how to find coomon data in 3 files without rewind..

after the pointed comment
i dont know from what file the smallest belongs to
i dont know in what two files i got the equality
so i could write it somewhere and go the the next line of the "smallest" file
??

Code:

---

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define false 0
#define true 1

char* equal(char*f1,char*f2,char*f3);
  char* smallest(char*f1,char*f2,char*f3);
int main()
{

        FILE *file1,*file2,*file3;
       
        char f1[20];
        char f2[20];
        char f3[20];
        char* small;
    char* equall;       
        file1=fopen("c:\\1.txt","r");
        file2=fopen("c:\\2.txt","r");
        file3=fopen("c:\\3.txt","r");
        fscanf(file1,"%9s",f1);
        fscanf(file2,"%9s",f2);
        fscanf(file3,"%9s",f3);
        small=smallest(f1,f2,f3);
        equall=equal(f1,f2,f3); //how to continue after this point
                                             
        fclose(file1);
        fclose(file2);
        fclose(file3);
        return 0;
}

char* smallest(char*f1,char*f2,char*f3)
{

        char* pLowest = f1;
    if(strcmp(pLowest, f2) > 0)
      pLowest = f2;
      if(strcmp(pLowest, f3) > 0)
      pLowest = f3;
      return pLowest;
}

  char* equal(char*f1,char*f2,char*f3)
  {
    if(strcmp(f1,f3)==0)
        {
      return f1;
        }
    if(strcmp(f2,f3)==0)
        {
      return f2;
        }
          return NULL;
  }

---

So, you need a function that actually tells you which file to read next, when you have three sets of SSN.

And of course, you need to do a loop of some sort.

--
Mats

how to return the file in this function
how to know what file is the smallest string
??

Code:

---


char* smallest_file(char*f1,char*f2,char*f3,FILE* file1,FILE* file2,FILE* file3)
{

        char* pLowest = f1;
    if(strcmp(pLowest, f2) > 0)
      pLowest = f2;
      if(strcmp(pLowest, f3) > 0)
      pLowest = f3;
      return pLowest;
}

---

is there any shorter way then

Code:

---

char* smallest_file(char*f1,char*f2,char*f3,FILE* file1,FILE* file2,FILE* file3)
{

        char* pLowest = f1;
    if(strcmp(pLowest, f2) > 0)
      pLowest = f2;
      if(strcmp(pLowest, f3) > 0)
      pLowest = f3;
          if(strcmp(f1,pLowest)==0)
          {
                  return file1;
          }
      if(strcmp(f2,pLowest)==0)
          {
                  return file2;
          }
          if(strcmp(f3,pLowest)==0)
          {
                  return file3;
          }

}

---

Well, I suppose you could write a function that updates the lowest string(s) by reading from the relevant file, rather than making a function that returns the file wanted.

--
Mats

you say to write a function that updates the lowest string(s) by reading from the relevant file.
but i have to know from what file the lowest string came from.

so i cant understand how i can manage doing what you told me
without building such function?

If you keep the files and the strings in the same order at all times, you can determine if the value from file X needs updating, and read the file.

--
Mats

you say
build some how that you could know which file to update each time

but its too abstract
what sub operations i need to build?

Shouldn't need many sub-operations. Just string compare and fscanf() or something like that, and a few if-statements.

I just hacked one up in about 13 lines of code, with 5 if-statements (including finding the lowest one).

--
Mats

ok here is the comparing part

Code:

---

char* smallest(char*f1,char*f2,char*f3,FILE* file1,FILE* file2,FILE* file3)
{

        char* pLowest = f1;
    if(strcmp(pLowest, f2) > 0)
      pLowest = f2;
      if(strcmp(pLowest, f3) > 0)
      pLowest = f3;
      return pLowest;
}

---

here is the scanf part

Code:

---

      fscanf(file1,"%9s",f1);
        fscanf(file2,"%9s",f2);
        fscanf(file3,"%9s",f3);

---

for what reason i need to use
"a few if-statements"

You need if-statments to determine if you need to read from the file or not (if you already have a value higher than the lowest, you should not read the file).

--
Mats

ok i tried to write it
but how to know which string is the smallest and which file it belongs to
without writing the previous function that i showed
??

Code:

---

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define false 0
#define true 1

char* equal(char*f1,char*f2,char*f3);
  char* smallest(char*f1,char*f2,char*f3);
int main()
{

        FILE *file1,*file2,*file3;
       
        char f1[20];
        char f2[20];
        char f3[20];
        char* small;
    char* equall;       
        file1=fopen("c:\\1.txt","r");
        file2=fopen("c:\\2.txt","r");
        file3=fopen("c:\\3.txt","r");

        while(fgetc(f1)!=EOF)||(fgetc(f2)!=EOF)||(fgetc(f1)!=EOF))
        {
          fscanf(file1,"%9s",f1);
          fscanf(file2,"%9s",f2);
          fscanf(file3,"%9s",f3);
          small=smallest(f1,f2,f3);

          equall=equal(f1,f2,f3);
        }
        fclose(file1);
        fclose(file2);
        fclose(file3);
        return 0;
}

char* smallest(char*f1,char*f2,char*f3,FILE* file1,FILE* file2,FILE* file3)
{

        char* pLowest = f1;
    if(strcmp(pLowest, f2) > 0)
      pLowest = f2;
      if(strcmp(pLowest, f3) > 0)
      pLowest = f3;
      return pLowest;
}

  char* equal(char*f1,char*f2,char*f3)
  {
    if(strcmp(f1,f3)==0)
        {
      return f1;
        }
    if(strcmp(f2,f3)==0)
        {
      return f2;
        }
          return NULL;
  }

---

how to continue??

how to combine those parts

How about using a dynamically allocated array of structs whose elements are: SSN, current file number and a count. SSNs whose count equals 3 are present in all of the files. Just my 2c.