Demonstrate peek() in ifstream

 

#include <iostream>
#include <fstream>
#include <cctype>
using namespace std;

int main()
{ 
  char ch;
  ofstream out("test", ios::out | ios::binary);

  if(!out) {
    cout << "Cannot open output file.\n";
    return 1;
  }

  char str[80], *p;
 
  out << 123 << "this is a test" << 23;
  out << "Hello there!" << 99 << "sdf" << endl;
  out.close();
  
  ifstream in("test", ios::in | ios::binary);

  if(!in) {
    cout << "Cannot open input file.\n";
    return 1;
  }

  do {
    p = str;
    ch = in.peek();                    
    if(isdigit(ch)) {
      while(isdigit(*p=in.get())) 
         p++; 
      in.putback(*p); 
      *p = '\0';                        
      cout << "Integer: " << atoi(str);
    }
    else if(isalpha(ch)) {              
      while(isalpha(*p=in.get())) p++;
      in.putback(*p);                   
      *p = '\0';                        
      cout << "String: " << str;
    }
    else 
      in.get();                        
    cout << '\n';
  } while(!in.eof());
  
  in.close();
  return 0;
}

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Demonstrate peek() in ifstream : File Read « File « C++

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