Expert: vijayan - 11/17/2009

Question
hello sir i m trying to search a string(i.e keyword) stored in one file with the program stored into another file .But the probelm is that i want to read from file (i.e is the file of the program)line by line i.e is first line should get me line #include<stdio.h> only.So please tell me how it can happen in c++
how can we read line line from any file


#include<stdio.h>
#include<conio.h>
#include<process.h>
#include<fstream.h>
#include<string.h>
#include<dos.h>

fstream fin,filein;
int match(char *,char *);

void main()
{ clrscr();
 char ch,a[50],b[50][50],temp[20],kwrd[10];
 int i=0,j=0,tmp,flag=0,max=0,c;

fin.open("demoprg.txt",ios::in);
filein.open("tmpprg.txt",ios::out);
if(!fin ||!filein)
{ cout<<endl<<"File not exists...";
  getch();
  exit(0);
}
  cout<<endl<<"\t\t****PROGRAM IS ******"<<endl;
  while(!fin.eof())
  {   fin.get(ch);
      cout<<ch;
      filein.put(ch);
  }

  cout<<endl<<"File has been copied.....;";
  fin.close();
  filein.close();
  getch();
  clrscr();

  filein.open("keywords.txt",ios::in);
  if(!filein)
  { cout<<endl<<"file not exists......:";
    getch();
    exit(0);
  }

while(!filein.eof())
{    filein.get(ch);
   //  delay(100);
      if(ch!=' ')
      {  b[i][j]=ch;
    cout<<b[i][j];
    flag=0;
    if(max<j)
    max=j;
    j++;
  }
  else
  { if(ch==' ' && flag==0)
    { b[i][j]='\0';
      tmp=i;
      flag=1;
      i++;
      j=0;
    }
  }
}
cout<<"********\n";
cout<<max<<endl;
for(i=0;i<tmp+1;i++)
{ for(j=0;j<max+1;j++)
{ cout<<b[i][j]; }
}
filein.close();

cout<<endl<<"***Keywords ****";
fin.open("tmpprg.txt",ios::in);
 if(!fin)
 { cout<<endl<<"file not exists...:";
   getch();
   exit(0);
 }
i=0;
j=0;
int k=0;
getch();
clrscr();
while(k<tmp+1)
{ i=k;
 cout<<endl<<i<<" keyword->"<<b[i];
 while(!fin.eof())
 {  fin.get(ch);
    while(1)
    { a[j]=ch;
      j++;
      fin.get(ch);
      if(ch==' ')
      break;
    }
    a[j]='\0';
    cout<<"a[] ->"<<a;
    getch();
    j=0;
    if(strcmp(a,b[i])==0)
    cout<<endl<<"Keyword found ->"<<b[i];
 }
 fin.seekg(0);
 k++;
}

getch();
exit(0);
}
int match(char *body,char *search)
{ int chk;
 int len =strlen(body);
 int len2 =strlen(search);
 for(int p=0;p<len;p++)
 { if(body[p]==search[0])
   {   chk=1;
      for(int q=0;q<len2;q++)
  { if(body[p+q]==search[q])
     chk=1;
    else
     chk=0;
  }
    }
  if(chk)
  return 1;
  }
  return 0;
}  

Answer
These are not standard c++ headers

#include<stdio.h>
#include<conio.h>
#include<process.h>
#include<fstream.h>
#include<string.h>
#include<dos.h>

<conio.h> and <dos.h> are not, and never have been standard C headers; functions like clrscr() are not part of any standard C or C++ header. It is best to avoid their use.

The C++ headers that need to be included are

#include<cstdio>
#include<cstdlib>
#include<fstream>
#include<cstring>

If you do not want to qualify ever use of a library provided identifier with std::, you may also add

using namespace std ;


It is preferable to use a std::string instead of c-style char arrays - they are easier to use and grow and shrink as needed. see: http://www.cprogramming.com/tutorial/string.html

To read a single line from an input stream into a string, use std::getline.
see: http://www.cplusplus.com/reference/string/getline/

To read input from an input stream till eof, do not use a construct like:

while( !filein.eof() )
{    
   filein.get(ch);
   //  process ch which has just been read

   // ...
}

This has a subtle error: eof() is checked before the attempt to read, you need to check for eof() or any other error after you had tried to perform an input operation.

The fix is easy; just write

while( filein.get(ch) )
{    
   //  process ch which has just been read

   // ...
}

An example of reading a file line by line and printing it out to stdout with line numbers:

#include <string>
#include <fstream>
#include <iostream>

int main()
{
     const char* file_name = ""keywords.txt" ;
     std::ifstream file( file_name ) ; // open the file
     if( !file ) { /* error file could not be opened */ }

     std::string line ;
     int line_number = 0 ;

     while( std::getline( file, line ) )
           std::cout << ++line_number << '.' << line << '\n' ;
}

You could use the find member of std::string to search for the keyword.
see: http://www.cplusplus.com/reference/string/string/find/