C++ streambuf::sungetc() function

The C++ std::streambuf::sungetc() function is used to return the next character from the input sequence without advancing the current position of the stream buffer.

If no character is available, it returns EOF(end-of-file).

Syntax

Following is the syntax for std::streambuf::sungetc() function.

int_type sungetc();

Parameters

It does not accept any parameter.

Return Value

It returns the value of the new current character of the controlled input sequence, as a value of type int.

Exceptions

If an exception is thrown, the stream buffer is in a valid state.

Data races

It modifies the stream buffer object.

Example 1

In the following example, we are going to consider the basic usage of the sungetc() function.

#include <iostream>
#include <sstream>
int main() {
   std::istringstream a("Car");
   char b;
   b = a.get();
   a.rdbuf() -> sungetc();
   b = a.get();
   std::cout << "Result : " << b << std::endl;
   return 0;
}

Output

Output of the above code is as follows −

Result : C

Example 2

Consider the following example, where we are going to use the sungetc() function followed by the sgetc() function.

#include <iostream>
#include <sstream>
int main() {
   std::string x = "TP";
   std::stringbuf y(x);
   char x1 = y.sbumpc();
   std::cout << "Read character: " << x1 << std::endl;
   y.sungetc();
   char x2 = y.sgetc();
   std::cout << "After sungetc(), peeked character: " << x2 << std::endl;
   return 0;
}

Output

Following is the output of the above code −

Read character: T
After sungetc(), peeked character: T