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  • C++ private pointer "leaking"?

    - by jbu
    I'm going to create a class to hold a long list of parameters that will be passed to a function. Let's use this shorter example: class ParamList{ public: ParamList(string& a_string); string& getString(); //returns my_string private: string& my_string; } My question is this: my_string is private, yet I'm returning the reference to it. Isn't that called something like private pointer leaking in C++? Is this not good programming practice? I want callers of getString to be able to get the reference and also modify it. Please let me know. Thanks, jbu edit1: callers will use getString() and modify the string that was returned.

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  • using dummy row with NOT NULL to solve DEFAUT NULL

    - by Tony38
    I know having DEFAULT NULLS is not a good practice but I have many optional lookup values which are FK in the system so to solve this issue here is what i am doing: I use NOT NULL for every FK / lookup valve field. I have the first row in every table which is PK id = 1 as a dummy row with just "none" in all the columns. this way I can use NOT NULL in my schema and if needed reference to the none row values which should be null. Is this a good design or any other work arounds?

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  • rails belongs_to sql statement using NULL id

    - by Team Pannous
    When paginating through our Phrase table it takes very long to return the results. In the sql logs we see many sql requests which don't make sense to us: Phrase Load (7.4ms) SELECT "phrases".* FROM "phrases" WHERE "phrases"."id" IS NULL LIMIT 1 User Load (0.4ms) SELECT "users".* FROM "users" WHERE "users"."id" IS NULL LIMIT 1 These add up significantly. Is there a way to prevent querying against null ids? This is the underlying model: class Phrase < ActiveRecord::Base belongs_to :user belongs_to :response, :class_name => "Phrase", :foreign_key => "next_id" end

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  • C++ pointer, Beginner Question...

    - by BobAlmond
    Hi there, just want to ask a beginner question... here, I made some code, for understanding the concept/basic of pointer: int a=1; int *b=&a; int **c = &b; int ***d = &c; cout << &*(&*d) << endl; can someone explain to me, why the &*(&d) return address of "c" instead of address of "b"? I've also tried code like &(&(&(&*(&*d)))), but it keep return address of "c" Thanks a lot :)

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  • C++ pointer to functions, Beginner Question...

    - by BobAlmond
    Hi all, I want to ask about pointer in C++ I have some simple code: int add(int a, int b){ return a+b; } int runner(int x,int y, int (*functocall)(int, int)){ return (*functocall)(x,y); } now, suppose I call those functions using this way : cout<<runner(2,5,&add); or maybe cout<<runner(2,5,add); is there any difference? because when I tried, the result is the same and with no error. Thanks a lot

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  • Is apparent NULL pointer dereference in C actually pointer arithmetic?

    - by karthik A
    hey ive got this piece of code. It dereferences a null pointer here. But then there is an and with unsigned int. I really dont understand the whole part. Can someone explain the output.?? struct hi { long a; int b; long c; }; int main() { struct hi ob={3,4,5}; struct hi *ptr=&ob; int num= (unsigned int) & (((struct hi *)0)->b); printf("%d",num); printf("%d",*(int *)((char *)ptr + (unsigned int) & (((struct hi *)0)->b))); } The output I get is 44. But how does it work?

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  • Is there an "opposite" to the null coalescing operator? (…in any language?)

    - by Jay
    null coalescing translates roughly to return x, unless it is null, in which case return y I often need return null if x is null, otherwise return x.y I can use return x == null ? null : x.y; Not bad, but that null in the middle always bothers me -- it seems superfluous. I'd prefer something like return x :: x.y;, where what follows the :: is evaluated only if what precedes it is not null. I see this as almost an opposite to null coalescence, kind of mixed in with a terse, inline null-check, but I'm [almost] certain that there is no such operator in C#. Are there other languages that have such an operator? If so, what is it called? (I know that I can write a method for it in C#; I use return NullOrValue.of(x, () => x.y);, but if you have anything better, I'd like to see that too.)

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  • A null value should be considered as 0 when addition of it is done with decimal value.

    - by Harikrishna
    There are three column in the datatable A,B and C. Now each column is type of decimal. Now I am doing like dt.Columns["A"].Expression="B+C"; to make addition of Column B's record and column C's record. Now if there is any value of B or C is null then addition of B and C will be null like B's value is 3 and C's value is null for first row then B+C(3+null) will be null which is not appropriate, the result of addition should be 3.If I replace 0 instead of null then it will be ok.But whereever there is null value in the records it should be remain it is and it should not be replaced by 0.That is null value should not be replaced by 0 and when addition of null value is done with any decimal value null value should be considered as 0. Is it possible,how can we do this ?

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  • Modifying a const through a non-const pointer

    - by jasonline
    I'm a bit confused what happened in the following code: const int e = 2; int* w = ( int* ) &e; // (1) cast to remove const-ness *w = 5; // (2) cout << *w << endl; // (3) outputs 5 cout << e << endl; // (4) outputs 2 cout << "w = " << w << endl; // (5) w points to the address of e cout << "&e = " << &e << endl; In (1), w points to the address of e. In (2), that value was changed to 5. However, when the values of *w and e were displayed, their values are different. But if you print value of w pointer and &e, they have the same value/address. How come e still contained 2, even if it was changed to 5? Were they stored in a separate location? Or a temporary? But how come the value pointed by w is still the address of e?

