NAME¶

std::basic_ios::fail - std::basic_ios::fail

Synopsis¶

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 <cstdlib>
#include <fstream>
#include <iostream>

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)