Question

我很难弄清楚为什么我的代码没有遍历 if 语句直到找到正确的字符。

#include <stddef.h>
#include <stdio.h>

char * my_strstr(char * param_1, char * param_2) {
    int i;
    int j;
    for (i = 0; param_1[i] != '\0'; i++) {
      printf("this is a loop for j %c\n", param_1[i]);
      for (j = 0; param_2[j] != '\0'; j++) {
        printf("this is a loop for j %c\n", param_2[j]);
        if (param_1[i] == param_2[j]) {
          printf("figuring out this %c\n", param_1[i]);
          j++;
          i++;
          return &param_1[i];
          printf("figuring out this %c\n", param_1[i]);
        }
      }
    }
  }

int main() {
  char * param_1 = "hello";
  char * param_2 = "ello";

  printf("This is the string %s \n", my_strstr(param_1, param_2));

  return 0;
}

Answer 1

我在下面粘贴了您的代码，并进行了一些编辑和评论，希望能有所帮助。

#include <stddef.h>
#include <stdio.h>

char * my_strstr(char * param_1, char * param_2) {
    int i;
    int j;
    for (i = 0; param_1[i] != '\0'; i++) {

      // this should say "loop for i" shouldn't it?
      printf("this is a loop for j %c\n", param_1[i]);

      // use a flag to determine if you have found a match or not
      int found = 1;

      for (j = 0; param_2[j] != '\0'; j++) {

        /* you actually want to compare param_1[i + j] == param_2[j] here
           (respecting bounds of course). */
         if (! param_1[i + j] || param_1[i + j] != param_2[j]) {
           found = 0;
           break;
          }

        printf("this is a loop for j %c\n", param_2[j]);

        /* i don't understand what the following code was meant to do but you will
           rarely want to increment i and j outside of the for ()

        if (param_1[i] == param_2[j]) {
          printf("figuring out this %c\n", param_1[i]);
          j++;
          i++;
          return &param_1[i];
          printf("figuring out this %c\n", param_1[i]);
        }
        */
      }

      // here you want to check if you found it, and return if so.
      if (found) {
        return &param_1[i];
      }
    }
    // need a default for if it is never found:
    return NULL;
  }

int main() {
  char * param_1 = "hello";
  char * param_2 = "ello";

  printf("This is the string %s \n", my_strstr(param_1, param_2));

  return 0;
}

使用 C 在干草堆中找针

1 个答案: