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  • SCons and dependencies for python function generating source

    - by elmo
    I have an input file data, a python function parse and a template. What I am trying to do is use parse function to get dictionary out of data and use that to replace fields in template. Now to make this a bit more generic (I perform the same action in few places) I have defined a custom function to do so. Below is definition of custom builder and values is a dictionary with { 'name': (data_file, parse_function) } (you don't really need to read through this, I simply put it here for completeness). def TOOL_ADD_FILL_TEMPLATE(env): def FillTemplate(env, output, template, values): out = output[0] subs = {} for name, (node, process) in values.iteritems(): def Process(env, target, source): with open( env.GetBuildPath(target[0]), 'w') as out: out.write( process( source[0] ) ) builder = env.Builder( action = Process ) subs[name] = builder( env, env.GetBuildPath(output[0])+'_'+name+'_processed.cpp', node )[0] def Fill(env, target, source): values = dict( (name, n.get_contents()) for name, n in subs.iteritems() ) contents = template[0].get_contents().format( **values ) open( env.GetBuildPath(target[0]), 'w').write( contents ) builder = env.Builder( action = Fill ) builder( env, output[0], template + subs.values() ) return output env.Append(BUILDERS = {'FillTemplate': FillTemplate}) It works fine when it comes to checking if data or template changed. If it did it rebuilds the output. It even works if I edit process function directly. However if my process function looks like this: def process( node ): return subprocess(node) and I edit subprocess the change goes unnoticed. Is there any way to get correct builds without making process functions being always invoked?

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  • ruby on rails basics help

    - by CHID
    Hi, i created a scaffolded application in rails by the name of product. The product_controller.rb file contains the following. class ProductsController ApplicationController def new @product = Product.new respond_to do |format| format.html # new.html.erb format.xml { render :xml = @product } end end def create @product = Product.new(params[:product]) respond_to do |format| if @product.save flash[:notice] = 'Product was successfully created.' format.html { redirect_to(@product) } format.xml { render :xml = @product, :status = :created, :location = @product } else format.html { render :action = "new" } format.xml { render :xml = @product.errors, :status = :unprocessable_entity } end end end Now when the url http://localhost:3000/products/create is given Where new product link is clicked, control is transferred to new definition in the controller class and then an instance variable @product is created. BUT WHERE IS THIS VARIABLE PASSED? The funtion inturn calls new.rhtml which contains <% form_for(@product) do |f| % #all form elments declaration <% f.submit "Create" % <%= end % Here @product is initialized in the controller file and passed to this new.rhtml. So where does form_for(@product) gets the data? How does the control gets tranfered to create function in controller file when submit button is clicked? No where action is specified to the controller file. in the create function, wat does redirec_to(@product) specify where @product is an object received from the new.html file... I am very much confused on the basics of ROR. Somone pls help me clarify this. pardon me for making such a big post. I have lots of doubts in this single piece of code

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  • Get Username from a Cookie

    - by craphunter
    Hi, I use the backend solution from django. I just want to get a username from the cookie or the session_key to get to know the user. How I can do it? from django.contrib.auth.models import User from django.contrib.sessions.models import Session def start(request, template_name="registration/my_account.html"): user_id = request.session.get('session_key') if user_id: name = request.user.username return render_to_response(template_name, locals()) else: return render_to_response('account/noauth.html') Only else is coming up. What am I doing wrong? Am I right then that authenticated means he is logged in? -- Okay this I got! Firstly, if you have some clarification to a question, update the question, don't post an answer or (even worse) another question, as you have done. Secondly, if the user is logged out, by definition he doesn't have a username. I mean the advantage of Cookies is to identify a user again. I just want to place his name on the webpage. Even if he is logged out. Or isnt't it possible?

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  • How can I skip some block content while reading in Perl.

