how to search around a file for a matching string with a given one?

Question

void merr_liber()
{
  FILE *fp_merr_liber;
  FILE *fp_librat;
  
  struct merr_liber input;
  struct librat liber;
  
  char isbn[13];
 
  int zgjedhja;
  
  fp_merr_liber = fopen("librat_e_marre.txt", "ab+");
  fp_librat = fopen("librat.txt", "r");
  

  if (fp_merr_liber == NULL)
  {
    printf("\nError merr_librat.txt nuk mund te hapet\n\n");
    exit(1);
  }
  if (fp_librat == NULL)
  {
    printf("\nError librat.txt nuk mund te hapet\n\n");
    exit(1);
  }
  while (!feof(fp_librat))
  {
     printf("\nISBN: ");
     scanf("%s", isbn);
     fscanf(fp_librat, "%s", liber.isbn);
     if (unike(isbn, 13) && valide(isbn, 13) && !strcmp(isbn, liber.isbn))
     {
        strcpy(input.isbn, isbn);
        fprintf(fp_merr_liber, "%s\n", input.isbn);
        break;
     }
     if (strcmp(isbn, liber.isbn) != 0)
     {
        printf("Nuk ekziston nje liber me kete isbn.\n");
        printf("Deshironi te vazhdoni ? (1- vazhdo 0- kthehu ne menune kryesore): ");
        scanf("%d", &zgjedhja);
        
        if (zgjedhja == 1)
        {
            continue;
        }
        else
        {
            menu();
        }
     }
     printf("Gabim ne formatin e isbn, isbn ka 13 karaktere, te cilat jane unike.");
  }

  
  fclose(fp_merr_liber);
  fclose(fp_librat);
}

I have a function that gets the string isbn from the user and then compares it to the member of the structure librat which is saved into a file. I am having difficulties since my while loop is only searching throw the first row and not the entire file. The inside functions are just for formatting and do not play any role in writing or reading the file. The labels are in my native language and I hope that beside this the code is still readable. I only need one instance since the string isbn is unique

Side note: your usage of `while (!feof(fp_librat))` is [wrong](https://stackoverflow.com/questions/5431941/why-is-while-feof-file-always-wrong). You should check if reading succeeded *before* using what are "read". — MikeCAT, Jun 14 '21 at 18:26
Do you want to find all instances of the word, or just the first one found? — ryyker, Jun 14 '21 at 18:38
https://en.wikipedia.org/wiki/Knuth%E2%80%93Morris%E2%80%93Pratt_algorithm — William Pursell, Jun 14 '21 at 19:08

score 0 · Accepted Answer · edited Jun 14 '21 at 18:46

0

You're trying to get a new string as an input in every iteration of the while loop which is probably not what you want.

One thing you can do is create a different while loop and use fscanf() until the end of file is reached and compare each string gotten from the file with the string that you want to find, also don't forget to move the file position pointer to the beginning of the file after the end of file is reached.

edited Jun 14 '21 at 18:46

Andrew Truckle

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answered Jun 14 '21 at 18:41

JASLP doesn't support the IES

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@kevinhalili just use `fseek(fp_librat, 0, SEEK_SET);` – JASLP doesn't support the IES Jun 14 '21 at 18:51
I just used rewind – kevin halili Jun 14 '21 at 20:00

ryyker · Answer 2 · 2021-06-14T19:56:01.260

"I only need one instance since the string isbn is unique"

As noted, while(!feof(fp)) is always wrong

There are many ways to do this, one alternative approach is to use while(fgets(...)) {...} line by line with strstr().

The following illustration is not a complete solution, but will hopefully provide you with a starting place from which you can expand to meet your needs:

char *tok = NULL;
int len = strlen(fp_librat);
char line[MAX_LEN] = {0};//#define this elsewhere
while(fgets(line, sizeof line, fp_librat))
{
     tok = strstr(line, input.isbn)// look for search word in each line of file.
     if(tok)//captured pointer to trailing content starting at searched word
     {
             strcpy(line, tok); //places content starting at found word into buffer           
             if((line[len] == ' ')||//qualify what you have found by 
             (line[len] == '\n')||  //looking for characters that can
             (line[len] == '\t')||  //follow a string...
             (line[len] == '.')||
             (line[len] == ','))
             //there are others, but you get the idea
             {
                  line[len] = 0;//null terminate
                  //at this point the search is done.  You have confirmed that the search word
                  //is in the content searched.  
                  line[strcspn(line, " ")] = 0;// optional extract word from rest of content.
                  break; //not optional: search is finished, leave and report 'found'
             }
             else //keep looking, (found a substring, not the search string.)
     }
}
           
     break;

how to search around a file for a matching string with a given one?

2 Answers2