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• fprintf() within a subprogram

  - by sergio

  Im stuck when trying to write to my file within my subprogram. void new_page(float *a, float *b, float *c, int *d){ fprintf(results,"\nPage Totals: %f\t%f\t%f\t%d", *a,*b,*c,*d); } I get a warning saying "Warning: incompatible implicit declaration of built-in function 'fprinf' [enabled by default]" "error: 'results' undeclared (first use in this function)" in main fprintf works fine, its just when it comes to the subprogram/function it wont work. from my understanding it thinks that results is undeclared, so do i have to pass the name or location of the file to make it work?

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• WPF: Hidden parent and visible child

  - by oakskc

  As of last night, I decided to start learning about WPF and have been reading through a number of online tutorials and books. This is a huge shift. One feature that has fascinated me is the implicit property value inheritance. I know in the WinForms world, if a control is not visible then neither are any of the child controls. Same seems to be true in the WPF world, as expected. I wondered if explicitly setting the child control's Visibility property would allow for an invisible parent and visible child and it did not. Is this something that would be possible in WPF? Can you have a container control that is hidden with visible children? This is more an exercise of curiosity than anything. I'm still trying to wrap my head around a lot of what I've been reading.

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• floating constants in C

  - by Daziplqa

  Hi floks, I have a question concerning floating constants in C. In Java, the default type of floating point constants in double, so the following will causes a compilation error in java: float f = 100.0; // we either need to uses type case operator or put f at the end of the number constant. This is because the default floating-point constants are of type double and casting from double to float without type cast operator is an error, so we need either add a type case operator or put f at the end of the number. So, Why in C this doesn't produce an error, Is it because the default floating-point constants are of type float, or because the compiler do an implicit down-cast conversion (that doesn't requires type case operator in C)????

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• Fixing "Lock wait timeout exceeded; try restarting transaction" for a 'stuck" Mysql table?

  - by Tom

  From a script I sent a query like this thousands of times to my local database: update some_table set some_column = some_value I forgot to add the where part, so the same column was set to the same a value for all the rows in the table and this was done thousands of times and the column was indexed, so the corresponding index was probably updated too lots of times. I noticed something was wrong, because it took too long, so I killed the script. I even rebooted my computer since them, but something stuck in the table, because simple queries take a very long time to run and when I try dropping the relevant index it fails with this message: Lock wait timeout exceeded; try restarting transaction It's an innodb table, so stuck the transaction is probably implicit. How can I fix this table and remove the stuck transaction from it?

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• Can I use memcpy in C++ to copy classes that have no pointers or virtual functions

  - by Shane MacLaughlin

  Say I have a class, something like the following; class MyClass { public: MyClass(); int a,b,c; double x,y,z; }; #define PageSize 1000000 MyClass Array1[PageSize],Array2[PageSize]; If my class has not pointers or virtual methods, is it safe to use the following? memcpy(Array1,Array2,PageSize*sizeof(MyClass)); The reason I ask, is that I'm dealing with very large collections of paged data, as decribed here, where performance is critical, and memcpy offers significant performance advantages over iterative assignment. I suspect it should be ok, as the 'this' pointer is an implicit parameter rather than anything stored, but are there any other hidden nasties I should be aware of?

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• What are the other new features of C# 4.0, after dynamic and optional parameters?

  - by Abel

  So, C# 4.0 came out yesterday. It introduced the much-debated dynamic keyword, named and optional parameters. Smaller improvements were the implicit ref and recognizing of indexed and default properties on COM methods, contra- and co-variance (really a .NET CLR feature, not C# only) and... Is that really it? Are dynamic and optional/named params the only real improvements to C#? Or did I miss something? Not that I'm complaining, but it seems a bit meager after C# 2.0 (generics) and C# 3.0 (lambda, LINQ). Maybe the language just reached actual maturity?

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• How cast in c#/.net 3.5 works? for types with '?'

