ifstream fin( "1.txt" ); 
ifstream fim( "2.txt" ); 
ifstream fib( "3.txt" ); 

string mlstr; 
string mainstr; 
string str_name; 

do 
{ 
getline( fib, str_name ); 
getline( fin, mainstr ); 
getline( fim, malstr ); 

somefunction(str_name, mainstr, malstr); 
} 

while(!fib.eof() &&!fin.eof() &&!fim.eof());