运行时错误（SIGSEGV）
#include<iostream>
#include<string>
using namespace std;
int main()
{
char arr[1000][80];
char output[1000][80];
int n,i,j;
int num[1000];
cin>>n;
for(i=0;i<n;i++)
{
cin>>num[i];
cin>>arr[i];
}
for(i=0;i<n;i++)
{
for(j=(num[i]-1);j<(strlen(arr[i])-1);j++)
{
arr[i][j]=arr[i][j+1];
}
arr[i][j]='\0';
cout<<"\n"<<(i+1)<<" "<<arr[i];
}
return 0;
}
这是在 Spoj 上上传时出现上述错误的代码。相同的代码在 Borland C++ 上运行良好。
#include<iostream>
#include<string>
using namespace std;
int main()
{
char arr[1000][80];
char output[1000][80];
int n,i,j;
int num[1000];
cin>>n;
for(i=0;i<n;i++)
{
cin>>num[i];
cin>>arr[i];
}
for(i=0;i<n;i++)
{
for(j=(num[i]-1);j<(strlen(arr[i])-1);j++)
{
arr[i][j]=arr[i][j+1];
}
arr[i][j]='\0';
cout<<"\n"<<(i+1)<<" "<<arr[i];
}
return 0;
}
This is the code which while uploading on Spoj gives the above error. The same code runs fine on Borland C++.
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评论（3）
根据传递给该程序的输入，变量
n可能超过 1000，cin>>arr[i]可能读取超过 80 个字符，并且如果num[i] <= 0 || num[i] >= 80那么您将索引超过字符串之一的开头或结尾。所有这些问题的存在都是因为此代码使用固定大小的数组并且不执行任何边界检查。Depending on the input you pass to this program, the variable
nmay be more than 1000,cin>>arr[i]may read more than 80 characters, and ifnum[i] <= 0 || num[i] >= 80then you will index past the beginning or end of one of your strings. All of these problems exist because this code uses fixed-size arrays and doesn't do any bounds checking.乍一看，没有什么本质上的错误。然而，当提供代码无法处理的输入时，段错误肯定是很有可能的。
例如，没有什么可以阻止在输入时写入
arr的边界之外。是否有特定的输入导致此失败？
There's nothing inherently wrong as far as I can see at first glance. However a segfault is certainly very possible when providing inputs your code can't cope with.
There's nothing preventing from writing outside the boundaries of
arron input for example.Is there a specific input for which this fails?
变量
n的值可以大于数组边界。这就是为什么您的代码可能会给出数组索引越界异常，进而给出运行时错误 (SIGSEGV)。The value of the variable
ncan be greater than the array bounds. That is why your code can give an array index out of bounds exception, and consequently why it gives a runtime error (SIGSEGV).