  - by Inez

  This is my code which works public decimal? Get() { var res = ... return res.Count() > 0 ? res.First() : (decimal?) null; } and this one doesn't work public decimal? Get() { var res = ... return res.Count() > 0 ? res.First() : null; } giving the compilator error: Error 1 Type of conditional expression cannot be determined because there is no implicit conversion between 'decimal' and '' I wonder why? any ideas?

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• What is the difference between IEditableObject and IRevertibleChangeTracking?

  - by open-collar

  What is the difference between IEditableObject and IRevertibleChangeTracking (both from the System.ComponentModel namespace)? It looks as if the first supports explicit transaction whilst the second is more implicit - but the net result is the same. How should I go about implementing this in code? At the moment I do nothing in BeginEdit and call RejectChanges and AcceptChanges in EndEdit and CancelEdit respectively. My problem is that this will also accept the changes made prior to the BeginEdit. Is that really what MS wanted or am I trying to implement two mutually exclusive interfaces?

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• How does cast in C#/.NET 3.5 work for types with '?'

  - by Inez

  This is my code which works public decimal? Get() { var res = ... return res.Count() > 0 ? res.First() : (decimal?) null; } and this one doesn't work public decimal? Get() { var res = ... return res.Count() > 0 ? res.First() : null; } giving the compiler error: Error 1 Type of conditional expression cannot be determined because there is no implicit conversion between 'decimal' and '<null>' I wonder why? any ideas?

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• make a lazy var in scala

  - by ayvango

  Scala does not permit to create laze vars, only lazy vals. It make sense. But I've bumped on use case, where I'd like to have similar capability. I need a lazy variable holder. It may be assigned a value that should be calculated by time-consuming algorithm. But it may be later reassigned to another value and I'd like not to call first value calculation at all. Example assuming there is some magic var definition lazy var value : Int = _ val calc1 : () => Int = ... // some calculation val calc2 : () => Int = ... // other calculation value = calc1 value = calc2 val result : Int = value + 1 This piece of code should only call calc2(), not calc1 I have an idea how I can write this container with implicit conversions and and special container class. I'm curios if is there any embedded scala feature that doesn't require me write unnecessary code

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• Excel Worksheet assignment in VB.Net doesn't compile

  - by Brian Hooper

  I'm converting a VB6 application into VB.Net and having trouble with the basics. I start off with:- Dim xl As Excel.Application Dim xlsheet As Excel.Worksheet Dim xlwbook As Excel.Workbook xl = New Excel.Application xlwbook = xl.Workbooks.Open(my_data.file_name) xlsheet = xlwbook.Sheets(1) but the last line doesn't compile; it reports Option Strict On disallows implicit conversion from 'Object' to 'Microsoft.Office.Interop.Excel.Worksheet' I can make this go away by replacing the line with xlsheet = CType(xlwbook.Sheets(1), Excel.Worksheet) but that does't look like the right thing to do to me. If the assignment is correct, I would have thought the object should naturally have the correct type. So: does anyone know what the correct thing I should be doing here?

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• Allocating memory in char * struct

  - by mrblippy

  hi, im trying to read in a word from a user, then dynamically allocate memory for the word and store it in a struct array that contains a char *. i keep getting a implicit declaration of function âstrlenâ so i know im going wrong somewhere. struct class { char class_code[7]; char *name; }; char buffer[101]; struct unit units[1000]; scanf("%s", buffer); units[0].name = (char *) malloc(strlen(buffer)+1); strcpy(units[0].name, buffer);

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• filter functions problem

  - by Adam

  I'm working on a search component for an app I'm working on and I needed to add some filters to it. I've found an example and got the first filter working fine. Now I'm trying to add a second filter I'm running into problems... In the example I found they use filterFunctions, but I only get an option for filterFunction, why is that? Here's the example code productsCollection.filterFunctions = [ filterByPrice, filterByType, filterByCondition, filterByVendor ] And this is what I'm trying acData.filterFunction = [filterByStatus, filterByDate] but with this code I get the following error message - 1067: Implicit coercion of a value of type Array to an unrelated type Function. Why am I getting this error and how would I go about add multiple filters to my Array Collection? Thanks!

