!file trickiness

mike7411

I have the following file code:

#include
#include
using namespace std;

int main() {

//add code below this line

string path = "student/text/readpractice.txt";

try {
    ifstream file;
    file.open(path); //content of file goes into memory buffer
    if (!file) {
        throw runtime\_error("File failed to open.");
    }
    cout << file.rdbuf(); //read the buffered content
    file.close();
}

catch (exception& e) {
    cerr << e.what() << endl;
}

//add code above this line

return 0;

}

Can someone help me understand how this line works:

if (!file) {

How can you use the exclamation point operator on what is probably a class? Is there some type of overloading that has occurred? I looked thru the code, and I couldn't find the ! point being overloaded. Any ideas? Thanks.

Maximilien

There is an operator! in ifstream [std::basic_ios<CharT,Traits>::operator! - cppreference.com](https://en.cppreference.com/w/cpp/io/basic\_ios/operator!) [https://stackoverflow.com/questions/59919741/what-is-the-difference-between-file-and-file-is-open\](https://stackoverflow.com/questions/59919741/what-is-the-difference-between-file-and-file-is-open)

CI/CD = Continuous Impediment/Continuous Despair

mike7411

Interesting. I tried doing a "Step Into" on that line in the debugger, but it won't go to it. If I do a "Go to Definition", it goes to this in xiosbase:

\_NODISCARD bool \_\_CLR\_OR\_THIS\_CALL operator!() const noexcept /\* strengthened \*/ {
    return fail();
}

However, I put a breakpoint there, and it doesn't break.

Lost User

mike7411 wrote:

Can someone help me understand how this line works:

the statement:

if (!file)

means if the variable file equals null then ... But you have already instantiated file with the line:

ifstream file;

So it is very unlikely that file will be null. The open method sets the failbit status if the open fails, and that is what you need to test. If you use STL classes then you must follow the STL rules, not the old C-style ones. See std::basic_ifstream<CharT,Traits>::open - cppreference.com[^] for full details.