我在一个c++程序中分配值，就像这样:
#include <iostream>
using namespace std;
int main()
{
int array[2];
array[0] = 1;
array[1] = 2;
array[3] = 3;
array[4] = 4;
cout << array[3] << endl;
cout << array[4] << endl;
return 0;
}
程序输出3和4。这应该是不可能的。我使用g++ 4.3.3
下面是编译和运行命令
$ g++ -W -Wall errorRange.cpp -o errorRange
$ ./errorRange
3
4
只有当分配数组[3000]=3000时，它才会给我一个分割错误。
如果gcc不检查数组边界，我怎么能确定我的程序是正确的，因为它可能导致一些严重的问题以后?
我将上面的代码替换为
vector<int> vint(2);
vint[0] = 0;
vint[1] = 1;
vint[2] = 2;
vint[5] = 5;
cout << vint[2] << endl;
cout << vint[5] << endl;
这个也不会产生误差。
The behavior can depend on your system. Typically, you will have a margin for out of bounds, sometimes with value of 0 or garbage values. For the details you can check with memory allocation mechanism used in your OS. On top of that, if you use the programming language like c/c++, it will not check the bounds when you using some containers, like array. So, you will meet "undefined event" because you do not know what the OS did below the surface. But like the programming language Java, it will check the bound. If you step outside of the bound, you will get an exception.
Hint
如果你想要快速约束大小数组的范围错误检查，尝试使用boost::array，(也std::tr1::array from <tr1/array>，它将是下一个c++规范的标准容器)。它比std::vector快得多。它在堆上或类实例内部保留内存，就像int array[]一样。
这是一个简单的示例代码:
#include <iostream>
#include <boost/array.hpp>
int main()
{
boost::array<int,2> array;
array.at(0) = 1; // checking index is inside range
array[1] = 2; // no error check, as fast as int array[2];
try
{
// index is inside range
std::cout << "array.at(0) = " << array.at(0) << std::endl;
// index is outside range, throwing exception
std::cout << "array.at(2) = " << array.at(2) << std::endl;
// never comes here
std::cout << "array.at(1) = " << array.at(1) << std::endl;
}
catch(const std::out_of_range& r)
{
std::cout << "Something goes wrong: " << r.what() << std::endl;
}
return 0;
}
这个程序将打印:
array.at(0) = 1
Something goes wrong: array<>: index out of range
