使用fgets和strstr在C中查找和计数字符串

Question

I'm trying to work on an assignment. The idea is to get an array of strings, and a file stream. I need to look for those strings in the file, and count the occurrence of these strings.

I think I've got the basic loop down. The only problem is that, when I find a string in the line, I want to search for that string again (in case of more than one occurrence) by starting from 1 + the position where the found string starts.

#define LINE_MAX_CHARS 1000

// n = number of strings to be found
// **strings = array of strings to look for in file
void count_occurrences (int n, FILE *file, char **strings) {
  char str[LINE_MAX_CHARS]; // buffer
  int count = 0;
  while (fgets(str, LINE_MAX_CHARS, file) !=  NULL){ // for each line
      for (int i = 0; i < n; i++){ // for each word in line
          char *found; 
          found = (strstr(str, (*(strings + i)))); // search line
          if (found != NULL){ // if word found in line
            // here, I want str (the buffer) to have its 0-th element to be the element at (found + 1), 
            // and the 1-st element to be (found + 2) and so on...
            i--; // to look for same word in the rest of the line
            count = count + 1;
          }
      }
  }
}

Another problem is that I have no way of testing my code. I'm just given a test program that runs and tells me whether or not my code is producing the correct output.

I am REQUIRED to use fgets and strstr.

Suggestions?

Answer 1

strstr(str, strings[i]) Returns a pointer to a position in the string. You should be able to increment that pointer ( str++ ) and pass it straight back into strstr() in a loop, incrementing count each time, finishing the loop if strstr() returns NULL or str hits the null character.

It should look something like this. I've not tested this; but since this is your homework, if it doesn't work/compile quite right, I'm going to leave it to you to debug. That means I won't have done all the work for you...

;-)

void count_occurrences (int n, FILE *file, char **strings) {
  char str[LINE_MAX_CHARS];
  int count = 0;

  while (fgets(str, LINE_MAX_CHARS, file) !=  NULL){
    for (int i = 0; i < n; i++){
      char *pos = str;

      while(((pos = strstr(pos, strings[i]) != NULL) && *pos != '\n') {
        count++;
        pos++;
      }
    }
  }
}

Answer 2

To count every occurrence of strings[i] in the current line, you have to use a loop and you have to let strstr start at least one position after the last occurrence. See the following code:

#define LINE_MAX_CHARS 1000

// n = number of strings to be found
// **strings = array of strings to look for in file
void count_occurrences (int n, FILE *file, char **strings) {
   char str[LINE_MAX_CHARS]; // buffer
   int count = 0;
   while (fgets(str, LINE_MAX_CHARS, file) !=  NULL){ // for each line
      for (int i = 0; i < n; i++){ // for each word in line
          char *found = str;
          do { 
            found = strstr(found, strings[i]); // search line
            if (found != NULL){ // if word found in line
              count = count + 1;
              found++;
            }
          }
          while (found)
      }
   }
}