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  • Isn't objective-c function parameter syntax weird? [closed]

    - by Haoest
    Consider the following method: +(void) myMethod:(int)arg1 **argument2**(int)arg2 **argument3**(int) arg3; See how the first argument, unlike the 2nd and 3rd, doesn't have a description, giving it an impression of bad symmetry. Also you would expect the extra typing will provide named argument as you pass it in, but you still have to pass them in the correct order. Can anyone help me make sense of this?

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  • How to find the differences between the values of a specific column based on a key?

    - by Holicreature
    I've two tables as purchase_details and invoice_details and i want to store the inventory/stock of each product from the data of these two tables. structure of purchase_details. 'pid', 'int(10)' 'product_id', 'int(10)' 'quantity', 'float(8,2)' 'amount', 'float(12,2)' 'expiry_date', 'date' structure of purchase_details. 'invoice_id', 'int(10) unsigned' 'product_id', 'int(10) unsigned' 'quantity', 'float(10,2)' 'price', 'float(12,2)' i want to calculate the total quantity of remaining stock (quantity of sum of products from purchase_details - quantity of sum of products from invoice_details). Product_id is would be same for the two tables. how can i proceed?

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  • C++ and preprocessor macro gotcha

    - by aaa
    hello. Appologies for yet another gotcha question. Can you figure out what is wrong with the statement below? gcc error states: "type name declared as function returning array". #define MACRO(a) (a)[1] class index { typedef int index_type[2]; index_type& operator[](int i); }; int k = 0; int i = MACRO(index()[k]); ps: is such questions are deemed too annoying, I am going to stop.

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  • Optimize SQL query (Facebook-like application)

    - by fabriciols
    My application is similar to Facebook, and I'm trying to optimize the query that get user records. The user records are that he as src ou dst. The src is in usermuralentry directly, the dst list are in usermuralentry_user. So, a entry can have one src and many dst. I have those tables: mysql> desc usermuralentry ; +-----------------+------------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +-----------------+------------------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | user_src_id | int(11) | NO | MUL | NULL | | | private | tinyint(1) | NO | | NULL | | | content | longtext | NO | | NULL | | | date | datetime | NO | | NULL | | | last_update | datetime | NO | | NULL | | +-----------------+------------------+------+-----+---------+----------------+ 10 rows in set (0.10 sec) mysql> desc usermuralentry_user ; +-------------------+---------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +-------------------+---------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | usermuralentry_id | int(11) | NO | MUL | NULL | | | userinfo_id | int(11) | NO | MUL | NULL | | +-------------------+---------+------+-----+---------+----------------+ 3 rows in set (0.00 sec) And the following query to retrieve information from two users. mysql> explain SELECT * FROM usermuralentry AS a , usermuralentry_user AS b WHERE a.user_src_id IN ( 1, 2 ) OR ( a.id = b.usermuralentry_id AND b.userinfo_id IN ( 1, 2 ) ); +----+-------------+-------+------+-------------------------------------------------------------------------------------------+------+---------+------+---------+------------------------------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+-------------------------------------------------------------------------------------------+------+---------+------+---------+------------------------------------------------+ | 1 | SIMPLE | b | ALL | usermuralentry_id,usermuralentry_user_bcd7114e,usermuralentry_user_6b192ca7 | NULL | NULL | NULL | 147188 | | | 1 | SIMPLE | a | ALL | PRIMARY | NULL | NULL | NULL | 1371289 | Range checked for each record (index map: 0x1) | +----+-------------+-------+------+-------------------------------------------------------------------------------------------+------+---------+------+---------+------------------------------------------------+ 2 rows in set (0.00 sec) but it is taking A LOT of time... Some tips to optimize? Can the table schema be better in my application?

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  • Converting a const char* into a double

    - by Koning Baard
    I am trying to convert a const char* to a double precision floating point number: int main(const int argc, const char *argv[]) { int i; double numbers[argc - 1]; for(i = 1; i < argc, i += 1) { /* -- Convert each argv into a double and put it in `number` */ } /* ... */ return 0; } Can anyone help me? Thanks

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  • C++ pimpl idiom wastes an instruction vs. C style?

