# std::basic_ios::operator!

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< cpp‎ | io‎ | basic ios

bool operator!() const; |  |

Returns true if an error has occurred on the associated stream. Specifically, returns true if `badbit` or `failbit` is set in rdstate().

### Parameters

(none)

### Return value

true if an error has occurred, false otherwise.

### Example

Run this code

    #include <iostream>
    #include <fstream>
    #include <cstdlib>
    int main()
    {
        std::ifstream file("test.txt");
        if(!file)  // operator! is used here
        {
            std::cout << "File opening failed\n";
            return EXIT_FAILURE;
        }

        // typical C++ I/O loop uses the return value of the I/O function
        // as the loop controlling condition, operator bool() is used here
        for(int n; file >> n; ) {
           std::cout << n << ' ';
        }
        std::cout << '\n';

        if (file.bad())
            std::cout << "I/O error while reading\n";
        else if (file.eof())
            std::cout << "End of file reached successfully\n";
        else if (file.fail())
            std::cout << "Non-integer data encountered\n";
    }

### See also

The following table shows the value of `basic_ios` accessors (`good()`, `fail()`, etc.) for all possible combinations of `ios_base::iostate` flags:

`ios_base::iostate` flags | `basic_ios` accessors
eofbit | failbit | badbit | `good()` | `fail()` | `bad()` | `eof()` | `operator bool` | `operator!`
false | false | false | true | false | false | false | true | false
false | false | true | false | true | true | false | false | true
false | true | false | false | true | false | false | false | true
false | true | true | false | true | true | false | false | true
true | false | false | false | false | false | true | true | false
true | false | true | false | true | true | true | false | true
true | true | false | false | true | false | true | false | true
true | true | true | false | true | true | true | false | true

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