使用malloc替換字符串中子字符串的C函數 - 無字符串函數

Question

現在我可以用nonchalant替換給定字符串中的indifferent這個詞，但是我需要使此函數具有動態性，因此indifferent可以用任何單詞替換。我知道我需要使用malloc來創建一個新的數組，這個數組將會保留我的原始字符串，但是對於如何使用malloc還沒有很好的理解，請解釋如何在這種情況下正確使用malloc。謝謝。

#include <stdio.h> 
#include <stdlib.h> 

int findPosition(char string[], char sub[]) { 
    int i = 0; 
    int j = 0; 
    int f = 0; 

    for (i = 0; string[i] != '\0'; i++) { 
     if (sub[j] == string[i]) { 
      if (sub[j + 1] == '\0') { 
       f = 1; 
       break; 
      } 
      j++; 
     } else 
      j = 0; 
    } 
    if (f == 1) { 
     return i - j; 
    } 
    return -1; 
} 

int findLength(char sub[]) { 
    int i = 0; 

    for (i = 0; sub[i] != '\0'; i++) { 

    } 
    return i; 
}; 

void replaceWord(char string[], char sub[], char replace[]) { 
    int i = 0; 
    int j = 0; 
    int p = findPosition(string, sub); 
    int l = findLength(sub); 
    int k = p + l - 1; 

    for (i = p; i < k; i++) { 
     string[i] = replace[j]; 
     j++; 
    } 
    while(string[k] != '\0') { 
     string[k] = string[k + 1]; 
     k++; 
    } 
} 

int main(int argc, const char *argv[]) { 
    char stringArray[120] = "\"Mr.Fay, is this going to be a battle of wits?    \"" 
          "\t\"If it is,\" was the indifferent retort, \"" 
          "you have come unarmed!\""; 

    replaceWord(stringArray, "indifferent", "nonchalant"); 

    int i = 0; 
    while (stringArray[i] != '\0') { 
     printf("%c", stringArray[i]); 
     i++; 
    } 
    return 0; 
}; 

Answer 1

可以使用malloc爲新的字符串分配內存，你用另一個詞替換一個單詞的每一次出現：

#include <stdio.h> 
#include <stdlib.h> 

/* use a local implementation of the string functions: */ 
size_t my_strlen(const char *s) { 
    size_t len; 
    for (len = 0; s[len] != '\0'; len++) 
     continue; 
    return len; 
} 
void *my_memcpy(void *dest, const void *src, size_t n) { 
    size_t i; 
    for (i = 0; i < n; i++) { 
     ((unsigned char*)dest)[i] = ((unsigned char*)src)[i]; 
    } 
    return dest; 
} 
char *my_strdup(const char *s) { 
    size_t n = my_strlen(s) + 1; 
    char *p = malloc(n); 
    if (p) my_memcpy(p, s, n); 
    return p; 
} 
char *my_strstr(const char *s1, const char *s2) { 
    for (;; s1++) { 
     for (size_t i = 0;; i++) { 
      if (s2[i] == '\0') return s1; 
      if (s1[i] != s2[i]) break; 
     } 
     if (*s1 == '\0') return NULL; 
    } 
} 

char *replaceWord(const char *str, const char *s1, const char *s2) { 
    char *res = my_strdup(str); /* return value is always allocated */ 
    char *p, *q; 
    size_t offset = 0; 
    size_t len = my_strlen(str); 
    size_t len1 = my_strlen(s1); 
    size_t len2 = my_strlen(s2); 

    if (len1 == 0) 
     return res; 

    while ((p = my_strstr(res + offset, s1)) != NULL) { 
     offset = p - res; 
     if (len1 == len2) { 
      /* no need to reallocate, replace in place */ 
      my_memcpy(res + offset, s2, len2); 
     } else {     
      /* allocate a new array with the adjusted length */ 
      q = malloc(len + len2 - len1 + 1); 
      /* copy the beginning of the string */ 
      my_memcpy(q, res, offset); 
      /* copy the replacement string */ 
      my_memcpy(q + offset, s2, len2); 
      /* copy the remainder of the string, and the final '\0' */ 
      my_memcpy(q + offset + len2, res + offset + len1, len - offset - len1 + 1); 
      /* free the previous string */ 
      free(res); 
      res = q; 
     } 
     /* search for matches from the end of the replacement */ 
     offset += len2; 
    } 
    return res; 
} 

int main(int argc, const char *argv[]) { 
    char stringArray[120] = "\"Mr.Fay, is this going to be a battle of wits?    \"" 
          "\t\"If it is,\" was the indifferent retort, \"" 
          "you have come unarmed!\""; 

    char *p = replaceWord(stringArray, "indifferent", "nonchalant"); 
    printf("%s", p); 
    free(p); 
    return 0; 
}