    - by Nano HE
    Hello. I plan to skip the block content which include the start line of "MaterializeU4()" with the subroutin() read_block below. But failed. # Read a constant definition block from a file handle. # void return when there is no data left in the file. # Otherwise return an array ref containing lines to in the block. sub read_block { my $fh = shift; my @lines; my $block_started = 0; while( my $line = <$fh> ) { # how to correct my code below? I don't need the 2nd block content. $block_started++ if ( ($line =~ /^(status)/) && (index($line, "MaterializeU4") != 0) ) ; if( $block_started ) { last if $line =~ /^\s*$/; push @lines, $line; } } return \@lines if @lines; return; } Data as below: __DATA__ status DynTest = <dynamic 100> vid = 10002 name = "DynTest" units = "" status VIDNAME9000 = <U4 MaterializeU4()> vid = 9000 name = "VIDNAME9000" units = "degC" status DynTest = <U1 100> vid = 100 name = "Hello" units = "" Output: <StatusVariables> <SVID logicalName="DynTest" type="L" value="100" vid="10002" name="DynTest" units=""></SVID> <SVID logicalName="VIDNAME9000" type="L" value="MaterializeU4()" vid="9000" name="VIDNAME9000" units="degC"></SVID> <SVID logicalName="DynTest" type="L" value="100" vid="100" name="Hello" units=""></SVID> </StatusVariables> [Updated] I print the value of index($line, "MaterializeU4"), it output 25. Then I updated the code as below $block_started++ if ( ($line =~ /^(status)/) && (index($line, "MaterializeU4") != 25) Now it works. Any comments are welcome about my practice. Thank you.

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  • Global name not defined error in Django/Python trying to set foreignkey

    - by Mark
    Summary: I define a method createPage within a file called PageTree.py that takes a Source model object and a string. The method tries to generate a Page model object. It tries to set the Page model object's foreignkey to refer to the Source model object which was passed in. This throws a NameError exception! I'm trying to represent a website which is structured like a tree. I define the Django models Page and Source, Page representing a node on the tree and Source representing the contents of the page. (You can probably skip over these, this is a basic tree implementation using doubly linked nodes). class Page(models.Model): name = models.CharField(max_length=50) parent = models.ForeignKey("self", related_name="children", null=True); firstChild = models.ForeignKey("self", related_name="origin", null=True); nextSibling = models.ForeignKey("self", related_name="prevSibling", null=True); previousSibling = models.ForeignKey("self", related_name="nxtSibling", null=True); source = models.ForeignKey("Source"); class Source(models.Model): #A source that is non dynamic will be refered to as a static source #Dynamic sources contain locations that are names of functions #Static sources contain locations that are places on disk name = models.CharField(primary_key=True, max_length=50) isDynamic = models.BooleanField() location = models.CharField(max_length=100); I've coded a python program called PageTree.py which allows me to request nodes from the database and manipulate the structure of the tree. Here is the trouble making method: def createPage(pageSource, pageName): page = Page() page.source = pageSource page.name = pageName page.save() return page I'm running this program in a shell through manage.py in Windows 7 manage.py shell from mysite.PageManager.models import Page, Source from mysite.PageManager.PageTree import * ... create someSource = Source(), populate the fields, and save it ... createPage(someSource, "test") ... NameError: global name 'source' is not defined When I type in the function definition for createPage into the shell by hand, the call works without error. This is driving me bonkers and help is appreciated.

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  • HTML/CSS: Keep the same height between the backgrounds of a term-description pair in a table-like de

    - by peroyomas
    I want to format a definition list in HTML as if it were a table with th in a column and td in another, with a background that alternates per row (although a background for the dt and another for the dd also fits for the problem), so I have this CSS: dl { font-family: Verdana, Geneva, sans-serif; font-size: 0.6em; overflow: hidden; width: 200px;; } dl dt { font-weight: bold; float: left; clear: left; padding-right: 1%; width: 48%; } dl dt:nth-of-type(odd), dl dd:nth-of-type(odd) { background-color: #EEE; } dl dt:nth-of-type(even), dl dd:nth-of-type(even) { background-color: #DDD; } dl dd { float: left; width: 50%; padding-left: 1%; margin-left: 0; } Example HTML: <dl> <dt>Key 1</dt> <dd>Value 1</dd> <dt>Very very very long key 2 </dt> <dd>Value 2</dd> <dt>Key 3</dt> <dd>Value 3 with<br /> line breaks</dd> <dt>Key 4</dt> <dd>Value 4</dd> </dl> The problem is that, due to the eventual height dissimilarity, "holes" with no background appears in the list: Is there a way to fix that?

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  • LINQ to SQL - Lightweight O/RM?

    - by CoffeeAddict
    I've heard from some that LINQ to SQL is good for lightweight apps. But then I see LINQ to SQL being used for Stackoverflow, and a bunch of other .coms I know (from interviewing with them). Ok, so is this true? for an e-commerce site that's bringing in millions and you're typically only doing basic CRUDs most the time with the exception of an occasional stored proc for something more complex, is LINQ to SQL complete enough and performance-wise good enough or able to be tweaked enough to run happily on an e-commerce site? I've heard that you just need to tweak performance on the DB side when using LINQ to SQL for a better approach. So there are really 2 questions here: 1) Meaning/scope/definition of a "Lightweight" O/RM solution: What the heck does "lightweight" mean when people say LINQ to SQL is a "lightweight O/RM" and is that true??? If this is so lightweight then why do I see a bunch of huge .coms using it? Is it good enough to run major .coms (obviously it looks like it is) and what determines what the context of "lightweight" is...it's such a generic statement. 2) Performance: I'm working on my own .com and researching different O/RMs. I'm not really looking at the Entity Framework (yet), just want to figure out the LINQ to SQL basics here and determine if it will be efficient enough for me. The problem I think is you can't tweak or control the SQL it generates...

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  • DLL Export C/C++ 6.00 function invoked by VB6

    - by nashth
    Hi all, I have been attemptng to create a DLL with C/C++ that can be accessed by VB6, and that's right I get error "453 Can't find DLL entry point myFunctionName in myDllName.dll" upon calling the function from a VB6 app. After searching the Web, including this site, I see that I am not alone, and I have tried the various solutions posted but error "453" is unexcapable. This is Not a COMM dll, and I believe that is possible when created via C/C++. In any case, please help, if you can. Please refer to the following simple test case below: The DLL created as a C/C++ 6.00 Win32 Dynamic-Link Library: #include // Note that I did try the line below rather than the def file, but to no avail... // #pragma comment(linker, "/EXPORT:ibask32=_ibask32@0") // Function definition extern "C" int __declspec(dllexport) __stdcall ibask32() { MessageBox(NULL,"String","Sample Code", NULL); return 0L; } The def file: LIBRARY "Gpib-32" EXPORTS ibask32 Now for the VB App: The following is the entire content of the startup Form1, Form_Load Option Explicit Private Sub Form_Load() Call ibask End Sub The following is a BAS module file that is added to the project: Option Explicit Declare Function ibask32 Lib "Gpib-32.dll" Alias "ibask" () As Long Sub ibask() Call ibask32 ' Note: This is the point of failure End Sub Thanks in advance if a workable solution can be provided, Tom

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  • How can I ignore the block content reading in Perl.

    - by Nano HE
    Hello. I plan to ignore the block content which include the start line of "MaterializeU4()" with the subroutin() read_block below. But failed. # Read a constant definition block from a file handle. # void return when there is no data left in the file. # Otherwise return an array ref containing lines to in the block. sub read_block { my $fh = shift; my @lines; my $block_started = 0; while( my $line = <$fh> ) { # how to correct my code below? I don't need the 2nd block content. $block_started++ if ( ($line =~ /^(status)/) && (index($line, "MaterializeU4") != 0) ) ; if( $block_started ) { last if $line =~ /^\s*$/; push @lines, $line; } } return \@lines if @lines; return; } Data as below: __DATA__ status DynTest = <dynamic 100> vid = 10002 name = "DynTest" units = "" status VIDNAME9000 = <U4 MaterializeU4()> vid = 9000 name = "VIDNAME9000" units = "degC" status DynTest = <U1 100> vid = 100 name = "Hello" units = "" Output: <StatusVariables> <SVID logicalName="DynTest" type="L" value="100" vid="10002" name="DynTest" units=""></SVID> <SVID logicalName="VIDNAME9000" type="L" value="MaterializeU4()" vid="9000" name="VIDNAME9000" units="degC"></SVID> <SVID logicalName="DynTest" type="L" value="100" vid="100" name="Hello" units=""></SVID> </StatusVariables> [Updated] I print the value of index($line, "MaterializeU4"), it output 25. Then I updated the code as below $block_started++ if ( ($line =~ /^(status)/) && (index($line, "MaterializeU4") != 25) Now it works. Any comments are welcome about my practice. Thank you.

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  • Python to C/C++ const char question

    - by tsukemonoki
    I am extending Python with some C++ code. One of the functions I'm using has the following signature: int PyArg_ParseTupleAndKeywords(PyObject *arg, PyObject *kwdict, char *format, char **kwlist, ...); (link: http://docs.python.org/release/1.5.2p2/ext/parseTupleAndKeywords.html) The parameter of interest is kwlist. In the link above, examples on how to use this function are given. In the examples, kwlist looks like: static char *kwlist[] = {"voltage", "state", "action", "type", NULL}; When I compile this using g++, I get the warning: warning: deprecated conversion from string constant to ‘char*’ So, I can change the static char* to a static const char*. Unfortunately, I can't change the Python code. So with this change, I get a different compilation error (can't convert char** to const char**). Based on what I've read here, I can turn on compiler flags to ignore the warning or I can cast each of the constant strings in the definition of kwlist to char *. Currently, I'm doing the latter. What are other solutions? Sorry if this question has been asked before. I'm new.

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  • If I cast an IQueryable as an IEnumerable then call a Linq extension method, which implementation gets called?

    - by James Morcom
    Considering the following code: IQueryable<T> queryable; // something to instantiate queryable var enumerable = (IEnumerable<T>) queryable; var filtered = enumerable.Where(i => i > 3); In the final line, which extension method gets called? Is it IEnumerable<T>.Where(...)? Or will IQueryable<T>.Where(...) be called because the actual implementation is still obviously a queryable? Presumably the ideal would be for the IQueryable version to be called, in the same way that normal polymorphism will always use the more specific override. In Visual Studio though when I right-click on the Where method and "Go to Definition" I'm taken to the IEnumerable version, which kind of makes sense from a visual point-of-view. My main concern is that if somewhere in my app I use Linq to NHibernate to get a Queryable, but I pass it around using an interface that uses the more general IEnumerable signature, I'll lose the wonders of deferred database execution!

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  • How does Haskell do pattern matching without us defining an Eq on our data types?

    - by devoured elysium
    I have defined a binary tree: data Tree = Null | Node Tree Int Tree and have implemented a function that'll yield the sum of the values of all its nodes: sumOfValues :: Tree -> Int sumOfValues Null = 0 sumOfValues (Node Null v Null) = v sumOfValues (Node Null v t2) = v + (sumOfValues t2) sumOfValues (Node t1 v Null) = v + (sumOfValues t1) sumOfValues (Node t1 v t2) = v + (sumOfValues t1) + (sumOfValues t2) It works as expected. I had the idea of also trying to implement it using guards: sumOfValues2 :: Tree -> Int sumOfValues2 Null = 0 sumOfValues2 (Node t1 v t2) | t1 == Null && t2 == Null = v | t1 == Null = v + (sumOfValues2 t2) | t2 == Null = v + (sumOfValues2 t1) | otherwise = v + (sumOfValues2 t1) + (sumOfValues2 t2) but this one doesn't work because I haven't implemented Eq, I believe: No instance for (Eq Tree) arising from a use of `==' at zzz3.hs:13:3-12 Possible fix: add an instance declaration for (Eq Tree) In the first argument of `(&&)', namely `t1 == Null' In the expression: t1 == Null && t2 == Null In a stmt of a pattern guard for the definition of `sumOfValues2': t1 == Null && t2 == Null The question that has to be made, then, is how can Haskell make pattern matching without knowing when a passed argument matches, without resorting to Eq?

