How to read the whole istream correctly?

Question

Here is a simple code to print all characters of a txt file on screen:

#include <iostream>
#include <fstream>
#include <string>
using namespace std;

int main() {
       int **i;
       int j,k;
       char a;
    ifstream test("test.txt", ios::binary);
    while((a=test.get())!=-1)//if I use "while(!test.eof())" here, how to avoid the output of the last character(-1) to std::cout, or any ostream objects?
    {
   putchar(a);//also change this to putchar(test.get());
    }
       getchar();
}

As I noted in the code, if I use "test.eof()" to judge the end of test.txt, I'll always get an extra blank at the end of the output. How to avoid it?

Answer 1

You want:

int a;

The get() function returns an int, not a char - this is the same in C - when using getchar(), you read into an int variable not char. So your loop looks like:

while( ( a = test.get() ) != EOF )

note you want EOF here, not eof(). a version using eof() would look like this:

char c;
while( test.get( c ) ) {
   putchar( c );   // or whatever
}

if ( test.eof() ) {
  // Ok, we finished because of end of file
}
else {
  // finished not because of end of file - probably an error
}

Answer 2

the get method will only set the eof error bit after an attempt to read past the EOF. That's why you get the extra blank with the while (!test.eof()) case. Generally you always have to read past the EOF before detecting that an EOF occurred. Maybe you could do it like this:

char c = test.get();
while (!test.eof()) {
    putchar(c);
    c = test.get();
}

or rewritten as for:

for (char c = test.get(); !test.eof(); c = test.get()) {
    putchar(c);
}