当我将 a 值设置为字符串的末尾时出现分段错误

Question

我写了一个反转字符串的简单函数。我尝试不使用 char* 末尾的最后一个字符 '\0' 为交换分配临时字符。但是，它会在 *end = *str; 处报告分段错误；

谁能解释原因？

非常感谢！

#include<stdio.h>
#include<stdlib.h>
void reverse(char* str)
{
    char* end = str;
    char* i = str;
    char* j = str;
    while(*end)
        ++end;
    j = end;
    *end = *str;
    while(j > i)
    {
        *i = *j;
        ++i;
        *j = *i;
        ++j;
    }
    while(i < end)
    {
        *i = *(i+1);
        ++i;
    }
    *i = '\0';
}

void main(int argc, char* argv[])
{
    char* str_test1;
    char* str_test2;
    str_test1 = (char*) malloc(10);
    str_test2 = (char*) malloc(2);
    str_test1 = "abcdefjhi";
    str_test2 = "a";
    printf("input str1=%s, str2=%s", str_test1, str_test2);
    reverse(str_test1);
    reverse(str_test2);
    printf("output str=%s, str2=%s", str_test1, str_test2);
    free(str_test1);
    free(str_test2);
}

[在我将代码更改为以下之后，它可以工作。]

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
void reverse(char* str)
{
    char* end = str;
    char* i = str;
    char* j = str;
    while(*end)
        ++end;
    j = end;
    *end = *str;
    **--j;**
    while(j > i)
    {
        *i = *j;
        ++i;
        *j = *i;
        **--j;**
    }
    while(i < end)
    {
        *i = *(i+1);
        ++i;
    }
    *i = '\0';
}

void main(int argc, char* argv[])
{
    char* str_test1;
    char* str_test2;
    str_test1 = (char*) malloc(10);
    str_test2 = (char*) malloc(2);
    strcpy(str_test1, "abcdefjhi");
    strcpy(str_test2,"a");
    printf("input str1=%s, str2=%s\n", str_test1, str_test2);
    reverse(str_test1);
    reverse(str_test2);
    printf("output str=%s, str2=%s\n", str_test1, str_test2);
    free(str_test1);
    free(str_test2);
}

Answer 1

这并不像你认为的那样：

str_test1 = (char*) malloc(10);
str_test2 = (char*) malloc(2);
str_test1 = "abcdefjhi";
str_test2 = "a";

你可能想要这个：

str_test1 = (char*) malloc(10);
str_test2 = (char*) malloc(2);
strcpy(str_test1, "abcdefjhi");
strcpy(str_test2, "a");

或者这个：

char str_test1[10] = "abcdefjhi";
char str_test[2]   = "a";

您当前拥有的分配内存，然后用指向只读字符串文字的指针覆盖指向您分配的内存的指针，这是获得段错误的好方法。

以上任何一种替换都会给你一个可写的字符串，你可以安全地反转它。