    - by Rob
    (Yes, I know that one machine instruction usually doesn't matter. I'm asking this question because I want to understand the pimpl idiom, and use it in the best possible way; and because sometimes I do care about one machine instruction.) In the sample code below, there are two classes, Thing and OtherThing. Users would include "thing.hh". Thing uses the pimpl idiom to hide it's implementation. OtherThing uses a C style – non-member functions that return and take pointers. This style produces slightly better machine code. I'm wondering: is there a way to use C++ style – ie, make the functions into member functions – and yet still save the machine instruction. I like this style because it doesn't pollute the namespace outside the class. Note: I'm only looking at calling member functions (in this case, calc). I'm not looking at object allocation. Below are the files, commands, and the machine code, on my Mac. thing.hh: class ThingImpl; class Thing { ThingImpl *impl; public: Thing(); int calc(); }; class OtherThing; OtherThing *make_other(); int calc(OtherThing *); thing.cc: #include "thing.hh" struct ThingImpl { int x; }; Thing::Thing() { impl = new ThingImpl; impl->x = 5; } int Thing::calc() { return impl->x + 1; } struct OtherThing { int x; }; OtherThing *make_other() { OtherThing *t = new OtherThing; t->x = 5; } int calc(OtherThing *t) { return t->x + 1; } main.cc (just to test the code actually works...) #include "thing.hh" #include <cstdio> int main() { Thing *t = new Thing; printf("calc: %d\n", t->calc()); OtherThing *t2 = make_other(); printf("calc: %d\n", calc(t2)); } Makefile: all: main thing.o : thing.cc thing.hh g++ -fomit-frame-pointer -O2 -c thing.cc main.o : main.cc thing.hh g++ -fomit-frame-pointer -O2 -c main.cc main: main.o thing.o g++ -O2 -o $@ $^ clean: rm *.o rm main Run make and then look at the machine code. On the mac I use otool -tv thing.o | c++filt. On linux I think it's objdump -d thing.o. Here is the relevant output: Thing::calc(): 0000000000000000 movq (%rdi),%rax 0000000000000003 movl (%rax),%eax 0000000000000005 incl %eax 0000000000000007 ret calc(OtherThing*): 0000000000000010 movl (%rdi),%eax 0000000000000012 incl %eax 0000000000000014 ret Notice the extra instruction because of the pointer indirection. The first function looks up two fields (impl, then x), while the second only needs to get x. What can be done?

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  • Pair equal operator overloading for inserting into set

    - by Petwoip
    I am trying to add a pair<int,int> to a set. If a pair shares the same two values as another in the set, it should not be inserted. Here's my non-working code: typedef std::pair<int, int> PairInt; template<> bool std::operator==(const PairInt& l, const PairInt& r) { return (l.first == r.first && l.second == r.second) || (l.first == r.second && l.second == r.first); } int main() { std::set<PairInt> intSet; intSet.insert(PairInt(1,3)); intSet.insert(PairInt(1,4)); intSet.insert(PairInt(1,4)); intSet.insert(PairInt(4,1)); } At the moment, the (4,1) pair gets added even though there is already a (1,4) pair. The final contents of the set are: (1 3) (1 4) (4 1) and I want it to be (1 3) (1 4) I've tried putting breakpoints in the overloaded method, but they never get reached. What have I done wrong?

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  • Why does this C program compile?

    - by AdmiralJonB
    I've just come across someone's C code that I'm confused as to why it is compiling. There are two points I don't understand. First, the function prototype has no parameters compared to the actual function definition. Secondly, the parameter in the function definition doesn't have an type. #include <stdio.h> int func(); int func(param) { return param; } int main() { int bla = func(10); printf("%d",bla); } Could someone please explain to me why this works? I've tested it in a couple of compilers and it works fine.

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  • Sql join, 2 tables, same fields

    - by Lobuno
    I have 2 tables. To simplify: Table 1, users: userId int, userName nvarchar(50) Table 2 , messages: msgId int, msgFrom int, msgTo int... msg1 and msg2, both contain userId. Now I want to get all messages, but instead of the msgFrom I want the user name. I know what to do here: select tabMessages.*, tabUsers.userName as Sender from tabMessages inner join tabUsers on msgFrom=userId where msgId = @someParameter; Everything works fine and dandy. The same to get the user name instead of msgTo. Now the problem is, how do I do to get BOTH fields in the same call? I want to get the table as msgId, msgFrom, msgTo, Sender, Recipient. I have tried as: select tabMessages.*, tabUsers.userName as Sender, tabUsers.userName as Recipient from tabMessages inner join tabUsers on msgFrom=userId and msgTo=userId where msgId = @someParameter; but that doesn't work. I'm using Ms sql2000 by the way.