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• Problems with variadic macros in C

  - by imikedaman

  Hi, I'm having a problem with optional arguments in #define statements in C, or more specifically with gcc 4.2: bool func1(bool tmp) { return false; } void func2(bool tmp, bool tmp2) {} #define CALL(func, tmp, ...) func(tmp, ##__VA_ARGS__) int main() { // this compiles CALL(func2, CALL(func1, false), false); // this fails with: Implicit declaration of function 'CALL' CALL(func2, false, CALL(func1, false)); } That's obviously a contrived example, but does show the problem. Does anyone know how I can get the optional arguments to "resolve" correctly? Additional information: If I remove the ## before _VA_ARGS_, and do something like this: bool func2(bool tmp, bool tmp2) { return false; } #define CALL(func, tmp, ...) func(tmp, __VA_ARGS__) int main() { CALL(func2, false, CALL(func2, false, false)); } That compiles, but it no longer works with zero arguments since it would resolve to func(tmp, )

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• C# Nullable Type question

  - by TatMing

  for example: int? taxid; if (ddlProductTax.SelectedValue == "") { taxid = null; } else { taxid = Convert.ToInt32(ddlProductTax.SelectedValue); } //Correct But int? taxid; taxid = (ddlProductTax.SelectedValue == "" ? null : Convert.ToInt32(ddlProductTax.SelectedValue)); //Error It error say and int32 cannot implicit convert. The ( ? truepart : falsepart); is not short of (if ..else..) ?

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• Transparent Dialog Alignment

  - by feragusper

  I'm trying to get a custom dialog with a transparent background doing this way: this.getWindow().setBackgroundDrawableResource(R.drawable.transparent); (where "R.drawable.transparent" is a reference to the color "#00000000") The weird issue on this is that I can't align my dialog window. It's always aligned to the left, even if I implicit set the Gravity of the window using: this.getWindow().setGravity(Gravity.CENTER); And if I just comment the line which set the transparent background, the alignment works fine. Any help would be much appreciated! Thanks.

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• Problem using Conditional Operation with Nullable Int

  - by Rajarshi

  A small problem. Any idea guys why this does not work? int? nullableIntVal = (this.Policy == null) ? null : 1; I am trying to return 'null' if the left hand expression is True, else 1. Seems simple but gives compilation error - Type of conditional expression cannot be determined because there is no implicit conversion between 'null' and 'int' If I replace the " ? null : 1 " with any valid int, then there is no problem.

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• Is there any way to retrieve a float from a varargs function's parameters?

  - by Jared P

  If the function was defined with a prototype which explicitly stated the types of the parameters, eg. void somefunc(int arg1, float arg2); but is implemented as void somefunc(int arg1, ...) { ... } is it possible to use va_arg to retrieve a float? It's normally prevented from doing this because varargs functions have implicit type promotions, like float to double, so trying to retrieve an unpromoted type is unsupported, even though the function is being called with the unpromoted type do to the more specific function prototype. The reason for this is to retrieve arguments of different types at runtime, as part of an obj-c interpreter, where one function will be reused for all different types of methods. This would be best as architecture independent (so that if nothing else the same code works on simulator and on device), although if there is no way to do this then device specific fixes will be accepted.

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• Facebook access token: server-side vs client-side flows

  - by alexey

  Facebook docs: Facebook Platform supports two different OAuth 2.0 flows for user login: server-side (known as the authentication code flow in the specification) and client-side (known as the implicit flow). The server-side flow is used whenever you need to call the Graph API from your web server. The client-side flow is used when you need to make calls to the Graph API from a client, such as JavaScript running in a Web browser or from a native mobile or desktop app. What is the difference between access tokens taken by these flows? It seems like they length differ. Can we use server-side flow token on a client? And otherwise, can we use client-side flow token on a server?

