Question

首先看一下我的代码。它给在线裁判提供运行时错误（sigsegv），虽然在我的计算机上工作得很好。请帮我找出错误。

约束是：

0℃; t1 <1000000

0℃; num <100000000

#include<stdio.h>

#include<malloc.h>

int *a;

int main()

{

   a = malloc(sizeof(int)*100000000);



   int  t=3,j,k1,k=1,n=0,i,t1,num;



   for(i=1;i<10000;i++)

      {

                  // m=i*i;

                   n=n+t;

                   for(j=i*i;j<=n;j++)



                                    a[j]=k;



                   k++;

                   t=t+2;



     }

  scanf("%d",&t1);



   for(k1=0;k1<t1;k1++)

   {

        scanf("%d",&num);

        printf("%d\n",a[num]);

   }

  free(a);

  //getch();

   return 0;

}

我使用valgrind运行这个简单的代码。它给出了以下输出，我是valgrind的新手，所以请告诉我它是什么意思。

singu@singu-Studio-1450 ~ $ valgrind --leak-check=yes ./doors
==4732== Memcheck, a memory error detector
==4732== Copyright (C) 2002-2010, and GNU GPL'd, by Julian Seward et al.
==4732== Using Valgrind-3.6.1 and LibVEX; rerun with -h for copyright info
==4732== Command: ./doors
==4732== 
==4732== Warning: set address range perms: large range [0x51c3040, 0x1cf3b440)     (undefined)
==4732== Invalid write of size 4
==4732==    at 0x400662: main (doors.c:16)
==4732==  Address 0x1cf3b440 is 0 bytes after a block of size 400,000,000 alloc'd
==4732==    at 0x4C28FAC: malloc (vg_replace_malloc.c:236)
==4732==    by 0x400605: main (doors.c:6)
==4732== 
^C==4732== 
==4732== HEAP SUMMARY:
==4732==     in use at exit: 400,000,000 bytes in 1 blocks
==4732==   total heap usage: 1 allocs, 0 frees, 400,000,000 bytes allocated
==4732== 
==4732== LEAK SUMMARY:
==4732==    definitely lost: 0 bytes in 0 blocks
==4732==    indirectly lost: 0 bytes in 0 blocks
==4732==      possibly lost: 0 bytes in 0 blocks
==4732==    still reachable: 400,000,000 bytes in 1 blocks
==4732==         suppressed: 0 bytes in 0 blocks
==4732== Reachable blocks (those to which a pointer was found) are not shown.
==4732== To see them, rerun with: --leak-check=full --show-reachable=yes
==4732== 
==4732== For counts of detected and suppressed errors, rerun with: -v
==4732== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 4 from 4)

Answer 1

Valgrind在这里告诉你两件事：

1°您正在写入未分配的内存位置。这是invalid write消息的含义。该写入的大小为4（整数），发生在door.c的第16行这可能是您的分段错误的原因。我的猜测是你的a [j]出现在j的某些值的数组范围之外，所以你想要正确地检查它（更具体地说，记住数组是0索引的，所以数组的范围是尺寸s是[0]到[s-1]）您应该打印j并检查它是否小于10,000以查看是否存在问题。

2°退出时，您已完成1个alloc，但是0可用，因此您不会释放您分配的400,000个字节。但是，退出时仍然有一个指针，因此它是still reachable。

valgrind：以下摘要告诉我们什么

1 个答案: