Input and output streams maintain internal state information that indicates whether stream operations have completed successfully or whether an error has occurred. These state flags help a program detect conditions such as invalid input, reaching the end of a file, or unrecoverable stream errors.

The member functions good(), fail(), eof(), and bad() can be used to examine the current state of a stream after an input or output operation.

Source Code #

#include <iostream>

int main()
{
    int number;

    std::cout << "Enter an integer: ";
    std::cin >> number;

    std::cout << "good(): " << std::cin.good() << '\n';
    std::cout << "fail(): " << std::cin.fail() << '\n';
    std::cout << "eof(): " << std::cin.eof() << '\n';
    std::cout << "bad(): " << std::cin.bad() << '\n';

    return 0;
}

Output #

Enter an integer: 100
good(): 1
fail(): 0
eof(): 0
bad(): 0

Explanation #

• Input and output streams maintain internal state flags that describe the status of stream operations.
• good() returns true if no errors have occurred and the stream is ready for further operations.
• fail() returns true if an input or output operation has failed, such as attempting to read a non-numeric value into an integer.
• eof() returns true when the end of the input source has been reached.
• bad() returns true if a serious stream error has occurred, such as a loss of integrity in the stream buffer.
• These member functions return Boolean values, which are displayed as 1 for true and 0 for false by default.
• Checking stream state flags allows a program to detect and handle input and output errors safely.
• return 0; terminates the program successfully.