blocks|key|1773743|text|解释堆栈和堆之间的区别以及对象的位置。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1773744|诸如结构(+C%2B%2B和C#)之类的值类型被放入堆栈。引用类型(类实例)被放到堆上。指针(或引用)指向该特定实例在堆上的内存位置。|1773745|引用类型是关键字。在C%2B%2B中使用指针就像在C#中使用ref关键字一样。|offset|length|style|CODE|1773746|托管应用程序使得使用这些东西变得容易，因此.NET开发人员可以省去麻烦和困惑。幸好我不再做C语言了。|1773747|entityMap^0|0|0|Q|3|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|P|8|@$F|Q|G|R|H|I]]|9|@]|A|$]]|$1|J|3|K|5|6|7|S|8|@]|9|@]|A|$]]|$1|L|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|M|$]]

Explain the difference between the stack and the heap and where objects go. 

Value types such as structs (both C++ and C#) go on the stack. Reference types (class instances) get put on the heap. A pointer (or reference) points to the memory location on the heap for that specific instance.

Reference type is the key word. Using a pointer in C++ is like using <code>ref</code> keyword in C#.

Managed apps make working with this stuff easy so .NET devs are spared the hassle and confusion. Glad I don't do C anymore.

blocks|key|1773769|text|在C#中，对类的所有引用大致等同于C%2B%2B世界中的指针。对于值类型(结构、整数等)事实并非如此。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1773770|C#：|1773771|void+func1(string+parameter)
void+func2(int+parameter)|code-block|syntax|javascript|1773772|C%2B%2B：|1773773|void+func1(string*+parameter)
void+func2(int+parameter)|1773774|在C#中使用ref关键字传递参数等效于在C%2B%2B中通过引用传递参数。|offset|length|style|CODE|1773775|1773776|void+func1(ref+string+parameter)
void+func2(ref+int+parameter)|1773777|C%2B%2B：|1773778|void+func1((string*)&+parameter)
void+func2(int&+parameter)|1773779|如果参数是一个类，就像通过引用传递指针一样。|1773780|entityMap^0|0|0|0|0|0|6|3|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|13|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|14|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|15|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|16|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|17|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|18|8|@$O|19|P|1A|Q|R]]|9|@]|A|$]]|$1|S|3|C|5|6|7|1B|8|@]|9|@]|A|$]]|$1|T|3|U|5|F|7|1C|8|@]|9|@]|A|$G|H]]|$1|V|3|W|5|6|7|1D|8|@]|9|@]|A|$]]|$1|X|3|Y|5|F|7|1E|8|@]|9|@]|A|$G|H]]|$1|Z|3|10|5|6|7|1F|8|@]|9|@]|A|$]]|$1|11|3|-4|5|6|7|1G|8|@]|9|@]|A|$]]]|12|$]]

In C#, all references to classes are roughly the equivalent to pointers in the C++ world. For value types (structs, ints, etc..) this is not the case. 

C#: 

<pre><code>void func1(string parameter)
void func2(int parameter)
</code></pre>

C++: 

<pre><code>void func1(string* parameter)
void func2(int parameter)
</code></pre>

Passing a parameter using the <code>ref</code> keyword in C# is equivalent to passing a parameter by reference in C++. 

C#: 

<pre><code>void func1(ref string parameter)
void func2(ref int parameter)
</code></pre>

C++: 

<pre><code>void func1((string*)&amp; parameter)
void func2(int&amp; parameter)
</code></pre>

If the parameter is a class, it would be like passing a pointer by reference.

blocks|key|1987611|text|对我来说，关键是理解记忆的工作方式。变量存储在内存中。可以在内存中放置变量的位置是有编号的。指针是保存此数字的变量。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1987612|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

The key for me was to understand the way memory works. Variables are stored in memory. The places in which you can put variables in memory are numbered. A pointer is a variable that holds this number.