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  • MySQL Join/Comparison on a DATETIME column (<5.6.4 and > 5.6.4)

    - by Simon
    Suppose i have two tables like so: Events ID (PK int autoInc), Time (datetime), Caption (varchar) Position ID (PK int autoinc), Time (datetime), Easting (float), Northing (float) Is it safe to, for example, list all the events and their position if I am using the Time field as my joining criteria? I.e.: SELECT E.*,P.* FROM Events E JOIN Position P ON E.Time = P.Time OR, even just simply comparing a datetime value (taking into consideration that the parameterized value may contain the fractional seconds part - which MySQL has always accepted) e.g. SELECT E.* FROM Events E WHERE E.Time = @Time I understand MySQL (before version 5.6.4) only stores datetime fields WITHOUT milliseconds. So I would assume this query would function OK. However as of version 5.6.4, I have read MySQL can now store milliseconds with the datetime field. Assuming datetime values are inserted using functions such as NOW(), the milliseconds are truncated (<5.6.4) which I would assume allow the above query to work. However, with version 5.6.4 and later, this could potentially NOT work. I am, and only ever will be interested in second accuracy. If anyone could answer the following questions would be greatly appreciated: In General, how does MySQL compare datetime fields against one another (consider the above query). Is the above query fine, and does it make use of indexes on the time fields? (MySQL < 5.6.4) Is there any way to exclude milliseconds? I.e. when inserting and in conditional joins/selects etc? (MySQL 5.6.4) Will the join query above work? (MySQL 5.6.4) EDIT I know i can cast the datetimes, thanks for those that answered, but i'm trying to tackle the root of the problem here (the fact that the storage type/definition has been changed) and i DO NOT want to use functions in my queries. This negates all my work of optimizing queries applying indexes etc, not to mention having to rewrite all my queries. EDIT2 Can anyone out there suggest a reason NOT to join on a DATETIME field using second accuracy?

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  • Options for organizing android app with multiple independent apps

    - by lazyguy
    Problem Definition: We have a fairly large app which has multiple use cases such that they are all independent of each other. For example lets say we have a1, a2, a3 & a4 modules that are independent apps or use cases for our main app 'A'. The independent a1, a2, a3, a4 are all purchasable apps such that the user goes to our website instead of play store and activate either a1 or a2 by paying some fees on our website. So basically App 'A' is a free app in play-store and is sort of Dashboard with buttons to launch a1, a2, a3, a4. When the user click on lets say a1 button then we will check if a1 is already installed and launch it but if it is not present then give the user a link to download it. Option 1: Have a main app 'A' and a1, a2, a3, a4 as library project. But with this approach the main app A is too big in size. Option 2: Have a1, a2, a3, a4 build as separate .apk and then put in the assets folder of main app 'A' and then install them as needed. Again size of main app A is bigger. Option 3: Upload a1, a2, a3, a4 to a third party website or play store and download from it as needed. This way the main app remains lighter. Observation: In all these approaches there will be an independent app installed with its own icon on users phone. So basically user can launch from either the Dashboard (which will eventually launch an intent from Activity in a1 app) or user can directly launch app a1. Follow-up Question: Is there any other solution that anyone can suggest to tackle this kind of problem? Another things is by going this approach app a1, a2, a3, a4 can be developed & tested independently of each other.

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  • Java Generics error when implementing Hibernate message interpolator

    - by Jayaprakash
    Framework: Spring, Hibernate. O/S: Windows I am trying to implement hibernate's Custom message interpolator following the direction of this Link. When implementing the below class, it gives an error "Cannot make a static reference to the non-static type Locale". public class ClientLocaleThreadLocal<Locale> { private static ThreadLocal tLocal = new ThreadLocal(); public static void set(Locale locale) { tLocal.set(locale); } public static Locale get() { return tLocal.get(); } public static void remove() { tLocal.remove(); } } As I do not know generics enough, not sure how is being used by TimeFilter class below and the purpose of definition in the above class. public class TimerFilter implements Filter { public void destroy() { } public void doFilter(ServletRequest req, ServletResponse res, FilterChain filterChain) throws IOException, ServletException { try { ClientLocaleThreadLocal.set(req.getLocale()); filterChain.doFilter(req, res); }finally { ClientLocaleThreadLocal.remove(); } } public void init(FilterConfig arg0) throws ServletException { } } Will doing the following be okay? Change static method/field in ClientLocaleThreadLocal to non-static method/fields In TimeFilter, set locale by instantiating new object as below. new ClientLocaleThreadLocal().set(req.getLocale()) Thanks for your help in advance

