ungetc.cpp File Reference

#include <corecrt_internal_stdio.h>

Include dependency graph for ungetc.cpp:

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Functions
int __cdecl	ungetc (int const c, FILE *const stream)
int __cdecl	_ungetc_nolock (int const c, FILE *public_stream)

Function Documentation

_ungetc_nolock()

int __cdecl _ungetc_nolock	(	int const	c,
		FILE *	public_stream
	)

Definition at line 38 of file ungetc.cpp.

{
    __crt_stdio_stream const stream(public_stream);
 
    _VALIDATE_STREAM_ANSI_RETURN(stream, EINVAL, EOF);
 
    // Ungetting EOF is expressly forbidden:
    if (c == EOF)
        return EOF;
 
    // The stream must either be open in read-only mode, or must be open in
    // read-write mode and must not currently be in write mode:
    bool const is_in_read_only_mode = stream.has_all_of(_IOREAD);
    bool const is_in_rw_write_mode =  stream.has_all_of(_IOUPDATE | _IOWRITE);
 
    if (!is_in_read_only_mode && !is_in_rw_write_mode)
        return EOF;
 
    // If the stream is currently unbuffered, buffer it:
    if (stream->_base == nullptr)
        __acrt_stdio_allocate_buffer_nolock(stream.public_stream());
 
    // At this point, we know that _base is not null, since the file is buffered.
 
    if (stream->_ptr == stream->_base)
    {
        // If we've already buffered a pushed-back character, there's no room for
        // another, and there's nothing we can do:
        if (stream->_cnt)
            return EOF;
 
        ++stream->_ptr;
    }
 
    // If the stream is string-backed (and not file-backed), do not modify the buffer:
    if (stream.is_string_backed())
    {
        --stream->_ptr;
        if (*stream->_ptr != static_cast<char>(c))
        {
            ++stream->_ptr;
            return EOF;
        }
    }
    else
    {
        --stream->_ptr;
        *stream->_ptr = static_cast<char>(c);
    }
 
    ++stream->_cnt;
    stream.unset_flags(_IOEOF);
    stream.set_flags(_IOREAD);
 
    return c & 0xff;
}

Referenced by ungetc().

ungetc()

int __cdecl ungetc	(	int const	c,
		FILE *const	stream
	)

Definition at line 16 of file ungetc.cpp.

{
    _VALIDATE_RETURN(stream != nullptr, EINVAL, EOF);
 
    int return_value = EOF;
 
    _lock_file(stream);
    __try
    {
        return_value = _ungetc_nolock(c, stream);
    }
    __finally
    {
        _unlock_file(stream);
    }
    __endtry
 
    return return_value;
}