Thread: Read a file

Hello,

I'm just curious as I'm new to programming. Whenever I want to read a file and get strings from the file. Say I have a file like this:

ExampleFile.txt:
Name: John Smith
Age: 16
Address: example, address, 12345
... and so on

And the way i read the file and retrieve the information, I usually do it by reading the file line by line and tokenise each string. So I'll get an array of words. So my question is, is there a better way to do it?

That is going to depend entirely upon what you're trying to achieve.

The example you've given would be a poor candidate for tokenizing since you may well want the person's name and address as intact strings. In that case you could (for example) write a parser that see the word "Name:" and copies the right side of the string into a struct that holds the individual's information. "Age" could be converted to an integer and stored in the same struct... and so on.

What you do with filed data and how you manipulate it is going to be dictated by the needs of the application you are working on.

Originally Posted by AndrewHunter

Also, I'm sure Tater will be back along to post an example.

Hey, it's your turn...

The way you are presently doing it, breaking the lines into tokens, is the only way to do it. I think thats what C is all about, that you can analyze things down to the subatomic level. I dont think there is a way to token it while reading it, so you got to do all that stuff once you have read the file. Its tedious and hard but at least it can be done. Some languages cant even do that.

Perhaps, it didnt come out right. I was trying to say, "the easiest way" is how he is doing it, without having to create binaries and arrays of structures, etc. I was just trying to start some interesting discussion on the virtues of C and its ability to parse coz it is very powerful. Maybe I didnt say it right but I wasnt trying to mislead anyone.

Originally Posted by Linux Trojan

The way you are presently doing it, breaking the lines into tokens, is the only way to do it. I think thats what C is all about, that you can analyze things down to the subatomic level. I dont think there is a way to token it while reading it, so you got to do all that stuff once you have read the file. Its tedious and hard but at least it can be done. Some languages cant even do that.

Oh Bullsmut!

Ok... he has an address line "123 AnyStreet, Anytown, Canada, A1A 1A1" ... how does toeknizing that string into words to anything except destroy the meaning of the data? He wants that as one contiguous string, not a list of words.

Originally Posted by Linux Trojan

Perhaps, it didnt come out right. I was trying to say, "the easiest way" is how he is doing it, without having to create binaries and arrays of structures, etc. I was just trying to start some interesting discussion on the virtues of C and its ability to parse coz it is very powerful. Maybe I didnt say it right but I wasnt trying to mislead anyone.

How much simpler do you want it?

Code:

//random access file demo
#include <stdlib.h>
#include <stdio.h>
#include <time.h>
#include <ctype.h>
#include <string.h>

#define FNAME "random.dat"

// test data struct
struct t_Record
  { int randnum;
    char word[16]; }
  Record;



///////////////////////////////////////////////////////
// Random Access File Handlers
//

// open or create the file
FILE *FileOpen(char* Filename)
  { FILE* pFile;
    pFile = fopen(Filename,"rb+");
    if (!pFile)
      pFile = fopen(Filename,"wb+");
    return pFile; }


// Write a record to the file
int WriteRecord(FILE *File, int RecNum)
  { if( fseek(File, RecNum * sizeof(Record), SEEK_SET) == 0 )
      if ( fwrite(&Record,sizeof(Record),1,File) )
        return 1;
    return 0; }


// read a record from the file
int ReadRecord(FILE *File, int RecNum)
  { if( fseek(File, RecNum * sizeof(Record), SEEK_SET) == 0 )
      if ( fread(&Record,sizeof(Record),1,File) )
        return 1;
    return 0; }



////////////////////////////////////////////////////////
// this is for demonstration purposes only
// you would not do this in a real program
void InitFile(FILE* File)
 { int x, y;
   memset(&Record,sizeof(Record),0);
   for (x = 0; x < 1000; x++)
      { Record.randnum = rand();
        for (y = 0; y < ((Record.randnum % 15) + 1); y++)
          Record.word[y] = (rand() % 26) + 'a';
        Record.word[y] = 0;
        if (! WriteRecord(File,x))
          printf("Oh drat!");  } }
 

 
//////////////////////////////////////////////////////////
// program mains
//
int main (void)
  { FILE *File;
    int Quit = 0;
    int Rec = 0; // record number

    srand(time(NULL));

    File = FileOpen(FNAME); 
    if (!File)
      { printf("Curses foiled again!\n\n");
        exit(-1); }

    // write out 1000 test records  
    printf("Create a new file? (y/n)  ");
    if ( toupper( getchar() ) == 'Y')
      InitFile(File);
  
    // lets peek
    do
      { printf("Enter a record number (0 - 999) to load : ");
        if (! scanf("%d",&Rec) )
          Quit = 1;  // enter any letter to quit
        else 
          { // read and display the record 
           if (! ReadRecord(File,Rec) ) 
              printf("Could not read record %d\n",Rec);
            else
              { printf("-----\n");
                printf("Record Number : %d\n",Rec);
                printf("Number Value  : %d\n",Record.randnum);
                printf("Record Name   : %s\n",Record.word);
                printf("-----\n"); 
                getchar();
                printf("Do you want to rename this record (y/n)? ");
                if ( toupper( getchar() ) == 'Y')
                  { printf("Enter a new name : ");
                    if ( scanf("%s",Record.word) )
                      WriteRecord(File,Rec);  } } }
      } while (! Quit); 


    fclose(File);
    return 0; }

Originally Posted by Linux Trojan

Perhaps, it didnt come out right. I was trying to say, "the easiest way" is how he is doing it, without having to create binaries and arrays of structures, etc. I was just trying to start some interesting discussion on the virtues of C and its ability to parse coz it is very powerful. Maybe I didnt say it right but I wasnt trying to mislead anyone.

Actually, the whole point of THIS thread is to answer the OP's question.

If you want to start an interesting discussion on parsing files... start your own thread, don't hijack someone else's.

Tater: Thats alot of code to analyze, and I will in time. But for now, I just thought that for a newbie, it would be easier to break the info into tokens and then just use STRCAT to sew it all back up again. I stand corrected. I gotta run!