在64位系统中分配超过4GB的内存 [英] Allocating more than 4GB memory in a 64 bit system

问题描述

我运行这个代码，编译64位vc ++ 2005，在Windows Server 2008 R2与32GB。在for循环中有一个访问冲突。

  #include< iostream> 
 using namespace std; 
 
 
 int main（int argc，char * argv []）
 {
 double * x = new double [536870912]; 
 
 cout<< memory allocated<< endl 
 
 for（long int i = 0; i <536870912; i ++）
 {
 cout< i<< endl 
 x [i] = 0; 
} 
 
 delete [] x; 
 return 0; 
} 
  

所以如果在新的double [536870912]中没有异常，

另一点值得一提的是，这个程序在另一台计算机上成功测试。

$ b

• long int是32位：这意味着你的最大值是2147483647和sizeof（双）* 536870912> = 2147483647.（我真的不知道这是否有意义，它可能取决于编译器的工作原理）


• 您的分配失败。

我建议您测试以下代码：

 ＃include< conio.h> 
 #include< iostream> 
 using namespace std; 
 
 #define MYTYPE unsigned long long 
 
 
 int main（int argc，char * argv []）
 {
 //测试编译模式
 if（sizeof（void *）== 8）cout<< 编译64位< endl 
 else cout<< 编译32位< endl 
 
 //测试mytype的大小
 cout<< Sizeof：< sizeof（MYTYPE）< endl 
 MYTYPE len; 
 
 //获取<<< doubles>>分配
 cout<< 你想要多少双？ << endl 
 cin>> len; 
 double * x = new（std :: nothrow）double [len]; 
 //测试分配
 if（NULL == x）
 {
 cout< 无法分配< endl 
 return 0; 
} 
 cout<< memory allocated<< endl 
 
 //将所有值设置为0 
 for（MYTYPE i = 0; i  {
 if（i％100000 == 0 ）cout < i<< endl 
 x [i] = 0; 
} 
 
 //在发布之前等待，测试内存使用
 cout<< 按< Enter>键以继续...; 
 getch（）; 
 
 //可用内存。 
 delete [] x; 
 
} 
  

编辑：使用这个代码， 9GB的区块。

I'm running this code, compiled on 64 bits vc++ 2005, on Windows Server 2008 R2 with 32GB. There is an access violation inside the for loop.

#include <iostream>
using namespace std;


int main(int argc, char* argv[])
{   
    double *x = new double[536870912];

    cout << "memory allocated" << endl;

    for(long int i = 0; i < 536870912; i++)
    {   
        cout << i << endl;
        x[i] = 0;
    }

    delete [] x;
    return 0;
}

So if there is no exception in new double[536870912], why am I getting an access violation when doing an assignment over a particular array position?

Another point worth mentioning is that this program was succesfully tested on another computer.

解决方案

It is probably one of the following problem:

• long int is 32-bits: that mean your maximum value is 2147483647, and sizeof(double)*536870912 >= 2147483647. (I don't really know if that has sense. It probably depend on how the compiller work)
• Your allocation is failing.

I suggest you to test the following code:

#include<conio.h>
#include <iostream>
using namespace std;

#define MYTYPE unsigned long long


int main(int argc, char* argv[])
{   
    // Test compiling mode
    if (sizeof(void*) == 8) cout << "Compiling 64-bits" << endl;
    else cout << "Compiling 32-bits" << endl;

    // Test the size of mytype
    cout << "Sizeof:" << sizeof(MYTYPE) << endl;
    MYTYPE len;

    // Get the number of <<doubles>> to allocate
    cout << "How many doubles do you want?" << endl;
    cin >> len;
    double *x = new (std::nothrow) double[len];
    // Test allocation
    if (NULL==x)
    {
        cout << "unable to allocate" << endl;
        return 0;
    }
    cout << "memory allocated" << endl;

    // Set all values to 0
    for(MYTYPE i = 0; i < len; i++)
    {   
        if (i%100000==0) cout << i << endl;
        x[i] = 0;
    }

    // Wait before release, to test memory usage
    cout << "Press <Enter> key to continue...";
    getch();

    // Free memory.
    delete [] x;

}

Editing: Using this code, i just achieved allocate a single block of 9GB.

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