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• Allocating memory for a char pointer that is part of a struct

  - by mrblippy

  hi, im trying to read in a word from a user, then dynamically allocate memory for the word and store it in a struct array that contains a char *. i keep getting a implicit declaration of function âstrlenâ so i know im going wrong somewhere. struct class { char class_code[4]; char *name; }; char buffer[101]; struct unit units[1000]; scanf("%s", buffer); units[0].name = (char *) malloc(strlen(buffer)+1); strcpy(units[0].name, buffer);

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• Precision problems of real numbers in Fortran

  - by saladoil

  I've been trying to use Fortran for my research project, with the GNU Fortran compiler (gfortran), latest version, but I've been encountering some problems in the way it processes real numbers. If you have for example the code: program test implicit none real :: y = 23.234, z z = y * 100000 write(*,*) y, z end program You'll get as output: 23.23999 2323400.0. I find this really strange. Can someone tell me what's exactly happening here? Looking at z I can see that y does retain its precision, so for calculations that shouldn't be a problem I suppose. But why is the output of y not exactly the same as the value that I've specified, and what can I do to make it exactly the same?

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• Problem with optional arguments in C #defines

  - by imikedaman

  Hi, I'm having a problem with optional arguments in #define statements in C, or more specifically with gcc 4.2: bool func1(bool tmp) { return false; } void func2(bool tmp, bool tmp2) {} #define CALL(func, tmp, ...) func(tmp, ##__VA_ARGS__) int main() { // this compiles CALL(func2, CALL(func1, false), false); // this fails with: Implicit declaration of function 'CALL' CALL(func2, false, CALL(func1, false)); } That's obviously a contrived example, but does show the problem. Does anyone know how I can get the optional arguments to "resolve" correctly? Additional information: If I remove the ## before _VA_ARGS_, and do something like this: bool func2(bool tmp, bool tmp2) { return false; } #define CALL(func, tmp, ...) func(tmp, __VA_ARGS__) int main() { CALL(func2, false, CALL(func2, false, false)); } That compiles, but it no longer works with zero arguments since it would resolve to func(tmp, )

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• Passing arguments to UILabel [ 2 ] *

  - by DesperateLearner

  I'm trying to call a method of the below (Scroll animation class) type from a viewcontroller class. -(void)CreateLabel:(CGRect )frame andLabel:(UILabel *[NUM_LABELS])label andview:(UIView *)view; I got some errors when I tried passing the argument. Any suggestion on how to call this? This is how I called that method ScrollAnimation *newAnimation = [[ScrollAnimation alloc] init]; [newAnimation CreateLabel:CGRectMake(0, 50, 300,30) andLabel:animateLabel[NUM_LABELS] andview:self.view]; I have the error /Volumes/Red Drive/CarTransition/CarTransition/ViewController.m:120:66: Implicit conversion of an Objective-C pointer to 'UILabel **' is disallowed with ARC /Volumes/Red Drive/CarTransition/CarTransition/ViewController.m:120:66: Incompatible pointer types sending 'UILabel *__strong' to parameter of type 'UILabel **'

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• Size of a class with 'this' pointer

  - by psvaibhav

  The size of a class with no data members is returned as 1 byte, even though there is an implicit 'this' pointer declared. Shouldn't the size returned be 4 bytes(on a 32 bit machine)? I came across articles which indicated that 'this' pointer is not counted for calculating the size of the object. But I am unable to understand the reason for this. Also, if any member function is declared virtual, the size of the class is now returned as 4 bytes. This means that the vptr is counted for calculating the size of the object. Why is the vptr considered and 'this' pointer ignored for calculating the size of object?

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• C# overloading with generics: bug or feature?

  - by TN

  Let's have a following simplified example: void Foo<T>(IEnumerable<T> collection, params T[] items) { // ... } void Foo<C, T>(C collection, T item) where C : ICollection<T> { // ... } void Main() { Foo((IEnumerable<int>)new[] { 1 }, 2); } Compiler says: The type 'System.Collections.Generic.IEnumerable' cannot be used as type parameter 'C' in the generic type or method 'UserQuery.Foo(C, T)'. There is no implicit reference conversion from 'System.Collections.Generic.IEnumerable' to 'System.Collections.Generic.ICollection'. If I change Main to: void Main() { Foo<int>((IEnumerable<int>)new[] { 1 }, 2); } It will work ok. Why compiler does not choose the right overload?

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