c++ function & array question

shaggy112 · 05-23-2001, 11:04 PM

I am working on some homework for c++ class. I am trying to pass the data from a file into an array. I am using g++ version 2.96.
When I try to compile it spits error about converting from string. Here is all below.

quote:
--------------------------------------------------------------------------------
void read_in (string &filename, string stud_id[], string fname[], string lname[], int score[], int &n) {
const int max_students = 100;
n=0;

ifstream fin(filename.c_str());
if (!fin) {
cout << "Bad file.\n";
exit(1);
}

while (fin >> stud_id[n] >> lname[n] >> fname[n] >> score[n]) {
n++;
}
} //end read_in

--------------------------------------------------------------------------------

Excerpt from main:

quote:
--------------------------------------------------------------------------------
int numval, testscore;
string inputfilename, lname, sid, fname;
case 'A': case 'a': {
cout << "Please enter file to be read: ";
cin >> inputfilename;
read_in(inputfilename, sid, lname, fname, testscore, numval);
}
--------------------------------------------------------------------------------

Error:

quote:
--------------------------------------------------------------------------------
grades.c: In function `int main ()':
grades.c:164: cannot convert `string' to `basic_string<char,
string_char_traits<char>, __default_alloc_template<true, 0> > *' for
argument `2' to `read_in (string &, basic_string<char,
string_char_traits<char>, __default_alloc_template<true, 0> > *,
basic_string<char, string_char_traits<char>,
__default_alloc_template<true, 0> > *, basic_string<char,
string_char_traits<char>, __default_alloc_template<true, 0> > *, int *,
int &)'
--------------------------------------------------------------------------------

I am obviously passing the strings by reference, as I thought I should. I did also think that string arrays always passed by ref without using &. What is wrong here?

btw. line 164 is this:
read_in(inputfilename, sid, lname, fname, testscore, numval);

Thanks a lot!

crabboy · 05-24-2001, 10:41 PM

The problem is that you have declared your read function to take arrays of strings, but you are passing just strings. Here is your code with the fix:

Code:

#include <stdlib.h>
#include <fstream.h>
#include <string>

void read_in ( const std::string filename,
               std::string stud_id[],
               std::string fname[],
               std::string lname[],
               int score[],
               int& n)
{
   const int max_students = 100;
   n=0;

   ifstream fin(filename.c_str());
   if (!fin)
   {
      cout << "Bad file.\n";
      exit(1);
   }

   while (fin >> stud_id[n] >> lname[n] >> fname[n] >> score[n])
   {
      n++;
   }

} //end read_in

int main( int argc, char * argv[] )
{
   int numval;
   int testscore[10];
   std::string inputfilename;
   std::string lname[10];
   std::string sid[10];
   std::string fname[10];

   cout << "Please enter file to be read: ";
   cin >> inputfilename;
   read_in(inputfilename, sid, lname, fname, testscore, numval);

   for ( int i = 0; i < numval; i++ )
   {
      cout << "Sid: " << sid << endl;
      cout << "lname: " << lname << endl;
      cout << "fname: " << fname << endl;
      cout << "testscore:" << testscore << endl << endl;

   } // end for
} // end main

I don't know how far along you are in the class. but your program would be much better if you passed a vector of student classes or even a vector of structs instead of the sperate arrays. This way would be cleaner and would eliminate the static sized arrays that will cause problems. You should pass the max size of the declared arrys into the read method if you do use the arrays.
You could also return the number of items found rather then pass it as a parameter.

Good Luck

Gary

NOTE: The cout statements in the loop had i indexes but they will not display in this forum. They were being interpreted as start italic.

[Edited by crabboy on 05-24-2001 at 11:45 PM]