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  • Clustered index on frequently changing reference table of one or more foreign keys

    - by Ian
    My specific concern is related to the performance of a clustered index on a reference table that has many rapid inserts and deletes. Table 1 "Collection" collection_pk int (among other fields) Table 2 "Item" item_pk int (among other fields) Reference Table "Collection_Items" collection_pk int, item_pk int (combined primary key) Because the primary key is composed of both pks, a clustered index is created and the data physically ordered in the table according to the combined keys. I have many users creating and deleting collections and adding and removing items to those collections very frequently affecting the "Collection_Items" table, and its clustered index. QUESTION PART: Since the "Collection_Items" table is so dynamic, wouldn't there be a big performance hit on constantly resorting the table rows because of the clustered index ? If yes, what should I do to minimize this ?

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  • operator overloading and inheritance

    - by user168715
    I was given the following code: class FibHeapNode { //... // These all have trivial implementation virtual void operator =(FibHeapNode& RHS); virtual int operator ==(FibHeapNode& RHS); virtual int operator <(FibHeapNode& RHS); }; class Event : public FibHeapNode { // These have nontrivial implementation virtual void operator=(FibHeapNode& RHS); virtual int operator==(FibHeapNode& RHS); virtual int operator<(FibHeapNode& RHS); }; class FibHeap { //... int DecreaseKey(FibHeapNode *theNode, FibHeapNode& NewKey) { FibHeapNode *theParent; // Some code if (theParent != NULL && *theNode < *theParent) { //... } //... return 1; } }; Much of FibHeap's implementation is similar: FibHeapNode pointers are dereferenced and then compared. Why does this code work? (or is it buggy?) I would think that the virtuals here would have no effect: since *theNode and *theParent aren't pointer or reference types, no dynamic dispatch occurs and FibHeapNode::operator< gets called no matter what's written in Event.

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  • How to implement iterator as an attribute of a class in Java

    - by de3
    Hi, let's say I have this simple MyArray class, with two simple methods: add, delete and an iterator. In the main method we can see how it is supposed to be used: public class MyArray { int start; int end; int[] arr; myIterator it; public MyArray(){ this.start=0; this.end=0; this.arr=new int[500]; it=new myIterator(); } public void add(int el){ this.arr[this.end]=el; this.end++; } public void delete(){ this.arr[this.start]=0; this.start++; } public static void main(String[] args){ MyArray m=new MyArray(); m.add(3); m.add(299); m.add(19); m.add(27); while(m.it.hasNext()){ System.out.println(m.it.next()); } } And then MyIterator should be implemented somehow: import java.util.Iterator; public class myIterator implements Iterator{ @Override public boolean hasNext() { // TODO Auto-generated method stub return false; } @Override public Object next() { // TODO Auto-generated method stub return null; } @Override public void remove() { // TODO Auto-generated method stub } } MyIterator should iterate arr from MyArray class, from start to end values; both are also attributes of MyArray. So, as MyIterator should use MyArray attributes, how should MyIterator be implemented? Perhaps I can send the current object in the initialization: it=new myIterator(this); But I guess it's not the best soultion. Or maybe MyArray itself should implement Iterator interface? How is this solved?

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  • Performance implications of using a variable versus a magic number

    - by Nathan
    I'm often confused by this. I've always been taught to name numbers I use often using variables or constants, but if it reduces the efficiency of the program, should I still do it? Heres an example: private int CenterText(Font font, PrintPageEventArgs e, string text) { int recieptCenter = 125; int stringLength = Convert.ToInt32(e.Graphics.MeasureString(text, font)); return recieptCenter - stringLength / 2; } The above code is using named variables, but runs slower then this code: private int CenterText(Font font, PrintPageEventArgs e, string text) { return 125 - Convert.ToInt32(e.Graphics.MeasureString(text, font) / 2); } In this example, the difference in execution time is minimal, but what about in larger blocks of code?

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  • which is time consuming construct in following program?

    - by user388338
    while submitting a solution for practise problem 6(odd) i got TLE error but while using using print and scanf in place cin and cout my sol was submitted successfully with 0.77s time..i want to know how can i make it more efficient link to problem is codechef problem 6 #include<iostream> #include<cstdio> using namespace std; int main() {int n,N; scanf("%d",&n); for(int l=0;l<n;l++) { scanf("%d",&N); int i=0,x; if(N<=0) continue; for(;N>=(x=(2<<i));i++); printf("%d",x/2); cout<<"\n"; } }

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  • Mysql query question

    - by brux
    I have 2 tables: Customer: customerid - int, pri-key,auto fname - varchar sname -varchar housenum - varchar street -varchar Items: itemid - int,pri-key,auto type - varchar collectiondate - date releasedate - date customerid - int I need a query which will get me all items that have a releasedate 3 days prior to (and including) the current date. i.e The query should return customerid,fname,sname,street,housenum,type,releasedate for all items which have releasedate within (and including)3 days prior today thanks in advance

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  • MYSQL autoincrement a column or just have an integer, difference?

