使用非常变量声明数组大小

I always thought that when declaring an array in C++, the size has to be a constant integer value.

我一直认为在c++中声明数组时，大小必须是一个常量整数值。

For instance :

例如:

int MyArray[5]; // correct

或

const int ARRAY_SIZE = 6;
int MyArray[ARRAY_SIZE]; // correct

but

但

int ArraySize = 5;
int MyArray[ArraySize]; // incorrect

Here is also what is explained in The C++ Programming Language, by Bjarne Stroustrup :

下面是Bjarne Stroustrup在c++编程语言中解释的内容:

The number of elements of the array, the array bound, must be a constant expression (§C.5). If you need variable bounds, use a vector(§3.7.1, §16.3). For example:

数组元素的个数,数组绑定,必须是一个常量表达式(§C.5)。如果你需要变量范围,使用一个向量(§3.7.1,§16.3)。例如:

void f(int i) { 
   int v1[i];          // error : array size not a constant expression
   vector<int> v2(i);  // ok 
}

But to my big surprise, the code above does compile fine on my system !

但令我吃惊的是，上面的代码在我的系统上编译得很好!

Here is what I tried to compile :

以下是我试图汇编的:

void f(int i) {
   int v2[i];
}

int main()
{
   int i = 3;
   int v1[i];
   f(5);
}

I got no error ! I'm using GCC v4.4.0.

我没有出错!我用GCC v4.4.0。

Is there something I'm missing ?

我是不是漏掉了什么?

2 个解决方案

#1

This is a GCC extension to the standard: see here.

这是标准的GCC扩展:请参见这里。

You can use the -pedantic option to cause GCC to issue a warning, or -std=c++98 to make in an error, when you use one of these extensions (in case portability is a concern).

当您使用这些扩展之一时，您可以使用-pedantic选项导致GCC发出警告，或者-std=c++98出错(考虑到可移植性)。

#2

You are using a feature from C99 which is called VLA(variable length arrays). It would be better if you compile your program like this:

您正在使用C99中的一个特性，该特性称为VLA(可变长度数组)。如果你这样编译你的程序会更好:

g++ -Wall -std=c++98 myprog.cpp

#1