为什么我会有一个消息分割错误？

Question

使用C，我试图实现一个函数，该函数根据键word将mutated_word转换为string_word。当word是"HE"时，用键"QWERTYUIOPASDFGHJKLZXCVBNM"，mutated_word应该变成"IT"。但它一直存在分割错误，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] != '\0'; i++) {
        string_word[(int)word[i] - 65] = mutated_word[i];
    }
    
    printf("%s", mutated_word);
}

Answer 1

需要终止新字符串的character.

• Your数组太小，，

1. ，使用正确的索引类型(int不是正确的)
2. ，检查字符是否是字母。如果不决定该做什么(在我的示例中，我将所有字母转换为大写字母，其他字符将保留原样)
3. 不使用魔术数字。使用'A'
4. Your赋值代替65是错误的，您实际上想要的是相反的东西。
5. 它将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] != '\0'; 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

为了使它更便携：

#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] != '\0'; 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

程序崩溃是因为分配顺序不对：string_word[(int)word[i] - 65] = mutated_word[i];试图修改字符串文本，该字符串具有未定义的行为。还请注意，空终止符的目标字符串必须长1字节，必须显式设置该字符串。

下面是一个更可移植的版本：

#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]) != '\0'; 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] = '\0';
   
    printf("%s\n", mutated_word); 
    return 0;
}

Answer 3

这是因为您超过了string_word[]的大小，请注意，在每个示例中，'Z'-65 == 25比(int)strlen(string_word)大