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  • Go: using a pointer to array

    - by Sean
    I'm having a little play with google's Go language, and I've run into something which is fairly basic in C but doesn't seem to be covered in the documentation I've seen so far When I pass a pointer to an array to a function, I presumed we'd have some way to access it as follows: func conv(x []int, xlen int, h []int, hlen int, y *[]int) for i := 0; i<xlen; i++ { for j := 0; j<hlen; j++ { *y[i+j] += x[i]*h[j] } } } But the Go compiler doesn't like this: sean@spray:~/dev$ 8g broke.go broke.go:8: invalid operation: y[i + j] (index of type *[]int) Fair enough - it was just a guess. I have got a fairly straightforward workaround: func conv(x []int, xlen int, h []int, hlen int, y_ *[]int) { y := *y_ for i := 0; i<xlen; i++ { for j := 0; j<hlen; j++ { y[i+j] += x[i]*h[j] } } } But surely there's a better way. The annoying thing is that googling for info on Go isn't very useful as all sorts of C\C++\unrelated results appear for most search terms.

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  • vector::erase with pointer member

    - by matt
    I am manipulating vectors of objects defined as follow: class Hyp{ public: int x; int y; double wFactor; double hFactor; char shapeNum; double* visibleShape; int xmin, xmax, ymin, ymax; Hyp(int xx, int yy, double ww, double hh, char s): x(xx), y(yy), wFactor(ww), hFactor(hh), shapeNum(s) {visibleShape=0;shapeNum=-1;}; //Copy constructor necessary for support of vector::push_back() with visibleShape Hyp(const Hyp &other) { x = other.x; y = other.y; wFactor = other.wFactor; hFactor = other.hFactor; shapeNum = other.shapeNum; xmin = other.xmin; xmax = other.xmax; ymin = other.ymin; ymax = other.ymax; int visShapeSize = (xmax-xmin+1)*(ymax-ymin+1); visibleShape = new double[visShapeSize]; for (int ind=0; ind<visShapeSize; ind++) { visibleShape[ind] = other.visibleShape[ind]; } }; ~Hyp(){delete[] visibleShape;}; }; When I create a Hyp object, allocate/write memory to visibleShape and add the object to a vector with vector::push_back, everything works as expected: the data pointed by visibleShape is copied using the copy-constructor. But when I use vector::erase to remove a Hyp from the vector, the other elements are moved correctly EXCEPT the pointer members visibleShape that are now pointing to wrong addresses! How to avoid this problem? Am I missing something?

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  • Can PCRE regex match a null character?

    - by Keng
    I have a text source with nulls in it and I need to pull them out along with my regex pattern. Can regex even match a null character? I only realized I had them when my pattern refused to match and when I pasted it into Notepad++ it showed all the null characters.

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  • Mysql Left Join Null Result

    - by Ozzy
    I have this query SELECT articles.*, users.username AS `user` FROM `articles` LEFT JOIN `users` ON articles.user_id = users.id ORDER BY articles.timestamp Basically it returns the list of articles and the username that the article is associated to. Now if there is no entry in the users table for a particular user id, the users var is NULL. Is there anyway to make it that if its null it returns something like "User Not Found"? or would i have to do this using php?

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  • Can a constructor return a NULL value?

    - by Sanctus2099
    I know constructors don't "return" anything but for instance if I call CMyClass *object = new CMyClass() is there any way to make object to be NULL if the constructor fails? In my case I have some images that have to be loaded and if the file reading fails I'd like it to return null. Is there any way to do that? Thanks in advance.

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  • Checking for a null int value from a Java ResultSet

    - by ian_scho_es
    In Java I'm trying to test for a null value, from a ResultSet, where the column is being cast to a primitive int type. int iVal; ResultSet rs = magicallyAppearingStmt.executeQuery(query); if (rs.next()) { if (rs.getObject("ID_PARENT") != null && !rs.wasNull()) { iVal = rs.getInt("ID_PARENT"); } } From the code fragment above, is there a better way to do this, and I assume that the second wasNull() test is redundant? Educate us, and Thanks

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  • Is null a class in java?

