File Input Error Help

[kazack]

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

enum Triangles{Scale ne,Isosceles,Eq ualateral,Inval id,Hold};
Triangles Entered = Hold;


void NotValid(int, int, int);
void Equal(int,int,i nt);
void Isos(int,int,in t);
void triangle(int,in t,int,int);

void main()
{
ifstream inData;
int sidea;
int sideb;
int sidec;

char* filename;
// I have 2 options here char* filename = "c:\filenam e";
// or const char* filename ="c:\filenam e";
//either one will work when checking for file existance.
// but can not use it with a cin statement below.

cout << "Please Enter The Data File: ";
cin >> filename;
//the above line does not work I have tried numerous
//things and can not figure out how to get it to work.
//I do not want the filename hardcoded into the
//program!!




//The bit of code below works only if you use the
//char* filename. I have tried creating another variable
// and using strcpy and that does not work it keeps
//coming up with can not convert blah blah blah.

if((_access(fil ename,0))!=-1)
{
cout << filename << " Exists\n";
}
else
{
cout << filename << " Does Not Exist\n";
}
inData.open(fil ename);


I am new to c++ and it is more difficult than VB. If someone can help me
out with a solution that does what I want I would be very greatful.

My object is to:
1. Ask the user for the filename.
2. check for existance
3.If the file does not exist let the user create it or let
them use another data file.

I was thinking as an alternative checking for file existance using a system
call for a wildcard dat file and read them into an array and let the user
select the file or create a new one. But I thought the option above I am
trying to use would be more efficient and easier.

Thank You,
Shawn Mulligan
kazack@talon.ne t

[Jon Bell]

Re: File Input Error Help

In article <ZOinb.5980$Bv6 .1850150@news1. epix.net>,
kazack <kazack@talon.n et> wrote:

[snip]
[color=blue]
>void main()[/color]

Obligatory comp.lang.c++ admonishment: The C++ standard requires that
main return int, not void.

[snip]
[color=blue]
> char* filename;[/color]

This allocates memory for a pointer which is presumably intended to point
to the beginning of an array of characters. However, it does *not*
allocate memory for the characters themselves. This pointer is not
initialized to any particular value, and therefore points to some random
location in memory.

[snip]
[color=blue]
> cin >> filename;[/color]

Here you are entering a sequence of characters and trying to store them
beginning at the random memory location mentioned above, likely one which
you do not have privilege to access. Kaboom.

[snip]
[color=blue]
> inData.open(fil ename);[/color]

Since you are using #include <string>, you have available to you the
standard C++ string data type. Use it! Then you don't have to worry
about allocating memory to put the characters into; strings handle their
own memory allocation.

string filename;

cin >> filename;

inData.open (filename.c_str ());

You need the extra business in the open statment because it expects a
C-style "string"; c_str() gives you a pointer to a C-style string that
contains a copy of the contents of the real string.

--
Jon Bell <jtbellap8@pres by.edu> Presbyterian College
Dept. of Physics and Computer Science Clinton, South Carolina USA