How to do Lexical analysis for c/c++ source file?

[abhisheknayak9]

i have c++ code for Lexical analysis to get result of Expression/String as input and produces output as list of tokens that are: Total Identifier, Total Constants, Total Literals, Total Keywords, Total Operators, Total Delimiters, Invalid Tokens & Used Tokens.
So, i want to know same for a C/C++ file, then how to do?

How am passing the expression for analysis as below:
void main()
{
clrscr();
char mstr[50];
printf("\n\n\tEnter String: ");// Here i want file as input
gets(mstr);
Lex_Ana oblex(mstr);//Here how to pass all lines to analysis
oblex.Find_Lex();
oblex.Rem_Dup();
oblex.Sep_Val();
oblex.Display();
getch();
}

i tried like below:

void main()
{
clrscr();
ifstream indata;
char file_name[40], *mainStr,*ch;
printf("\n\n\tEnter File name: ");
gets(file_name);
indata.open(file_name);
if(indata==NULL)
{
perror("Error while opening the file.\n");
exit(EXIT_FAILURE);
}
else
{
while(!indata.eof())
{
getline(indata,ch);
strcat(mainStr,ch);
}
Lex_Ana oblex(mainStr);
oblex.Find_Lex();
oblex.Rem_Dup();
oblex.Sep_Val();
oblex.Display();
indata.close();
}
getch();
}
But it not working..
Any help would be appreciated..