c-为什么我会出现消息分段错误

Question

使用C，我试图实现一个根据关键字string_word将word转换为mutated_word的函数。例如：当word是"HE"时，使用密钥"QWERTYUIOPASDFGHJKLZXCVBNM"，变异的单词应该变成"IT"。但它不断给分割带来错误，不确定如何改进。

#include <cs50.h>
#include <stdio.h>
#include <string.h>
int main(void) {
string word = "HE" ;
string string_word = "QWERTYUIOPASDFGHJKLZXCVBNM";
char mutated_word[strlen(word)]; 

for (int i = 0; word[i] != ''; i++) {
string_word[(int)word[i] - 65] = mutated_word[i];
}

printf("%s", mutated_word);
}

Answer 1

1. 您需要用null字符终止新字符串
2. 你的数组太小
3. 使用正确的索引类型(int不是正确的类型(
4. 检查字符是否为字母。如果没有决定要做什么(在我的例子中，我将所有字母转换为大写，其他字符保持原样(
5. 不要使用幻数。使用'A'代替65
6. 你的作业是错误的，你实际上想要的是正好相反的东西
7. 它不适用于所有字符编码

#include <ctype.h>
#include <stdio.h>
int main (void) 
{
string word = "HE" ;
string string_word = "QWERTYUIOPASDFGHJKLZXCVBNM" ;
char mutated_word [strlen(word) + 1]; 

size_t i;
for (i = 0; word[i] != ''; i++)
{
if(isalpha((unsigned char)word[i]))
{
mutated_word[i] = string_word[toupper((unsigned char)word[i]) - 'A'];
}
else
{
mutated_word[i] = word[i];
}
}
mutated_word[i] = 0;

printf("%s", mutated_word); 
}

https://godbolt.org/z/4zqq98Y3n

让它更便携：

#include <ctype.h>
#include <stdio.h>
#include <string.h>
#include <stddef.h>
ptrdiff_t findIndex(const char ch, const char * restrict dict)
{
char *result = strchr(dict, ch);
if(!result) return -1;
return result - dict;
}
int main (void) 
{
string word = "He124" ;
string string_word = "QWERTYUIOPASDFGHJKLZXCVBNM" ;
string dict = "ABCDEFGHIJKLMNOPQRSTUVXYWZ";
ptrdiff_t index;
char mutated_word [strlen(word) + 1]; 

size_t i;
for (i = 0; word[i] != ''; i++)
{
if(isalpha((unsigned char)word[i]))
{
index = findIndex(toupper((unsigned char)word[i]), dict);
}
else index = -1;
mutated_word[i] = index == -1 ? word[i] : string_word[index];
}
mutated_word[i] = 0;

printf("%s", mutated_word); 
}

https://godbolt.org/z/KW8TxxEvq

Answer 2

由于赋值顺序错误，程序崩溃：string_word[(int)word[i] - 65] = mutated_word[i];正试图修改具有未定义行为的字符串文字。还要注意，对于null终止符，目标字符串必须长1字节，必须显式设置。

这里有一个更便携的版本：

#include <ctype.h>
#include <stdio.h>
#include <string.h>
int main(void) {
const char *word = "HE";
const char *normal_word = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
const char *string_word = "QWERTYUIOPASDFGHJKLZXCVBNM";
char mutated_word[strlen(word) + 1]; 
unsigned char c;
const char *p;
size_t i;
for (i = 0; (c = word[i]) != ''; i++) {
if (isupper(c) && (p = strchr(normal_word, c)) != NULL) {
c = string_word[p - normal_word];
} else
if (islower(c) && (p = strchr(normal_word, toupper(c))) != NULL) {
c = string_word[p - normal_word];
c = tolower(c);
}
mutated_word[i] = c;
}
mutated_word[i] = '';

printf("%sn", mutated_word); 
return 0;
}