C++ “new int(100)”有什么作用？
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What does "new int(100)" do?
提问by JASON
Possible Duplicate:
is this a variable or function
可能重复：
这是变量还是函数
I mistakenly used something like:
我错误地使用了类似的东西：
int *arr = new int(100);
and it passes compile, but I knew this is wrong. It should be
它通过了编译，但我知道这是错误的。它应该是
int *arr = new int[100];
What does the compiler think it is when I wrote the wrong one?
当我写错了编译器会怎么想？
回答by NPE
The first line allocates a single intand initializes it to 100.Think of the int(100)as a constructor call.
第一行分配一个单个int并将其初始化为100. 将int(100)视为构造函数调用。
Since this is a scalar allocation, trying to access arr[1]or to free the memory using delete[]would lead to undefined behaviour.
由于这是标量分配，因此尝试访问arr[1]或释放内存delete[]会导致未定义的行为。
回答by Peopleware
Wikipedia new(C++)quote:
维基百科新（C++）引用：
int *p_scalar = new int(5); //allocates an integer, set to 5. (same syntax as constructors)
int *p_array = new int[5]; //allocates an array of 5 adjacent integers. (undefined values)
UPDATE
更新
In the current Wikipedia article newand delete(C++)the example is removed.
在当前的 Wikipedia 文章new和delete(C++) 中，该示例已被删除。
Additionally here's the less intuitive but fully reliable C++ reference for newand new[].
回答by avakar
It allocates one object of type intand initialized it to value 100.
它分配一个类型的对象int并将其初始化为 value 100。
A lot of people doesn't know that you can pass an initializer to new, there's a particular idiom that should be made more widely known so as to avoid using memset:
很多人不知道你可以将初始化器传递给new，有一个特定的习惯用法应该更广为人知以避免使用memset：
new int[100]();
This will allocate an array of intand zero-initialize its elements.
这将分配一个数组int并对其元素进行零初始化。
Also, you shouldn't be using an array version of new. Ever. There's std::vectorfor that purpose.
此外，您不应该使用new. 曾经。有std::vector这个目的。
回答by Philipp
The first one creates a single new integer, initializes it to the value 100 and returns a pointer to it.
第一个创建一个新整数，将其初始化为值 100 并返回指向它的指针。
In C/C++ there is no difference between a pointer to an array and a pointer to a single value (a pointer to an array is in fact just a pointer to its first element). So this is a valid way to create an array with one element.
在 C/C++ 中，指向数组的指针和指向单个值的指针之间没有区别（指向数组的指针实际上只是指向其第一个元素的指针）。因此，这是创建具有一个元素的数组的有效方法。