blocks|key|1773871|text|C#中的引用与C%2B%2B中的指针的作用相同，没有所有杂乱的语法。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1773872|考虑以下C#代码：|1773873|public+class+A
{
++++public+int+x;
}

public+void+AnotherFunc(A+a)
{
++++a.x+=+2;
}

public+void+SomeFunc()
{
++++A+a+=+new+A();
++++a.x+=+1;

++++AnotherFunc(a);
++++//+a.x+is+now+2
}|code-block|syntax|javascript|1773874|因为类是引用类型，所以我们知道我们正在向AnotherFunc传递一个现有的A实例(与复制的值类型不同)。|offset|length|style|CODE|1773875|在C%2B%2B中，我们使用指针来明确这一点：|1773876|class+A
{
public:
++++int+x;
};

void+AnotherFunc(A*+a)+//+notice+we+are+pointing+to+an+existing+instance+of+A
{
++++a->x+=+2;
}

void+SomeFunc()
{
++++A+a;
++++a.x+=+1;

++++AnotherFunc(&a);
++++//+a.x+is+now+2
}|1773877|entityMap^0|0|0|0|K|B|12|1|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|V|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|W|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|X|8|@$K|Y|L|Z|M|N]|$K|10|L|11|M|N]]|9|@]|A|$]]|$1|O|3|P|5|6|7|12|8|@]|9|@]|A|$]]|$1|Q|3|R|5|F|7|13|8|@]|9|@]|A|$G|H]]|$1|S|3|-4|5|6|7|14|8|@]|9|@]|A|$]]]|T|$]]

References in C# act the same way as pointers in C++, without all the messy syntax.

Consider the following C# code:

<pre><code>public class A
{
 public int x;
}

public void AnotherFunc(A a)
{
 a.x = 2;
}

public void SomeFunc()
{
 A a = new A();
 a.x = 1;

 AnotherFunc(a);
 // a.x is now 2
}
</code></pre>

Since classes are references types, we know that we are passing an existing instance of <code>A</code> to <code>AnotherFunc</code> (unlike value types, which are copied).

In C++, we use pointers to make this explicit:

<pre><code>class A
{
public:
 int x;
};

void AnotherFunc(A* a) // notice we are pointing to an existing instance of A
{
 a-&gt;x = 2;
}

void SomeFunc()
{
 A a;
 a.x = 1;

 AnotherFunc(&amp;a);
 // a.x is now 2
}
</code></pre>

blocks|key|1774218|text|任何理解类和结构之间语义差异的C#程序员都应该能够理解指针。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1774219|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Any C# programmer that understands the semantic differences between classes and structs should be able to understand pointers. I.e., explaining in terms of value vs. reference semantics (in .NET terms) should get the point across; I wouldn't complicate things by trying to explain in terms of <code>ref</code> (or <code>out</code>).

blocks|key|1988042|text|“如何仅使用.NET或Java开发人员熟悉的概念来解释指针？”我建议确实有两件不同的事情需要学习。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1988043|第一个是如何使用指针和堆分配内存来解决特定问题。有了适当的风格，例如使用shared_ptr<>，这可以以类似于Java的方式来完成。shared_ptr<>与Java对象句柄有许多共同之处。|1988044|然而，其次，我认为指针通常是一个根本较低级别的概念，Java和较小程度的C#故意隐藏。在C%2B%2B中编程而不移动到那个级别肯定会有一大堆问题。您需要从底层内存布局的角度考虑，并将指针视为指向特定存储部分的指针。|1988045|试图从更高的概念来理解这个较低的层次将是一条奇怪的道路。|1988046|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|L|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|M|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|I|$]]

"How can pointers be explained using only concepts that are familiar to a .NET or Java developer? "
I'd suggest that there are really two distinct things that need to be learnt.

The first is how to use pointers, and heap allocated memory, to solve specific problems. With an appropriate style, using shared_ptr&lt;> for example, this can be done in a manner analogous to that of Java. A shared_ptr&lt;> has a lot in common with a Java object handle.