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  • Design issue when having classes implement different interfaces to restrict client actions

    - by devoured elysium
    Let's say I'm defining a game class that implements two different views: interface IPlayerView { void play(); } interface IDealerView { void deal(); } The view that a game sees when playing the game, and a view that the dealer sees when dealing the game (this is, a player can't make dealer actions and a dealer can't make player actions). The game definition is as following: class Game : IPlayerView, IDealerView { void play() { ... } void deal() { ... } } Now assume I want to make it possible for the players to play the game, but not to deal it. My original idea was that instead of having public Game GetGame() { ... } I'd have something like public IPlayerView GetGame() { ... } But after some tests I realized that if I later try this code, it works: IDealerView dealerView = (IDealerView)GameClass.GetGame(); this works as lets the user act as the dealer. Am I worrying to much? How do you usually deal with this patterns? I could instead make two different classes, maybe a "main" class, the dealer class, that would act as factory of player classes. That way I could control exactly what I would like to pass on the the public. On the other hand, that turns everything a bit more complex than with this original design. Thanks

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  • Confusion with a while statement evaluating if a number is triangular

    - by Darkkurama
    I've been having troubles trying to figure out how to solve a function. I've been assigned the development of a little programme which tells if a number is "triangular" (a number is triangular when the addition of certain consecutive numbers in the [1,n] interval is n. Following the definition, the number 10 is triangular, because in the [1,10] interval, 1+2+3+4=10). I've coded this so far: class TriangularNumber{ boolean numTriangular(int n) { boolean triangular = false; int i = n; while(n>=0 && triangular){ //UE06 is a class which contains the function "f0", which makes the addition of all the numbers in a determined interval UE06 p = new UE06(); if ((p.f0(1, i))==n) triangular = true; else i=i-1; } return triangular; } boolean testTriangular = numTriangular(10) == true && numTriangular(7) == false && numTriangular(6) == true; public static void main(String[] args){ TriangularNumber p = new TriangularNumber(); System.out.println("testTriangular = " + p.testTriangular); } } According to those boolean tests I made, the function is wrong. As I see the function, it goes like this: I state that the input number in the initial state isn't triangular (triangular=false) and i=n (determining the interval [1,i] where the function is going to be evaluated While n is greater or equals 0 and the number isn't triangular, the loop starts The loop goes like this: if the addition of all the numbers in the [1,i] interval is n, the number is triangular, causing the loop to end. If that statement is false, i goes from i to (i-1), starting the loop again with that particular interval, and so on till the addition is n. I can't spot the error in my "algorithm", any advice? Thanks!

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  • Error using maven profiles

    - by user3127896
    I've added two profiles to my application and that how it looks: <profiles> <profile> <id>dev</id> <properties> <db.username>root</db.username> <db.password>root</db.password> <db.connectionURL>localhost:3306</db.connectionURL> <db.driverClass>com.mysql.jdbc.Driver</db.driverClass> </properties> </profile> <profile> <id>prod</id> <properties> <db.username>prodroot</db.username> <db.password>prodpass</db.password> <db.connectionURL>localhost:3306</db.connectionURL> <db.driverClass>com.mysql.jdbc.Driver</db.driverClass> </properties> </profile> </profiles> In my jdbc.properties file i changed values like this: jdbc.driverClassName=${db.driverClass} jdbc.dialect=org.hibernate.dialect.MySQLDialect jdbc.databaseurl=jdbc:mysql://${db.connectionURL}/dbname jdbc.username=${db.username} jdbc.password=${db.password} And here's bean from spring-container.xml <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close" p:driverClassName="${jdbc.driverClassName}" p:url="${jdbc.databaseurl}" p:username="${jdbc.username}" p:password="${jdbc.password}" /> When i try to deploy my application i got following error: SEVERE: Exception sending context initialized event to listener instance of class org.springframework.web.context.ContextLoaderListener org.springframework.beans.factory.BeanDefinitionStoreException: Invalid bean definition with name 'dataSource' defined in ServletContext resource [/WEB-INF/spring-servlet.xml]: Could not resolve placeholder 'db.driverClass' Structure of project: Any ideas what i'm doing wrong? Thanks in advance!