    - by Somerandomeguy
    According to, http://www.freshvanilla.org:8080/display/www/Java+Interview+Questions Under, Which class is the superclass of every class? null seems to be the answer. I found that new Object().getClass().getSuperClass() verifies the answer as correct. But can null be considered a class? I see all primitive data types are represented as Class objects from java[dot]sun.com/j2se/1.4.2/docs/api/java/lang/Class.html

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  • Android ListView: getTag() returns null

    - by TianDong
    Hallo all, I have a ListView which contains a Button in each line. The following code is part of the getView() Method public View getView(final int position, View convertView, ViewGroup parent) { View row = convertView; TextView tv; Button saveA_button; EditText edittext; FITB_ViewWrapper wrapper; if (row == null) { LayoutInflater li = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE); if (ChooseMode_Act.modeInfo.equalsIgnoreCase("Training")) { row = li.inflate(R.layout.exercise_for_training_fitb,parent, false); }else { row = li.inflate(R.layout.exercise_for_exam_fitb,parent, false); } wrapper=new FITB_ViewWrapper(row); row.setTag(wrapper); if (ChooseMode_Act.modeInfo.equalsIgnoreCase("Exam")) { saveA_button=wrapper.getSaveAnswer_Button(); OnClickListener l=new OnClickListener() { @Override public void onClick(View v) { Integer mp=(Integer)v.getTag(); Log.i("mp","my Position is: "+mp); } }; saveA_button.setOnClickListener(l); } }else { wrapper=(FITB_ViewWrapper) row.getTag(); } For my App i need to known to which item the Button belongs to, so i try to detect it. The code Log.i("mp","my Position is: "+mp); puts out a message: mp myPosition is: null I can't understand, why do i get a "null" but not an Integer? How can i find out the Position of an Item in a ListView? Thanks a lot.

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  • Erlang ODBC parameter query with null parameters

    - by Schlomer
    Is it possible to pass null values to parameter queries? For example Sql = "insert into TableX values (?,?)". Params = [{sql_integer, [Val1]}, {sql_float, [Val2]}]. % Val2 may be a float, or it may be the atom, undefined odbc:param_query(OdbcRef, Sql, Params). Now, of course odbc:param_query/3 is going to complain if Val2 is undefined when trying to match to a sql_float, but my question is... Is it possible to use a parameterized query, such as: Sql = "insert into TableY values (?,?,?,?,?,?,?,?,?)". with any null parameters? I have a use case where I am dumping a large number of real-time data into a database by either inserting or updating. Some of the tables I am updating have a dozen or so nullable fields, and I do not have a guarantee that all of the data will be there. Concatenating a SQL together for each query, checking for null values seems complex, and the wrong way to do it. Having a parameterized query for each permutation is simply not an option. Any thoughts or ideas would be fantastic! Thank you!

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  • wave.getState() returns null

    - by RMorrisey
    When trying to call wave.getState() in my Google Wave gadget, I get back null (no state object). How can I initialize the Wave state object? I am working in the Wave Sandbox. My ModulePrefs contains the following: <Require feature="wave" /> <Require feature="rpc"/> I got the "rpc" feature from some google groups post when searching for a fix, but it doesn't seem to be any help. The gadget contains a jQuery plugin, which defines the classes I use (not shown), attaches an event handler to the link that shows up in edit mode, and sets up the callback methods with the google wave gadget initializer: $.fn.extend({ $.gork.InitPass.newButtonClick = function newButtonClick() { var jer = new $.gork.InitPass.Player('Jeremias', 12, 2); var delta = {}; delta[jer.name] = jer.serialize(); wave.getState().submitDelta(delta); }; $.gork.InitPass.modeCallback = function modeCallback() { var state = wave.getState(); var mode = wave.getMode(); $.gork.InitPass.getContainer().ipCombatState(state, (mode == wave.Mode.EDIT)); }; $.gork.InitPass.stateCallback = function stateCallback() { $.gork.InitPass.getContainer().ipCombatState( wave.getState(), (wave.getMode() == wave.Mode.EDIT)); alert('state'); }; $.gork.InitPass.init = function init() { if (wave && wave.isInWaveContainer()) { var mode = wave.getMode(); $('.gork-ip-container').ipCombatState(null, (mode == wave.Mode.EDIT)); wave.setModeCallback($.gork.InitPass.modeCallback); wave.setStateCallback($.gork.InitPass.stateCallback); } }; })(jQuery); gadgets.util.registerOnLoadHandler($.gork.InitPass.init); $(function ready() { $.gork.InitPass.getContainer().find('.gork-ip-edit .addSection a.newButton').click( $.gork.InitPass.newButtonClick); }); So there are two main pieces of functionality here: When the mode changes, ipCombatState(...) is called. This changes the visual appearance of the gadget when the user puts the gadget in Edit mode (CTRL+E), by hiding the view DIV and displaying the edit DIV. The newButtonClick callback (which is attached to the link "a.newButton" in the edit container) is supposed to add Jeremias (Nate's Shadowrun character) to the gadget state, so that he'll be appear as a table row in edit mode. I have verified that the initializer method is called, and the view/edit mode switch works just fine (except the state is null). When I click on the new button link (the link at the bottom in edit mode), and trigger the newButtonClick handler, I get an error because wave.getState() also returns null. How can I initialize the wave state so that I can work with it? The purpose of my gadget will be to keep track of combat initiative order in a Shadowrun tabletop game (4th Ed). You can test it out in Wave and see what I have so far: http://gorkwobble.herobo.com/wave/init-pass.xml The actual javascript code is externalized to: http://gorkwobble.herobo.com/wave/init-pass.js P.S. If any Shadowrun players read this, and want to hear about it when I get the gadget working, leave a comment and I'll wave you.

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