Thread: Passing a file pointer to a function is producing undesired output

Hello everyone,
I am working on a project and decided to try something simple before I start adding items. I am calling a function from main and that function has a file pointer. Here is my main.cpp

Code:

#include <cstdio>
#include <string>
#include <iostream>
#include "main.h"

extern FILE *fp;

using namespace std;

int main(int argc, char *argv[])
{
    
    char character;
    
    switch (argc)
    {
        case 1:
            fp = stdin;
            break;
            
        case 2:
            if ((fp = fopen((strcat(argv[1], ".cp")), "r")) == NULL)
            {
                cout << "Can't open input file!\n";
                exit (0);
            }
            break;
            
        default:
            cout << "USEAGE: testscanner <filename> OR testscanner\n";
            exit(0);
    }
    
    //while((character = getc(fp)) !=EOF)
    //{
        scanner(fp); 
    //}
    
    fclose(fp);
    
    return 1;
    
}

Here is the function:

Code:

#include <string>
#include <cstdio>
#include <iostream>
#include "main.h"
#include "scanner.h"

using namespace std;

void scanner(FILE *fp)
{
    char nextChar;

    while ((nextChar = getc(fp)) != EOF);
    {
        cout << nextChar << endl;       
    }

    fclose(fp);

}

My test file consists of several characters and digits. Nothing special and I at this point in time do not have any type of formatting that needs to be adhered to. I am simply wanting to read the file character by character and print it out. When I run the program, I get this symbol:

Code:

ÿ

If I use a printf statement, such as:

Code:

printf("%s\n", nextChar);

I get a segmentation fault. I know it has to be something really simple that I am missing and need another set of eyes.
My main.h

Code:

#ifndef MAIN_H
#define MAIN_H

void scanner(FILE *);
//char getChar(FILE *);

#endif

and lastly my scanner.h

Code:

#ifndef SCANNER_H
#define SCANNER_H

FILE *fp;

#endif

I hope someone can show me what I need to do in order to correct this. Thank you everyone.

Originally Posted by laserlight

Why are you using FILE instead of say, std::fstream?


nextChar is a char, not a null terminated string, yet you are trying to print it as a null terminated string.

Unless you have special requirements, make use of the C++-style I/O functionality instead. You already did so with:

Code:

cout << nextChar << endl;

Code:

printf("%c\n", nextChar);

Produces the same results.