没有出界失误的 [英] No out of bounds error

问题描述

我必须用C本code这需要在一堆字符取值

 ＃包括LT＆;＆stdio.h中GT;
＃定义NEWLINE的'\\ n'
诠释的main（）
{焦炭℃;
炭海峡[6];
INT I = 0;
而（（（C =的getchar（））！= NEWLINE））
{
        海峡[I] = C;
        ++我;
        的printf（％d个\\ N，I）;
}返回0;
}
 

输入是：testtesttest

输出：
1
2
3
4
五
6
7
8
117
118
119
120

我的问题是：

1. 为什么我没有得到一个出界（分段错误）例外，虽然我清楚地超过数组的容量？




2. 为什么输出的数字一下子跳到非常大的数字？

我用C尝试这样做++，得到了相同的行为。任何人都可以请解释究竟是什么原因呢？

解决方案

1. C不检查数组边界。如果您尝试取消引用指针指向的内存，你的程序没有权限访问时才会发生分段错误。只要将过去的数组到底是不太可能导致该行为。未定义行为就是这样 - 不确定的。它可能的显示的工作得很好，但你不应该依靠其安全性。


2. 您的程序通过访问内存过去数组末尾导致不确定的行为。在这种情况下，它看起来像一个你的海峡[i] = C 写会覆盖 i的值。


3. C ++具有相同的规则为C确实在这种情况下。

I have this code in C which takes in bunch of chars

#include<stdio.h> 
# define NEWLINE '\n'
int main()
{

char c;
char str[6];
int i = 0;
while( ((c = getchar()) != NEWLINE))
{
        str[i] = c;
        ++i;
        printf("%d\n", i);
}

return 0;
}

Input is: testtesttest

Output: 1 2 3 4 5 6 7 8 117 118 119 120

My questions are:

1. Why don't I get an out of bounds (segmentation fault) exception although I clearly exceed the capacity of the array?

2. Why do the numbers in the output suddenly jump to very big numbers?

I tried this in C++ and got the same behavior. Could anyone please explain what is the reason for this?

解决方案

1. C doesn't check array boundaries. A segmentation fault will only occur if you try to dereference a pointer to memory that your program doesn't have permission to access. Simply going past the end of an array is unlikely to cause that behaviour. Undefined behaviour is just that - undefined. It may appear to work just fine, but you shouldn't be relying on its safety.
2. Your program causes undefined behaviour by accessing memory past the end of the array. In this case, it looks like one of your str[i] = c writes overwrites the value in i.
3. C++ has the same rules as C does in this case.

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