new-operator | 易学教程

Rails 3 Render => New with Parameter

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问题 I'v read: Rails: Pass parameters with render :action? ,but I'm still having problems. My URL for the new page is: http://localhost:3000/submit?category_id=2. Submitting the form the first time works without any problems, but if the creation fails and the controller renders a new page I get an error can't find category without id because the parameter is not being passed. Here's a short version of the new.html.erb and new/create controllers def new ... @category = params[:category_id] @title =

Operator new for Arduino

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问题 I've been told (specifically in an answer to C++ Standard Library on Arduino, and in Stack Overflow question C++ string and Arduino String. How to combine them? )) that the Arduino compiler does not implement the new operator. However, I've written a program for the Arduino (in the Arduino IDE) which uses it, and it works perfectly. void setup() { Serial.begin(9600); } void loop() { char* array; char c; unsigned arraySize; Serial.write("Enter a 1 digit number.\n"); do { c = Serial.read(); }

How array works internally in Java?

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问题 This query is posted to basically understand points like An object is class instance or an array; An array is a subclass of Object class; Everything that is instantiated other than primitive is an object in Java. Here is my understanding of working with arrays in Java. Considering the below program, /* dummy.java */ class C { private int i; public C() { i = 1; System.out.println("Am in constructor"); } } public class dummy { public static void main(String[] args) { C[] c = new C[2]; // Line

Using malloc instead of new, and calling the copy constructor when the object is created

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I wanted to try out TBB's scalable_allocator, but was confused when I had to replace some of my code. This is how allocation is done with the allocator: SomeClass* s = scalable_allocator<SomeClass>().allocate( sizeof(SomeClass) ); EDIT: What's shown above is not how allocation is done with scalable_allocator. As ymett correctly mentioned , allocation is done like this: int numberOfObjectsToAllocateFor = 1; SomeClass* s = scalable_allocator<SomeClass>().allocate( numberOfObjectsToAllocateFor ); scalable_allocator<SomeClass>().construct( s, SomeClass()); scalable_allocator<SomeClass>().destroy(s

int num = new int(); What happens when this line executes?

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问题 Got to know a new thing today that we can create integers by using new operator as below int num = new int(); Now I wonder if I create an integer in this manner then the resulting integer will be a value type or reference type? I guess it will be a value type. I tried the below code int num1 = 10; int num2 = new int(); int num3; num1 = num2; num2 = num3; I got the below build error: Use of unassigned local variable 'num3' I know why this build error is given. But I wonder when and how to use

What does ::new mean?

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When examining the MS directX 11 DXUT example, the following code appeared: template<typename TYPE> HRESULT CGrowableArray <TYPE>::SetSize( int nNewMaxSize ) { int nOldSize = m_nSize; if( nOldSize > nNewMaxSize ) { assert( m_pData ); if( m_pData ) { // Removing elements. Call dtor. for( int i = nNewMaxSize; i < nOldSize; ++i ) m_pData[i].~TYPE(); } } // Adjust buffer. Note that there's no need to check for error // since if it happens, nOldSize == nNewMaxSize will be true.) HRESULT hr = SetSizeInternal( nNewMaxSize ); if( nOldSize < nNewMaxSize ) { assert( m_pData ); if( m_pData ) { // Adding

Operator new[] does not receive extra bytes

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I have such code #include <cstdlib> class Foo { int m_data; public : Foo() : m_data(0) { } /*~Foo() { }*/ static void* operator new[](const size_t size) { return malloc(size); } static void operator delete[](void* data) { free(data); } }; int main() { Foo* objects = new Foo[5]; delete [] objects; } In this case I receive value of size in operator new overloading as 20 bytes as I wanted ( sizeof(int) * 5 ). But if I uncomment the destructor I get size as 24 bytes. Yeah, I now that these extra bytes is used to store the size of allocated memory and equals to sizeof(size_t) . I can't understand

Hiding symbols in a shared library on Mac OS X

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We've been building a large open source software on a variety of platforms (Linux, Windows, Mac OS X, 32-bit and 64-bit) for several years without troubles. Lately however, the Mac OS X build (64-bit) stopped working correctly and started to crash randomly. It more or less coincided with an update of Mac OS X on our build machine from 10.7 to 10.8.2 (but the compiler toolchain didn't change, it's still llvm-gcc 4.2.1). Our application is made of a couple of dynamic (shared) libraries and many executables using them. One of the shared library overrides the new and delete operators for a variety

What does ::new mean?

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问题 When examining the MS directX 11 DXUT example, the following code appeared: template<typename TYPE> HRESULT CGrowableArray <TYPE>::SetSize( int nNewMaxSize ) { int nOldSize = m_nSize; if( nOldSize > nNewMaxSize ) { assert( m_pData ); if( m_pData ) { // Removing elements. Call dtor. for( int i = nNewMaxSize; i < nOldSize; ++i ) m_pData[i].~TYPE(); } } // Adjust buffer. Note that there's no need to check for error // since if it happens, nOldSize == nNewMaxSize will be true.) HRESULT hr =

How to create a new source code branch using TFS API?

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I am trying to create a new branch using the API, and have used both PendBranch() and CreateBranch() . The problem with CreateBranch() is it commits immediately and I want to be able to add comments as the branch is checked in. So, I what I did is shown below. Basically I get all the information like server item and local item to be mapped as well as source and target of the branch from my windows application. Somehow, when I see Source Control Explorer it still says "Not mapped" even though I have given a : workspace.Get() after creating the workspace and workspace.Map(serverItem,localItem)