asking user for output filename

[jojojlj]

I'm having some trouble with getting my program to display an error message when the user enters an incorrect filename. It just skips over the loop I put in for error displaying. Here's what my code looks like (trimmed down from what it is in my real program)

#include<fstream>
#include<iostream>

using namespace std;
int main(void){
string file_out;

ofstream fout;
cerr << "Please enter the name of a file for your output data > " << endl;
cin >> file_out;
cerr << "\n\n";
fout.open(file_out.c_str( ));

while( fout.fail( ) ) {
fout.clear( );
cerr << "The attempt to create your output file, " << file_out
<< ", failed. \n\n";
cerr << "Please enter the name of another output file. Make sure you "
<< "enter the FULL name \n" << "of the file > \n";
cin >> file_out;
cerr << "\n\n";
fout.open(file_out.c_str( ));
}

system("pause");

return 0;
}

I know people here say I shouldn't use system("pause"), but that's what our teacher always does and what he tells us to do. The program skips over the while loop if I enter an invalid file location and just finishes the program. I saw someone give the completed program as an answer here once, please don't do that for me.

[hamsterman]

If a file doesn't exist fstream creates it. I don't know how to make it only open existing files. You may have to find another library, or use os specific api.

[niross]

here is an example of opening files code:

#include <fstream>
int main() {
std::ofstream outputFile;
outputFile.open("out-file.txt");
if(!outputFile) {
std::cerr << “can’t open out-file.txt\n”;
std::exit(1);
}
outputFile << "here is an example of a text file..\n"
<< " the way we do it is similar to the way we send text \n"
<< " to the standard output stream" << std::endl;
}

[jojojlj]

@hamsterman: I can make it open existing files or create new ones if I enter a valid filename. The problem is that I want it to display an error message when I input a garbage filename like khlhbhgytd, and it doesn't do that.

@niross: I changed the while(fout.fail( )) to while(!fout) but that didn't make a difference to the way it compiled or ran, although it looks nicer. I write to the output file later in the program, which I didn't show. The rest of your code seems to be for when I'm typing the name of the file into the code, which isn't what my program is supposed to do. I have to ask the user for a filename and then open that file. Why do I need all the std::'s if I have #include<iostream>?

Am I doing the fout.open(file_out.c_str( )) correctly? Is that the problem line perhaps?

[jojojlj]

Problem solved! Turns out the "garbage" filenames I was inputting were interpreted as valid filenames; they were saved to the same region as the program was saved to but I didn't look there and so I didn't see them. When I inputted C:\ as a filename, then it gave me the error it was supposed to.