#include <string>
#include <stdio.h>
#include <fstream>
#include <iostream>
using namespace std;

int main()
{
   char charin[80];
   char ch0[4]="JJU";
   bool match;
   ifstream fin("char.dat");
   ifstream fout("out.dat");
   int length1 = strlen(ch0);
   cout << "length of ch0=" << length1 << endl;
   while (fin >> charin) {
      int length2 = strlen(charin);
      cout <<  charin << "  ,strlength=" << length2<< endl;
      if( length1 != length2 ) continue;
      match = true;
      for (int j=0; j<length1; j++) {
        if ( charin[j] != ch0[j]) match = false;
      }
   if (match) cout << "match found : " << charin << endl;
   }

   fin.close();
   fout.close();
   return 0;
}
----------------------char.dat---------------------------
FiTR  f g
JJU 1.2
jjj
hhh 8
endend 999hhh 8
endend 999hhh 8
endend 999
-------------------------output-------------------------------------
$ ./a.exe
length of ch0=3
FiTR  ,strlength=4
f  ,strlength=1
g  ,strlength=1
JJU  ,strlength=3
match found : JJU
1.2  ,strlength=3
jjj  ,strlength=3
hhh  ,strlength=3
8  ,strlength=1
endend  ,strlength=6
999hhh  ,strlength=6
8  ,strlength=1
endend  ,strlength=6
999hhh  ,strlength=6
8  ,strlength=1
endend  ,strlength=6
999  ,strlength=3
------------------------------------