That said, your program doesn't check whether it could successfully read the nominator and the denominator, separated by a slash.
That is, you normally compare the result of std::istream::peek() against the result of std::char_traits::to_int_type(), i.e., you'd use something like this: std::cin.peek() = std::char_traits::to_int_type('0') The result may, e.g., be std::char_traits::eof() and if the value of '0' happens to be negative (I'm not aware of any platform where it is however, e.g., the funny character from my name 'ü' is a negative value on platforms where char is signed) you wouldn't get the correct result, either. It is an error to seek before the beginning of the stream. Instead, it is an std::char_traits::int_type (which is a fancy spelling of int). IStream::Seek changes the seek pointer so that subsequent read and write operations can be performed at a different location in the stream object. These are the top rated real world C++ (Cpp) examples of std::istream::peek extracted from open source projects. peek() Returns the next character in the input stream and leaves it in the input stream as the starting point for the next read. The result from std::istream::peek() is not a char. C++ (Cpp) istream::peek - 30 examples found.You probably want to skip leading whitespace before determining what the next character is, e.g., using the manipulator std::ws: (std::cin > std::ws).peek(). This function access the next character and does not skip leading whitespace.If the operation sets an internal state flag that was registered with member exceptions, the function throws an exception of member type failure.There are two issues with your use of std::istream::peek(): Multiple flags may be set by a single operation. When set, the integrity of the stream may have been affected. The construction of sentry failed (such as when the stream state was not good before the call).Įrror on stream (such as when this function catches an exception thrown by an internal operation). No character could be peeked because the input sequence has no characters available (end-of-file reached). If there are no more characters to read in the input sequence, or if any internal state flags is set, the function returns the end-of-file value ( traits_type::eof()), and leaves the proper internal state flags set: Member type int_type is an integral type able to represent any character value or the special end-of-file value. The next character in the input sequence, converted to a value of type int_type using member traits_type::to_int_type. Then (if good), it reads one character from its associated stream buffer object by calling its member function sgetc, and finally destroys the sentry object before returning.Ĭalling this function sets the value returned by gcount to zero. Internally, the function accesses the input sequence by first constructing a sentry object (with noskipws set to true). peek ()' ') & ( istream>x )) Solution 2 Read the lines into a std::string using std::getline (), then assign the string to a std::istringstream object, and extract the data from that rather than directly from istream.
If any internal state flags is already set before the call or is set during the call, the function returns the end-of-file value ( traits_type::eof()). Solution 1 Use the peek method to check the next character: while ( ( istream. Returns the next character in the input sequence, without extracting it: The character is left as the next character to be extracted from the stream.
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