C++ IOS::rdstate() function

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The C++ std::ios::rdstate() function is used to manage the state of input/output streams. It returns the state of the stream as a bitmask, indicating various errors and state flags. These flags indicates the various errors, such as failbit(logical operation failed), badbit(error occured), eofbit(end of file reached).

Syntax

Following is the syntax for std::ios::rdstate() function.

iostate rdstate() const;

Parameters

It does not accepts any parameter.

Return Value

An object of type ios_base::iostate that can contain any combination of the following state flag member constants −

iostate value (member constant)	indicates	functions to check state flags
		good()	eof()	fail()	bad()	rdstate()
goodbit	No errors (zero value iostate)	true	false	false	false	goodbit
eofbit	End-of-File reached on input operation	false	true	false	false	eofbit
failbit	Logical error on i/o operation	false	false	true	false	failbit
badbit	Read/writing error on i/o operation	false	false	true	true	badbit

Exceptions

If an exception is thrown, there are no changes in the stream.

Data Races

Accesses the stream object.

Concurrent access to the same stream object may cause data races.

Example

Let's look at the following example, where we are going to check the stream state after an input operation.

#include <iostream>
#include <sstream>
int main()
{
    std::stringstream a("112 TP");
    int x;
    a >> x;
    if (a.rdstate() & std::ios::failbit) {
        std::cout << "Stream Reading Failed.\n";
    } else {
        std::cout << "Stream Read Successfully.\n";
    }
    return 0;
}

Output

Output of the above code is as follows −

Stream Read Successfully.

Example

Consider the following example, where we are going to check stream state after a failed input operation.

#include <iostream>
#include <sstream>
int main()
{
    std::stringstream ss("TutorialsPoint");
    int number;
    ss >> number;
    if (ss.rdstate() & std::ios::failbit) {
        std::cout << "Stream Failed To Read.\n";
    } else {
        std::cout << "Stream Read successfully.\n";
    }
    return 0;
}

Output

Following is the output of the above code −

Stream Failed To Read.

Example

In the following example, we are going to check stream state after end-of-file (EOF) operation.

#include <iostream>
#include <sstream>
int main()
{
    std::stringstream a("WELCOME");
    std::string b;
    std::getline(a, b);
    if (a.rdstate() & std::ios::eofbit) {
        std::cout << "End Of File Reached.\n";
    } else {
        std::cout << "File Not At End.\n";
    }
    return 0;
}

Output

If we run the above code it will generate the following output −

End Of File Reached.