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123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130//// cgets.cpp//// Copyright (c) Microsoft Corporation. All rights reserved.//// Defines _cgets() and _cgets_s(), which read a string from the console.//#include <conio.h>#include <corecrt_internal_securecrt.h>#include <stdlib.h>
extern "C" { extern intptr_t __dcrt_lowio_console_input_handle; }
// Use of the following buffer variables is primarily for syncronizing with// _cgets_s. _cget_s fills the MBCS buffer and if the user passes in single// character buffer and the unicode character is not converted to single byte// MBC, then _cget_s should buffer that character so that next call to// _cgetws_s can return the same character.extern "C" { extern wchar_t __console_wchar_buffer; }extern "C" { extern int __console_wchar_buffer_used; }
// Reads a string from the console; always null-terminates the buffer. Returns// 0 on success; returns an errno error code on failure.extern "C" errno_t __cdecl _cgets_s(char* const source_string, size_t const size_in_bytes, size_t* const size_read){ _VALIDATE_CLEAR_OSSERR_RETURN_ERRCODE(source_string != nullptr, EINVAL); _VALIDATE_CLEAR_OSSERR_RETURN_ERRCODE(size_in_bytes > 0, EINVAL); _RESET_STRING(source_string, size_in_bytes);
_VALIDATE_CLEAR_OSSERR_RETURN_ERRCODE(size_read != nullptr, EINVAL);
errno_t error = 0; char* string = source_string;
__acrt_lock(__acrt_conio_lock); __try { // The implementation of cgets is slightly tricky. The reason being, // the code page for console is different from the CRT code page. // What this means is the program may interpret character // differently from it's acctual value. To fix this, what we really // want to do is read the input as unicode string and then convert // it to proper MBCS representation. // // This fix this we are really converting from Unicode to MBCS. // This adds performance problem as we may endup doing this // character by character. The basic problem here is that we have // no way to know how many UNICODE characters will be needed to fit // them in given size of MBCS buffer. To fix this issue we will be // converting one Unicode character at a time to MBCS. This makes // this slow, but then this is already console input, *size_read = 0;
size_t available = size_in_bytes - 1; do { wchar_t wchar_buff[2]; size_t sizeRead = 0;
error = _cgetws_s(wchar_buff, _countof(wchar_buff), &sizeRead); if (error != 0) break;
if (wchar_buff[0] == '\0') break;
int size_converted = 0; errno_t const wctomb_result = wctomb_s(&size_converted, string, available, wchar_buff[0]); if (wctomb_result != 0) { // Put the wide character back in the buffer so that the // unutilized wide character is still in the stream: __console_wchar_buffer = wchar_buff[0]; __console_wchar_buffer_used = 1; break; }
string += size_converted; *size_read += size_converted; available -= size_converted; } while (available > 0); } __finally { __acrt_unlock(__acrt_conio_lock); } __endtry
*string++ = '\0';
if (error != 0) errno = error;
return error;}
// Reads a string from the console via ReadConsole on a cooked console handle.// string[0] must contain the maximum length of the string. The number of// characters written is stored in string[1]. The return value is a pointer to// string[2] on success; nullptr on failure.extern "C" char* __cdecl _cgets(_Inout_z_ char* const string){ _VALIDATE_CLEAR_OSSERR_RETURN(string != nullptr, EINVAL, nullptr); _VALIDATE_CLEAR_OSSERR_RETURN(string[0] > 0, EINVAL, nullptr);
size_t const size_in_bytes = static_cast<size_t>(string[0]);
size_t size_read = 0; // warning 26018: Potential overflow of null terminated buffer using expression string+2 // Suppressing warning since _cgets is purposefully unsafe.#pragma warning(suppress:__WARNING_POTENTIAL_BUFFER_OVERFLOW_NULLTERMINATED) errno_t const result = _cgets_s(string + 2, size_in_bytes, &size_read);
// warning 26018: Potential overflow of null terminated buffer using expression string[1] // Suppressing warning since _cgets is purposefully unsafe.#pragma warning(suppress:__WARNING_POTENTIAL_BUFFER_OVERFLOW_NULLTERMINATED) string[1] = static_cast<char>(size_read);
return result == 0 ? string + 2 : nullptr;}