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  • Importing a C DLL's functions into a C++ program

    - by bobobobo
    I have a 3rd party library that's written in C. It exports all of its functions to a DLL. I have the .h file, and I'm trying to load the DLL from my C++ program. The first thing I tried was surrounding the parts where I #include the 3rd party lib in #ifdef __cplusplus extern "C" { #endif and, at the end #ifdef __cplusplus } // extern "C" #endif But the problem there was, all of the DLL file function linkage looked like this in their header files: a_function = (void *)GetProcAddress(dll, "a_function"); While really a_function had type int (*a_function) (int *). Apparently MSVC++ compiler doesn't like this, while MSVC compiler does not seem to mind. So I went through (brutal torture) and fixed them all to the pattern typedef int (*_a_function) (int *); _a_function a_function ; Then, to link it to the DLL code, in main(): a_function = (_a_function)GetProcAddress(dll, "a_function"); This SEEMS to make the compiler MUCH, MUCH happier, but it STILL complains with this final set of 143 errors, each saying for each of the DLL link attempts: error LNK2005: _a_function already defined in main.obj main.obj Multiple symbol definition errors.. sounds like a job for extern! SO I went and made ALL the function pointer declarations as follows: function_pointers.h typedef int (*_a_function) (int *); extern _a_function a_function ; And in a cpp file: function_pointers.cpp #include "function_pointers.h" _a_function a_function ; ALL fine and dandy.. except for linker errors now of the form: error LNK2001: unresolved external symbol _a_function main.obj Main.cpp includes "function_pointers.h", so it should know where to find each of the functions.. I am bamboozled. Does any one have any pointers to get me functional? (Pardon the pun..)

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  • How can I write a function template for all types with a particular type trait?

    - by TC
    Consider the following example: struct Scanner { template <typename T> T get(); }; template <> string Scanner::get() { return string("string"); } template <> int Scanner::get() { return 10; } int main() { Scanner scanner; string s = scanner.get<string>(); int i = scanner.get<int>(); } The Scanner class is used to extract tokens from some source. The above code works fine, but fails when I try to get other integral types like a char or an unsigned int. The code to read these types is exactly the same as the code to read an int. I could just duplicate the code for all other integral types I'd like to read, but I'd rather define one function template for all integral types. I've tried the following: struct Scanner { template <typename T> typename enable_if<boost::is_integral<T>, T>::type get(); }; Which works like a charm, but I am unsure how to get Scanner::get<string>() to function again. So, how can I write code so that I can do scanner.get<string>() and scanner.get<any integral type>() and have a single definition to read all integral types? Update: bonus question: What if I want to accept more than one range of classes based on some traits? For example: how should I approach this problem if I want to have three get functions that accept (i) integral types (ii) floating point types (iii) strings, respectively.

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  • in haskell, why do I need to specify type constraints, why can't the compiler figure them out?

    - by Steve
    Consider the function, add a b = a + b This works: *Main> add 1 2 3 However, if I add a type signature specifying that I want to add things of the same type: add :: a -> a -> a add a b = a + b I get an error: test.hs:3:10: Could not deduce (Num a) from the context () arising from a use of `+' at test.hs:3:10-14 Possible fix: add (Num a) to the context of the type signature for `add' In the expression: a + b In the definition of `add': add a b = a + b So GHC clearly can deduce that I need the Num type constraint, since it just told me: add :: Num a => a -> a -> a add a b = a + b Works. Why does GHC require me to add the type constraint? If I'm doing generic programming, why can't it just work for anything that knows how to use the + operator? In C++ template programming, you can do this easily: #include <string> #include <cstdio> using namespace std; template<typename T> T add(T a, T b) { return a + b; } int main() { printf("%d, %f, %s\n", add(1, 2), add(1.0, 3.4), add(string("foo"), string("bar")).c_str()); return 0; } The compiler figures out the types of the arguments to add and generates a version of the function for that type. There seems to be a fundamental difference in Haskell's approach, can you describe it, and discuss the trade-offs? It seems to me like it would be resolved if GHC simply filled in the type constraint for me, since it obviously decided it was needed. Still, why the type constraint at all? Why not just compile successfully as long as the function is only used in a valid context where the arguments are in Num? Thank you.

