blocks|key|316091|text|triangles+=+new+int[numTriangles*3];|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|316092|然后以如下方式访问它：|unstyled|316093|triangles[numTriangles*triangleIndex%2BvertexIndex]+=+blah;|316094|但这很乏味且容易出错，所以我建议使用boost.multi_array，或者使用您自己的代码(非常简单)：|offset|length|316095|template<class+T>
class+Matrix+{
public:
++++Matrix(int+_w,+int+_h)+:+data(_w*_h),+w(_w),+h(_h)+{
++++}

++++T++++++&+operator()(int+x,+int+y)+++++++{+return+data[y+*+w+%2B+x];+}
++++T+const&+operator()(int+x,+int+y)+const+{+return+data[y+*+w+%2B+x];+}

private:
++++std::vector<T>+data;
++++int+w,+h;
};

//+usage:
int+main()+{
++++Matrix<float>+triangles(numTriangles,+3);
++++triangles(triangleIndex,+vertexIndex)+=+blah;
}|316096|另一方面，如果您实际上想要一个三角形数组，而不是二维数组，那么只需使用vector<Triangle>，其中Triangle是一个类:)|style|CODE|316097|entityMap|0|LINK|mutability|MUTABLE|url|http://www.boost.org/doc/libs/1_38_0/libs/multi_array/doc/index.html^0|0|0|0|I|H|0|0|0|Z|G|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|11|8|@]|9|@]|A|$]]|$1|G|3|H|5|6|7|12|8|@]|9|@]|A|$B|C]]|$1|I|3|J|5|F|7|13|8|@]|9|@$K|14|L|15|1|16]]|A|$]]|$1|M|3|N|5|6|7|17|8|@]|9|@]|A|$B|C]]|$1|O|3|P|5|F|7|18|8|@$K|19|L|1A|Q|R]]|9|@]|A|$]]|$1|S|3|-4|5|F|7|1B|8|@]|9|@]|A|$]]]|T|$U|$5|V|W|X|A|$Y|Z]]]]

<pre><code>triangles = new int[numTriangles*3];
</code></pre>

Then access it as:

<pre><code>triangles[numTriangles*triangleIndex+vertexIndex] = blah;
</code></pre>

But this is tedious and error prone so I suggest using <a href="http://www.boost.org/doc/libs/1_38_0/libs/multi_array/doc/index.html" rel="nofollow noreferrer">boost.multi_array</a> instead, or rolling your own (really simple):

<pre><code>template&lt;class T&gt;
class Matrix {
public:
 Matrix(int _w, int _h) : data(_w*_h), w(_w), h(_h) {
 }

 T &amp; operator()(int x, int y) { return data[y * w + x]; }
 T const&amp; operator()(int x, int y) const { return data[y * w + x]; }

private:
 std::vector&lt;T&gt; data;
 int w, h;
};

// usage:
int main() {
 Matrix&lt;float&gt; triangles(numTriangles, 3);
 triangles(triangleIndex, vertexIndex) = blah;
}
</code></pre>

If, on the other hand, you actually want an array of triangles, rather than a twodimensional array, just use a <code>vector&lt;Triangle&gt;</code> where Triangle is a class :)

blocks|key|316126|text|c%2B%2B中的多维数组只是语法上的糖。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|316127|int+a[n][m];|code-block|syntax|javascript|316128|等同于|316129|int+a[n*m];|316130|所以你只需要一个普通的指针--比如：|316131|int+*triangles;
triangles+=+new+int[numTriangles*3];|316132|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|U|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

Multidimensional arrays in c++ are just syntactic sugar.

