std::basic_ios<CharT,Traits>::fail

 

C++

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Technical Specifications

 

Input/output library

I/O manipulators

C-style I/O

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basic_streambuf

basic_filebuf

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ios_base

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basic_stringstream

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istrstream (deprecated in C++98)

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basic_osyncstream (C++20)

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streamoff

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iostream_category (C++11)

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std::basic_ios

Member functions

basic_ios::basic_ios

basic_ios::~basic_ios

State functions

basic_ios::good

basic_ios::eof

basic_ios::fail

basic_ios::bad

basic_ios::operator!

basic_ios::operator bool

basic_ios::rdstate

basic_ios::setstate

basic_ios::clear

Formatting

basic_ios::copyfmt

basic_ios::fill

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basic_ios::widen

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basic_ios::init

basic_ios::move

basic_ios::swap

basic_ios::set_rdbuf

 

bool fail() const;

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

See ios_base::iostate for the list of conditions that set failbit or badbit.

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

ferror

checks for a file error (function)