Secondly, however, I would suggest that pointers in general are a fundamentally lower level concept that Java, and to a lesser extent C#, deliberately hides. To program in C++ without moving to that level will guarantee a host of problems. You need to think in terms of the underlying memory layout and think of pointers as literally pointers to specific pieces of storage. 

To attempt to understand this lower level in terms of higher concepts would be an odd path to take.

blocks|key|1988115|text|准备两张大幅面的图表纸，一些剪刀和一位朋友来帮助你。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1988116|纸张上的每个方块代表一个字节。|1988117|一张纸就是堆栈。|1988118|另一个表是堆。把堆交给你的朋友--他是内存管理器。|1988119|您将伪装成一个C程序，并且需要一些内存。当运行你的程序时，从堆栈和堆中剪切出代表内存分配的块。|1988120|准备好的?|1988121|void+main()+{
++++int++a;+++++++++++++++++++++++/*+Take+four+bytes+from+the+stack.+*/
++++int+*b+=+malloc(sizeof(int));+/*+Take+four+bytes+from+the+heap.+*/

++++a+=+1;++/*+Write+on+your+first+little+bit+of+graph+paper,+WRITE+IT!+*/
++++*b+=+2;+/*+Get+writing+(on+the+other+bit+of+paper)+*/

++++b+=+malloc(sizeof(int));+/*+Take+another+four+bytes+from+the+heap.+
++++++++++++++++++++++++++++++++Throw+the+first+'b'+away.+Do+NOT+give+it+
++++++++++++++++++++++++++++++++back+to+your+friend+*/

++++free(b);+/*+Give+the+four+bytes+back+to+your+friend+*/
++++*b+=+3;++/*+Your+friend+must+now+kill+you+and+bury+the+body+*/
}+/*+Give+back+the+four+bytes+that+were+'a'+*/|code-block|syntax|javascript|1988122|尝试使用一些更复杂的程序。|1988123|entityMap^0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|V|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|W|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|X|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|Y|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|Z|8|@]|9|@]|A|$]]|$1|L|3|M|5|N|7|10|8|@]|9|@]|A|$O|P]]|$1|Q|3|R|5|6|7|11|8|@]|9|@]|A|$]]|$1|S|3|-4|5|6|7|12|8|@]|9|@]|A|$]]]|T|$]]

Get two sheets of large format graph paper, some scissors and a friend to help you.

Each square on the sheets of paper represents one byte.

One sheet is the stack.

The other sheet is the heap. Give the heap to your friend - he is the memory manager.

You are going to pretend to be a C program and you'll need some memory. When running your program, cut out chunks from the stack and the heap to represent memory allocation.

Ready?

<pre><code>void main() {
 int a; /* Take four bytes from the stack. */
 int *b = malloc(sizeof(int)); /* Take four bytes from the heap. */

 a = 1; /* Write on your first little bit of graph paper, WRITE IT! */
 *b = 2; /* Get writing (on the other bit of paper) */

 b = malloc(sizeof(int)); /* Take another four bytes from the heap. 
 Throw the first 'b' away. Do NOT give it 
 back to your friend */

 free(b); /* Give the four bytes back to your friend */
 *b = 3; /* Your friend must now kill you and bury the body */
} /* Give back the four bytes that were 'a' */
</code></pre>

Try with some more complex programs.

I am a C#/Java developer trying to learn C++. As I try to learn the concept of pointers, I am struck with the thought that I must have dealt with this concept before. How can pointers be explained using only concepts that are familiar to a .NET or Java developer? Have I really never dealt with this, is it just hidden to me, or do I use it all the time without calling it that?

How do you explain C++ pointers to a C#/Java developer?

内存管理

Java

我是一名C#/Java开发人员，正在努力学习C++。当我试图学习指针的概念时，我突然想到我以前一定处理过这个概念。如何仅使用.NET或Java开发人员熟悉的概念来解释指针？我真的从来没有处理过这个问题吗，它对我来说只是隐藏的，还是我一直在使用它，而没有调用它？

问如何解释指向C#/ C++开发人员的Java指针？
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