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Reactos
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12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596061626364656667686970717273747576777879808182838485868788899091929394//// ungetc.cpp//// Copyright (c) Microsoft Corporation. All rights reserved.//// Defines ungetc(), which pushes a character back into a stream.//#include <corecrt_internal_stdio.h>
// Pushes a character ("ungets" it) back into a stream. It is possible to push// back one character. It may not be possible to push back more than one// character in a row. Returns the pushed-back character on success; returns// EOF on failure. Ungetting EOF is expressly forbidden.extern "C" int __cdecl ungetc(int const c, FILE* const stream){ _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;}
extern "C" int __cdecl _ungetc_nolock(int const c, FILE* public_stream){ __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;}