map" function to loop over arrays. It appears possible to use it as a 'foreach' operator for example: var arr = ['a','b','c'] var doubles = arr.map(function(val){ return val + val }) Is this better or worse than saying for(var i in arr){ ... 50/50: saves having to use the index but adds a callback; it doesn't seem very common so I hesitate to use it but still want to.

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• [UNIX] Is it safe to pipe the output of several parallel processes to one file using >> ?

  - by conradlee

  I'm scraping data from the web, and I have several processes of my scraper running in parallel. I want the output of each of these processes to end up in the same file. As long as lines of text remain intact, I the order of the lines does not matter. In UNIX, can I just pipe the output of each process to the same file using the operator?

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• How can an object not be compared to null?

  - by ProfK

  I have an 'optional' parameter on a method that is a KeyValuePair. I wanted an overload that passes null to the core method for this parameter, but in the core method, when I want to check if the KeyValuePair is null, I get the following error: Operator '!=' cannot be applied to operands of type System.Collections.Generic.KeyValuePair<string,object>' and '<null>. How can I not be allowed to check if an object is null?

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• c#: xdocument and reading xsi:nil="true" gives "String was not recognized as a valid DateTime"

  - by DingoCC

  Happily reading xml with var q2 = from c in xmlDoc.Descendants("Ticket") select new { Responded_Date = (DateTime)c.Element("Responded_Date") } However when the tag is <Responded_Date xsi:nil="true" /> I get "String was not recognized as a valid DateTime". I don't wish to use the null coalescing operator but simply to take the null and insert into datatable

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• Error Message 'class::function' : illegal call of non-static member function

  - by shak

  i was trying to call a static function of class using scope resolution operator, the way to access static function but still generating error. what are the possibilities.

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• Getting value depedning on two boolean attrinutes.[Nested ifs]

  - by uswaretech

  I have two fields start_time end_time - can be null Now, depending on this I needs to differentiate between three states Scheduled in future, Currently running Completed in past Since mysql IF operator can not be nested, (Or I cant find an easy way to nest them), I cant find how to get the three state status.

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• How is it possible to legally write ::: in C++ and ??? in C#?

  - by daveny

  These questions are a kind of game, and I did not find the solution for them. It is possible to write ::: in C++ without using quotes or anything like this and the compiler will accept it (macros are prohibited too). And the same is true for C# too, but in C#, you have to write ???. I think C++ will use the :: scope operator and C# will use ? : , but I do not know the answers to them. Any idea?

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• [bash] checking wget's return value [if]

  - by wwrob

  I'm writing a script to download a bunch of files, and I want it to inform when a particular file doesn't exist. r=`wget -q www.someurl.com` if [ $r -ne 0 ] then echo "Not there" else echo "OK" fi But it gives the following error on execution: ./file: line 2: [: -ne: unary operator expected What's wrong?

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• Is there any standard delete functor?

  - by FredOverflow

  I am looking for a functor that deletes its argument: template<class T> struct delete_functor { void operator()(T* p) { delete p; } }; Is there something like this in std, tr1 or boost?

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• Problem with receiving data form serial port in c#?

  - by moon

  hello i have problem with receiving data from serial port in c# in am inserting a new line operator at the end of data buffer. then i send this data buffer on serial port, after this my c# GUI receiver will take this data via Readline() function but it always give me raw data not the actual one how to resolve this problem.

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• How do I create a duplicate instance of object contained in a shared pointer in c++?

  - by user367848

  I have an object which has both a copy constructor and assignment operator defined. It is enclosed inside a shared pointer. I want to make another shared pointer that contains a copy of the original shared pointer (i.e. new shared pointer to a new memory location, which however, has the same data as the original object). Thanks for any assistance.

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• What does [a|b|c] evaluate to in Prolog?

  - by Ambrose

  The pipe operator in prolog returns one or more atomic Heads and a Tail list. ?- [a,b,c] = [a,b|[c]]. true. Nesting multiple pipes in a single match can be done similar to this: ?- [a,b,c] = [a|[b|[c]]]. true. What does the statement [a|b|c] infer about a, b and c?

