总线错误故障排除 [英] Bus error troubleshooting

问题描述

我试图扭转一个字符串。

I am trying reverse a string.

这是code我尝试：

#include<stdio.h>
#include<string.h>

int main(){
    char *c="I am a good boy";
    printf("\n The input string is : %s\n",c);
    printf("\n The length of the string is : %d\n",strlen(c));
    int i,j;
    char temp;
    int len=strlen(c);
    for(i=0,j=len-1;i<=j;i++,j--)
    {
            temp=c[i];
            c[i]=c[j];
            c[j]=temp;
    //printf("%c\t%c\n",*(c+i),*(c+(len-i-1)));
    }
    printf("\n reversed string is : %s\n\n",c);
}

在code输出总线错误：10

但是，如果我重写同一code为：

But if I rewrite the same code as:

int main(void)
{
    char *str;
    str="I am a good boy";
    int i,j;
    char temp;
    int len=strlen(str);
    char *ptr=NULL;
    ptr=malloc(sizeof(char)*(len));
    ptr=strcpy(ptr,str);
    for (i=0, j=len-1; i<=j; i++, j--)
    {
        temp=ptr[i];
        ptr[i]=ptr[j];
        ptr[j]=temp;
    }
    printf("The reverse of the string is : %s\n",ptr);
}

这工作完全正常。

It works perfectly fine.

为什么第一个code抛出总线错误或段故障？

Why is the first code throwing bus error or segmentation fault?

推荐答案

因为在许多（如果不是大多数或所有现代）C编译器，字符串在只读存储器分配时发生总线错误。

The bus error occurs because in many (if not most or all modern) C compilers, string literals are allocated in read-only memory.

您正在倒车的地方字符串。在你的第一个code段你试图写入一个字符串。这不是一个好主意。

You are reversing the string in place. In your first code snippet you are trying to write into a string literal. Not a good idea.

在第二种情况下，你malloc分配它把它堆的字符串。现在是安全的，扭转地方的字符串。

In the second case, you malloc'd a string which put it on the heap. It is now safe to reverse that string in place.

附录

要谁问段错误与总线错误的评议，这是一个很大的问题。我已经看到两者。这是在Mac上总线错误：

To the commenter who asked about segfaults versus bus errors, that is a great question. I have seen both. Here is a bus error on a mac:

$ cat bus.c 
char* s = "abc"; int main() {s[0]='d'; return 0;}

$ gcc --version bus.c && ./a.out
i686-apple-darwin10-gcc-4.2.1 (GCC) 4.2.1 (Apple Inc. build 5659)
Copyright (C) 2007 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Bus error

在其他操作系统/编译器，你可能确实得到段错误。

On other operating systems/compilers you may indeed get a segfault.

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