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  • Interpretation of int (*a)[3]

    - by kapuzineralex
    When working with arrays and pointers in C, one quickly discovers that they are by no means equivalent although it might seem so at a first glance. I know about the differences in L-values and R-values. Still, recently I tried to find out the type of a pointer that I could use in conjunction with a two-dimensional array, i.e. int foo[2][3]; int (*a)[3] = foo; However, I just can't find out how the compiler "understands" the type definition of a in spite of the regular operator precedence rules for * and []. If instead I were to use a typedef, the problem becomes significantly simpler: int foo[2][3]; typedef int my_t[3]; my_t *a = foo; At the bottom line, can someone answer me the questions as to how the term int (*a)[3] is read by the compiler? int a[3] is simple, int *a[3] is simple as well. But then, why is it not int *(a[3])? EDIT: Of course, instead of "typecast" I meant "typedef" (it was just a typo).

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  • C++ template and pointers

    - by Kary
    I have a problem with a template and pointers ( I think ). Below is the part of my code: /* ItemCollection.h */ #ifndef ITEMCOLLECTION_H #define ITEMCOLLECTION_H #include <cstddef> using namespace std; template <class T> class ItemCollection { public: // constructor //destructor void insertItem( const T ); private: struct Item { T price; Item* left; Item* right; }; Item* root; Item* insert( T, Item* ); }; #endif And the file with function defintion: /* ItemCollectionTemp.h-member functions defintion */ #include <iostream> #include <cstddef> #include "ItemCollection.h" template <class Type> Item* ItemCollection <T>::insert( T p, Item* ptr) { // function body } Here are the errors which are generated by this line of code: Item* ItemCollection <T>::insert( T p, Item* ptr) Errors: error C2143: syntax error : missing ';' before '*' error C4430: missing type specifier - int assumed. Note: C++ does not support default-int error C2065: 'Type' : undeclared identifier error C2065: 'Type' : undeclared identifier error C2146: syntax error : missing ')' before identifier 'p' error C4430: missing type specifier - int assumed. Note: C++ does not support default-int error C2470: 'ItemCollection::insert' : looks like a function definition, but there is no parameter list; skipping apparent body error C2072: 'ItemCollection::insert': initialization of a function error C2059: syntax error : ')' Any help is much appreciated.

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  • Mysql dropping inserts with triggers

    - by user2891127
    Using mysql 5.5. I have two tables. One has a whitelist of hashes. When I insert a new row into the other table, I want to first compare the hash in the insert statement to the whitelist. If it's in the whitelist, I don't want to do the insert (less data to plow through later). The inserts are generated from another program and are text files with sql statements. I've been playing with triggers, and almost have it working: BEGIN IF (select count(md5hash) from whitelist where md5hash=new.md5hash) 0 THEN SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'Already Whitelisted'; END IF; END But there's a problem. The Signal throwing up the error stops the import. I want to skip that line, not stop the whole import. Some searching didn't find any way to silently skip the import. My next idea was to create a duplicate table definition, and redirect the insert to that dup table. But the old and new don't seem to apply to table names. Other then adding an ignore column to my table then doing a mass drop based on that column after the import, is there any way to achieve my goal?

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  • Holding variables in memory, C++

    - by b-gen-jack-o-neill
    Today something strange came to my mind. When I want to hold some string in C (C++) the old way, without using string header, I just create array and store that string into it. But, I read that any variable definition in C in local scope of function ends up in pushing these values onto the stack. So, the string is actually 2* bigger than needed. Because first, the push instructions are located in memory, but then when they are executed (pushed onto the stack) another "copy" of the string is created. First the push instructions, than the stack space is used for one string. So, why is it this way? Why doesn't compiler just add the string (or other variables) to the program instead of creating them once again when executed? Yes, I know you cannot just have some data inside program block, but it could just be attached to the end of the program, with some jump instruction before. And than, we would just point to these data? Because they are stored in RAM when the program is executed. Thanks.

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