    - by David19801
    Hi, If I have a column, set as primary index, and set as INT. If I don't set it as auto increment and just insert random integers which are unique into it, does that slow down future queries compared to autincrementing? Does it speed things up if I run OPTIMIZE on a table with its primary and only index as INT? (assuming only 2 columns, and second column is just some INT value) (the main worry is the upper limit on the autoincrement as theres lots of adds and deletes in my table)

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  • Regular Expression to parse SQL Structure

    - by user351429
    I am trying to parse the MySQL data types returned by "DESCRIBE [TABLE]". It returns strings like: int(11) float varchar(200) int(11) unsigned float(6,2) I've tried to do the job using regular expressions but it's not working. PHP CODE: $string = "int(11) numeric"; $regex = '/(\w+)\s*(\w+)/'; var_dump( preg_split($regex, $string) );

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  • How to use templated classes as function arguments? (C++)

    - by Keand64
    I have a class declared along the lines of template<int a, int b> class C { public: array[a][b]; } and I want to use it as argument in a function like this: bool DoSomeTests(C &c1, C &c2); but when I compile, it tells me 'use of class template requires template argument list.' I tried template<int a, int b> bool DoSomeTests(C &c1, C &c2); but I get the same error. How can I fix this?

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  • Code Review: CLR RegexSubstring

    - by OMG Ponies
    Could this be better? .NET 2.0 compatibility for SQL Server 2005: public static SqlString RegexSubstring(SqlString regexpattern, SqlString sourcetext, SqlInt32 start_position) { SqlString result = null; if (!regexpattern.IsNull && !sourcetext.IsNull && !start_position.IsNull) { int start_location = (int)start_position >= 0 ? (int)start_position : 0; Regex RegexInstance = new Regex(regexpattern.ToString()); result = new SqlString(RegexInstance.Match(sourcetext.ToString(), (int)start_position).Value); } return result; }

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  • Simple loop, which one I would get more performance and which one is recommended? defining a variable inside a loop or outside of it?

    - by Grego
    Variable outside of the loop int number = 0; for(int i = 0; i < 10000; i++){ number = 3 * i; printf("%d",number); } or Variable inside of the loop for(int i = 0; i < 10000; i++){ int number = 3 * i; printf("%d",number); } Which one is recommended and which one is better in performance? Edit: This is just an example to exhibit what I mean, All I wanna know is if defining a variable inside a loop and outside a loop means the same thing , or there's a difference.

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  • Assign the results of a stored procedure into a variable in another stored procedure

    - by RHPT
    The title of this question is a bit misleading, but I couldn't summarize this very well. I have two stored procedures. The first stored procedure (s_proc1) calls a second stored procedure (s_proc2). I want to assign the value returned from s_proc2 to a variable in s_proc1. Currently, I'm calling s_proc2 (inside s_proc1) in this manner: EXEC s_proc2 @SiteID, @count = @PagingCount OUTPUT s_proc2 contains a dynamic query statement (for reasons I will not outline here). CREATE dbo.s_proc2 ( @siteID int, @count int OUTPUT ) AS DECLARE @sSQL nvarchar(100) DECLARE @xCount int SELECT @sSQL = 'SELECT COUNT(ID) FROM Authors' EXEC sp_ExecuteSQL @sSQL, N'@xCount int output', @xCount output SET @count = @xCount RETURN @count Will this result in @PagingCount having the value of @count? I ask because the result I am getting from s_proc1 is wonky. In fact, what I do get is two results. The first being @count, then the result of s_proc1 (which is incorrect). So, it makes me wonder if @PagingCount isn't being set properly. Thank you.

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  • ArrayIndexOutOfBoundsException trying to access data

    - by Eggy
    I am getting an array index out of bounds exception in the following code: for (int i=1; i<11; i++) { int a[][] = new int[10][3]; double LeftTrim = 1.0; double RightTrim = 1.0; a [i][0]=(int) (LeftTrim*((i)*25)); a [i][1]=(int) (RightTrim*((i)*25)); a [i][2]= 5000; //leftWheel, rightWheel, Milliseconds myf.setWheelVelocities(a[i][0], a[i][1], a[i][2]); JOptionPane.showMessageDialog(null, + (a [i][0] + a [i][1])/2 + "wheel velocities" + " | " + a [i][2] + " Milliseconds" + " Click OK to continue..."); } Every-time I reach the 9th increment Eclipse gives me the error "Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 10" I have to test the velocity up to 250, but when I reach 225 and I click 'Ok' on 'Click ok to continue..." this error shows up! Am I going out of the array bounds or something? Thank you!

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