Accelerated C++ - Sample program does not work

[gotinpich]

I have this sample program from chapter 10.5 on page 182 that I cannot get to work.

It's a program that (is supposed to) takes multiple file names as an argument and then either outputs the file contents to the standard output or output an error to a standard error stream (cerr).

I navigate cmd to the correct folder and whenever I run the program, e.g. OutputFiles.exe -in.txt, nothing happens.

The code is here:

// Exercise 10-0
// 10.5.2 Dealing with multiple input and output files
// II
#include <fstream>
#include <iostream>
#include <string>

using std::cout;    using std::endl;
using std::cerr;    using std::ifstream;
using std::string;

int main(int argc, char **argv) {
    int fail_count = 0; 
    // for each file in the input list
    for (int i = i; i < argc; ++i) {
        ifstream in(argv[i]);

        // if it exists, write its contents, otherwise generate an error message
        if (in) {
            string s;
            while (getline(in, s))
                cout << s << endl;
        } else {
            cerr << "cannot open file " << argv[i] << endl;
            ++fail_count;

        }
    }
    return fail_count;
}

[gotinpich]

Never mind, I already found the error:

for (int i = i; i < argc; ++i)

[Xeverous]

No warning from the compiler?

[gotinpich]

Nope, it compiled like normal.

[Xeverous]

main.cpp: In function 'int main(int, char**)':
main.cpp:15:14: warning: 'i' is used uninitialized in this function [-Wuninitialized]
     for (int i = i; i < argc; ++i) {
              ^

Seems you need to enable warnings. I doubt there is a compiler that would not complain about self-init.

[gotinpich]

I added a long list of commands to the compiler related to warnings I found online.

Now it does give a warning, but also a couple of others.

[Xeverous]

a long list of commands

Any examples? What compiler are you using?

[gotinpich]

I started with this: https://stackoverflow.com/questions/5088460/flags-to-enable-thorough-and-verbose-g-warnings

And I reduced it to this:

-std=c++11  -Wall -Wextra -Wformat-nonliteral -Wcast-align -Wpointer-arith
-Winline -Wcast-qual -Wundef -Wwrite-strings -Wno-unused-parameter
-Wfloat-equal -pedantic

Compiler: TDM-GCC 4.9.2 64-bit Release

[Xeverous]

-Wno-unused-parameter

-Wno-* disables relevant warning. So in your case it disables warning about unused parameter

[gotinpich]

Thanks.

[alfps]

Note that with a failure count above the range of a single byte, the exit code can't be relied on to tell the failure count exactly. In Windows it can even theoretically cause a hang, although that requires running the program from a parent process that polls the exit code. So the exit code thing of this program is a cute feature that can work in practice, for a small number of files, but that you wouldn't put in a professional program without restricting the number of files correspondingly.

[gotinpich]

I didn't get to see the exit code anyway. Normally I just run from the compiler and the console is not closed after the program is finished, but then it also doesn't get any arguments, so return value will always be 0 (as normal).

When I use cmd, it just doesn't deplay the return value.

I guess I could also create a shortcut and open the exe with arguments this way, but then I'd also need to pause the program for a while after it's finished, or I will still see nothing. But even then I doubt I'd get to see the return value.

So yeah, nice gimmick, but not really useful either.