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• Float conditional in bash

  - by Werner

  Hi, in bash I need to compare two float numbers, one which I define in the script and the other read as paramter, for that I do: if [[ $aff -gt 0 ]] then a=b echo "xxx "$aff #echo $CX $CY $CZ $aff fi but I get the error: [[: -309.585300: syntax error: invalid arithmetic operator (error token is ".585300") What is wrong? Thanks

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• Why would you avoid C++ keywords in Java?

  - by Joshua Swink

  A popular editor uses highlighting to help programmers avoid using C++ keywords in Java. The following words are displayed using the same colors as a syntax error: auto delete extern friend inline redeclared register signed sizeof struct template typedef union unsigned operator Why would this be considered important?

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• LESS THAN OR EQUAL TO IN Oracle SQL

  - by Jasim

  updated_date = 08-Jun-2010; I have a query like this select * from asd whre updated_date <= todate('08-Jun-2010', 'dd-MM-yy'); but i am not getting any result. it is wotking only if todate is 09-Jun-2010... ie my equalto operator is not working properly. y is it like that ny help?

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• Javascript date comparison

  - by Art

  Why does equality operator return false in the first case? var a = new Date(2010, 10, 10); var b = new Date(2010, 10, 10); alert(a == b); // <- returns false alert(a.getTime() == b.getTime()); // returns true Why?

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• python: equivalent to Javascript "||" to override non-truthful value

  - by Jason S

  In Javascript I can do this: function A(x) { return x || 3; } This returns 3 if x is a "non-truthful" value like 0, null, false, and it returns x otherwise. This is useful for empty arguments, e.g. I can do A() and it will evaluate as 3. Does Python have an equivalent? I guess I could make one out of the ternary operator a if b else c but was wondering what people use for this.

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• Help with SQL query in C#

  - by DanSogaard

  I'm trying to rename the columns. The syntax should be the column name between double quotes incase of two words, like this: SELECT p_Name "Product Name" from items So I'm trying to do it in C# code like this: string sqlqry1 = "SELECT p_Name \"Prodcut Name\" from items"; But I get an error: Syntax error (missing operator) in query expression 'p_Name "Prodcut Name"'. It seems am having somthing wrong with the quotes, but I can't figure out.

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• Heap Behavior in C++

  - by wowus

  Is there anything wrong with the optimization of overloading the global operator new to round up all allocations to the next power of two? Theoretically, this would lower fragmentation at the cost of higher worst-case memory consumption, but does the OS already have redundant behavior with this technique, or does it do its best to conserve memory? Basically, given that memory usage isn't as much of an issue as performance, should I do this?

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• boost::function function pointer to parameters?

  - by high6

  How does boost::function take a function pointer and get parameters from it? I want wrap a function pointer so that it can be validated before being called. And it would be nice to be able to call it like boost::function is with the () operator and not having to access the function pointer member. Wrapper func; func(5); //Yes :D func.Ptr(5) //Easy to do, but not as nice looking

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• VBA: Validate List settings

  - by stanigator

  Sub Macro1() ' ' Macro1 Macro ' ' Worksheets("Drop-down").Select For i = 1 To 10 ActiveSheet.Cells(i, 2).Select With Selection.Validation .Delete ' Error in this line .Add Type:=xlValidateList, AlertStyle:=xlValidAlertStop, Operator:= _ xlBetween, Formula1:=Range(Worksheets("Misc").Cells(2, i), Worksheets("Misc").Cells(2, i).End) .IgnoreBlank = True .InCellDropdown = True .InputTitle = "" .ErrorTitle = "" .InputMessage = "" .ErrorMessage = "" .ShowInput = True .ShowError = True End With Next i End Sub I'm getting an error in the line below the comment, yet I don't know how to fix it. It would be great to hear some suggestions. Thanks in advance!

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