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首先看看我的代码。它在在线法官上给出运行时错误（sigsegv），但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< 数量 <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 运行了这个简单的代码。它给出了以下输出，我是 valgrind 的新手，所以请告诉我这是什么意思。

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)
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1 回答 1

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Valgrind 在这里基本上告诉你两件事：

1° 您正在写入未分配的内存位置。这就是invalid write消息的意义。此写入大小为 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，对于 j 的某些值，您的 a[j] 超出了数组的范围，因此您要正确检查（更具体地说，请记住数组是 0 索引的，因此数组的范围 a大小为 s 的为 a[0] 到 a[s-1])。
你应该打印j并检查它是否小于10,000，看看是否有问题。

2° 退出时，您完成了 1 次分配，但 0 次空闲，因此您没有释放分配的 400,000 字节。但是，在退出时您仍然有一个指针，所以它是still reachable.

于 2012-08-24T10:26:38.613 回答