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read text file using c/c++

Posted on 2007-07-24
Medium Priority
Last Modified: 2010-10-05
Hi All,
I have to read text file which has data in following manner,
2345  zxc  123344 abchfdfdfdg
I need to read fixed length and store same into variable,
Say first 6 character, then next 5 and so on&
This will also include spaces.

Whats the best way to do this??
Is fgetc is right way to do this?

Please suggest.

Thanks in advance.


Question by:vjabhi
LVL 53

Expert Comment

ID: 19554034
Do a getline, and then process the line you got. Since you want to split it up at fixed indexes, that shouldn't be too hard ... substr should help :


Don't forget to check out the example code at the bottom of those pages.

For reading a file, check out this tutorial :

LVL 39

Accepted Solution

itsmeandnobodyelse earned 100 total points
ID: 19554193
You might use a structure that exactl ymatches the line:

struct Record
     char sz1[6];
     char sz2[5];

Then you could read like

     Record rec;
     ifstream ifs("data.txt");
     string line;
     while (getline(ifs, line))
           istringstream iss(line);
           iss.read((char*)&rec, sizeof(Record));
           if (!iss)
               return;  // error
           rec.sz1[sizeof(rec.sz1)-1] = '\0'; // terminate string
           rec.sz2[sizeof(rec.sz2)-1] = '\0'; // terminate string
           v.push_back(rec);  // put record to an array

Regards, Alex
LVL 46

Assisted Solution

by:Kent Olsen
Kent Olsen earned 100 total points
ID: 19555428
A third option is to use fscanf() to read the line a split the tokens.

2345  zxc  123344 abchfdfdfdg
I need to read fixed length and store same into variable,
Say first 6 character, then next 5 and so on&

  char F1[7];   // size plus 1
  char F2[6];   // size plus 1
  char F3[8];   // size plus 1
  char F4[12]; // size plus 1

  fscanf (Input, "%6.6s%5.5s%8.8s%11.11s", F1, F2, F3, F4);

Good Luck,


Expert Comment

ID: 19591780
You could read 1 character at a time and loop through until you find what you want..

#include <cstring>
#include <fstream.h>
using namespace std;

string readCharacters(int charStart, int charEnd, char* filename)
   string ret;
   ifstream file (filename); // open file stream for reading using filename specified
   if ( !file.is_open() || !file.good() )
      // Error has occured opening file: Handle it.
      char c;
      for (int a = 0; a < charEnd; a++)
         c = (char)file.get(); // Get the character at this point in file
         if ( a > charStart && a < charEnd ) // if the character
            ret += c; // append character to string
   return ret;

That is roughly how you could do it in C++, not sure if it works as I haven't tested it.
You would use this function to get characters from charStart to charEnd in the file specified by filename.. i.e.

string a = readCharacters(0,4,"C:\\file.txt");
string b = readCharacters(5,8,"C:\\file.txt");

Expert Comment

ID: 19606464
a simple program to read file line by line
        #include <stdio.h>
       #include <stdlib.h>

       int main(void)
            FILE * fp;
            char * line = NULL;
            size_t len = 0;
            ssize_t read;
            fp = fopen("file.txt", "r");
            if (fp == NULL)
            while ((read = getline(&line, &len, fp)) != -1) {
                 printf("Retrieved line of length %zu :\n", read);
                 printf("%s", line);
            if (line)
            return EXIT_SUCCESS;

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