Retrieving all numbers from a certain text file - c++

Question

I have the following program:
#include <iostream>
#include <fstream>
#include <cstdlib>
using namespace std;
void tellen ()
{
ifstream input;
ofstream output;
char kar;
input.open ("test",ios::in);
kar = input.get();
while ( !input.eof() ){
if ( kar >= '0' and kar <= '9'){
cout << kar;
kar = input.get();
}
else
kar = input.get();
}
//cout << "Aantal characters:" << aantalchar << endl;
//cout << "Aantal regels:" << aantalregels << endl;
}
int main()
{
tellen();
return 0;
} //main
What I intended this program to do is to show me all numbers in a certain text file ("Test" in this case) in the command window. I'm wondering why this doesn't work? I have a file called test but when I run this the command prompt gives me a blank. The problem persists when I change "test" to "test.txt". Does anyone have a clue what the problem is? Maybe it has to do with the location of the file?

Answer 1

The following code will give you output of a txt file called test.
#include <iostream>
#include <fstream>
#include <cstdlib>
using namespace std;
void tellen() {
ifstream input;
ofstream output;
int kar;
char charKar;
input.open("test.txt", ios::in);
// could replace "test.txt" with a variable such as filePath = "/downloads/test.txt"
if (input.is_open()) {
while (!input.eof()) {
kar = input.get(); //kar gets inputed as an ASCII
charKar = static_cast<char>(kar);//charKar converts the ASCII into a char variable
if (charKar >= '0' && charKar <= '9'){ //Evaluate charKar, not kar
cout << charKar << endl;
}
}
input.close();
}
else {
cout << "\nFile Did Not Open!";
}
}
int main() {
tellen();
return 0;
} //main
I have tested the code and it works! Sorry if it's messy I was making eggs while coding this so if you have any questions just ask!

Answer 2

Things to change:
Add a check to make sure that the file was opened successfully.
Use type int when reading characters using istream::get() instead of char.
Change the while statement a bit.
void tellen (){
ifstream input;
ofstream output;
input.open ("test",ios::in);
if ( !input )
{
std::cerr << "Unable to open file.\n";
return;
}
int kar; // Don't use char.
while ( (kar = input.get()) != EOF ){
if ( kar >= '0' and kar <= '9'){
cout.put(kar); // I prefer this.
// cout << (char)kar;
}
}
//cout << "Aantal characters:" << aantalchar << endl;
//cout << "Aantal regels:" << aantalregels << endl;
}