<pre><code>int a[n][m];
</code></pre>

is equivalent to

<pre><code>int a[n*m];
</code></pre>

so you just need a regular pointer - i.e.:

<pre><code>int *triangles;
triangles = new int[numTriangles*3];
</code></pre>

blocks|key|4381380|text|错误消息说:)如果你新建一个数组，那么new返回一个指向它的第一个元素的指针。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4381381|多维数组只是数组数组的另一个名称。你得到了一个包含int[3]的数组，以及这些元素中的numTriangles元素。所以new要做的就是返回一个指向int[3]的指针。你赋予结果的变量必须具有该类型，这是一个指向3个整数数组的指针：|offset|length|style|CODE|4381382|int+(*triangles)[3];
triangles+=+new+int[numTriangles][3];
triangles[triangleIndex][vertexIndex]+=+42;|code-block|syntax|javascript|4381383|当然，typedefs在这方面也有帮助：|4381384|typedef+int+triangles_t[3];
triangles_t+*+triangles+=+new+int[numTriangles][3];|4381385|由于C%2B%2B优先规则，因此需要使用括号。它们告诉编译器，它创建的不是指向整数的三个指针的数组，而是指向三个整数的数组的指针。这类似于函数指针("void+(*funptr)()")上更常见的用法...|4381386|entityMap^0|0|P|6|22|6|0|0|0|0|1Y|I|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|V|8|@$D|W|E|X|F|G]|$D|Y|E|Z|F|G]]|9|@]|A|$]]|$1|H|3|I|5|J|7|10|8|@]|9|@]|A|$K|L]]|$1|M|3|N|5|6|7|11|8|@]|9|@]|A|$]]|$1|O|3|P|5|J|7|12|8|@]|9|@]|A|$K|L]]|$1|Q|3|R|5|6|7|13|8|@$D|14|E|15|F|G]]|9|@]|A|$]]|$1|S|3|-4|5|6|7|16|8|@]|9|@]|A|$]]]|T|$]]

Well, the error message says it :) If you 'new an array, then new returns a pointer to its first element. 

A multidimensional array is just another name for an array of arrays. You 'newed an array of <code>int[3]</code>, and precisely numTriangles elements of those. So what new does is returning a pointer to <code>int[3]</code>. The variable you assign the result to has to have that type, which is a pointer to an array of 3 integers:

<pre><code>int (*triangles)[3];
triangles = new int[numTriangles][3];
triangles[triangleIndex][vertexIndex] = 42;
</code></pre>

Of course, typedefs also help here:

<pre><code>typedef int triangles_t[3];
triangles_t * triangles = new int[numTriangles][3];
</code></pre>

The parentheses are needed because of the C++ precedence rules. They tell the compiler that it's not creating an array of three pointers to integers, but a pointer to an array of 3 integers. This is similar to the more common use on function pointers (<code>"void (*funptr)()"</code>)...

blocks|key|1025810|text|为此，您必须遍历一个维度并为另一个维度分配空间：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1025811|int**+triangles;
triangles+=+new+int*[NUMROWS];

for+(int+i+=+0;+i+<+NUMROWS;+i%2B%2B)+{
+++triangles[i]+=+new+int[NUMCOLS];
}|code-block|syntax|javascript|1025812|但是在这样做的时候要小心，你将不得不做同样的事情来释放内存。|1025813|for+(int+i+=+0;+i+<+NUMROWS;+i%2B%2B)+{
+++delete+[]+triangles[i];
+++triangles[i]+=+0;
}
delete+[]+triangles;
triangles+=+0;|1025814|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

To do this, you will have to loop over one dimension and allocate space for the other dimension:

<pre><code>int** triangles;
triangles = new int*[NUMROWS];

for (int i = 0; i &lt; NUMROWS; i++) {
 triangles[i] = new int[NUMCOLS];
}
</code></pre>

But be careful when doing it this way, you'll have to do the same to deallocate the memory.

<pre><code>for (int i = 0; i &lt; NUMROWS; i++) {
 delete [] triangles[i];
 triangles[i] = 0;
}
delete [] triangles;
triangles = 0;
</code></pre>

how do I make a pointer to a multidimensional array, which have a unknown size? I've tried this:

<code>int **triangles;</code>

<code>triangles = new int[numTriangles][3];</code>

But i get this error:

<code>cannot convert 'int (*)[3]' to 'int**' in assignment</code>

How do I make a pointer to a multidimensional array which has an unknown size?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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如何使指针指向大小未知的多维数组？我试过了：int **triangles;triangles = new int[numTriangles][3];但是我得到了这个错误：cannot convert 'int (*)[3]' to 'int**' in assignment

问如何使指针指向大小未知的多维数组？
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问如何使指针指向大小未知的多维数组？EN