Existe um substituto para unistd.h para Windows (Visual C)?

Estou portando um programa de console relativamente simples escrito para Unix na plataforma Windows ( Visual C ++ 8.0 ). Todos os arquivos de origem incluem "unistd.h", que não existe. Ao removê-lo, recebo reclamações sobre a falta de protótipos para 'srandom', 'random' e 'getopt'. Eu sei que posso substituir as funções aleatórias e tenho certeza de que posso encontrar / hackear uma implementação getopt.

Mas tenho certeza que outros enfrentaram o mesmo desafio. Minha pergunta é: existe uma porta de "unistd.h" para o Windows? Pelo menos um contendo as funções que possuem uma implementação nativa do Windows - não preciso de canos ou bifurcações.

EDIT :

Eu sei que posso criar meu próprio "unistd.h", que contém substituições para as coisas que eu preciso - especialmente neste caso, pois é um conjunto limitado. Mas, como parece um problema comum, eu queria saber se alguém já havia feito o trabalho para um subconjunto maior da funcionalidade.

Mudar para um compilador ou ambiente diferente não é possível no trabalho - estou preso ao Visual Studio.

Como não conseguimos encontrar uma versão na Internet, vamos começar uma aqui.
A maioria das portas para o Windows provavelmente só precisa de um subconjunto do arquivo Unix completo.
Aqui está um ponto de partida. Adicione definições conforme necessário.

#ifndef _UNISTD_H
#define _UNISTD_H    1

/* This is intended as a drop-in replacement for unistd.h on Windows.
 * Please add functionality as neeeded.
 * https://stackoverflow.com/a/826027/1202830
 */

#include <stdlib.h>
#include <io.h>
#include <getopt.h> /* getopt at: https://gist.github.com/ashelly/7776712 */
#include <process.h> /* for getpid() and the exec..() family */
#include <direct.h> /* for _getcwd() and _chdir() */

#define srandom srand
#define random rand

/* Values for the second argument to access.
   These may be OR'd together.  */
#define R_OK    4       /* Test for read permission.  */
#define W_OK    2       /* Test for write permission.  */
//#define   X_OK    1       /* execute permission - unsupported in windows*/
#define F_OK    0       /* Test for existence.  */

#define access _access
#define dup2 _dup2
#define execve _execve
#define ftruncate _chsize
#define unlink _unlink
#define fileno _fileno
#define getcwd _getcwd
#define chdir _chdir
#define isatty _isatty
#define lseek _lseek
/* read, write, and close are NOT being #defined here, because while there are file handle specific versions for Windows, they probably don't work for sockets. You need to look at your app and consider whether to call e.g. closesocket(). */

#ifdef _WIN64
#define ssize_t __int64
#else
#define ssize_t long
#endif

#define STDIN_FILENO 0
#define STDOUT_FILENO 1
#define STDERR_FILENO 2
/* should be in some equivalent to <sys/types.h> */
typedef __int8            int8_t;
typedef __int16           int16_t; 
typedef __int32           int32_t;
typedef __int64           int64_t;
typedef unsigned __int8   uint8_t;
typedef unsigned __int16  uint16_t;
typedef unsigned __int32  uint32_t;
typedef unsigned __int64  uint64_t;

#endif /* unistd.h  */

Tente incluir o io.harquivo. Parece ser o equivalente do Visual Studio unistd.h.

Eu espero que isso ajude.

Eu recomendaria usar mingw / msys como um ambiente de desenvolvimento. Especialmente se você estiver portando programas simples de console. O Msys implementa um shell semelhante ao Unix no Windows, e o mingw é uma porta da coleção de compiladores GNU (GCC) e outras ferramentas de criação do GNU para a plataforma Windows. É um projeto de código aberto e adequado para a tarefa. Atualmente, eu o uso para criar programas utilitários e aplicativos de console para o Windows XP, e certamente tem esse unistd.hcabeçalho que você está procurando.

O procedimento de instalação pode ser um pouco complicado, mas eu achei que o melhor lugar para começar é no MSYS .

Eu tropecei nessa discussão enquanto tentava encontrar uma alternativa para o Windows getpid()(definida em unistd.h). Acontece que incluir process.hfaz o truque. Talvez isso ajude as pessoas que encontrarem esse tópico no futuro.

Não, no IIRC não há getopt () no Windows.

O Boost , no entanto, possui a biblioteca program_options ... que funciona bem. A princípio, parecerá um exagero, mas não é terrível, especialmente considerando que ele pode lidar com a configuração de opções de programa em arquivos de configuração e variáveis ​​de ambiente, além das opções da linha de comando.

MinGW 4.x tem em unistd.h \MinGW\include, \MinGW\include\syse \MinGW\lib\gcc\mingw32\4.6.2\include\ssp

Aqui está o código para a versão MinGW, de Rob Savoye; modificado por Earnie Boyd, Danny Smith, Ramiro Polla, Gregory McGarry e Keith Marshall:

/*
 * unistd.h
 *
 * Standard header file declaring MinGW's POSIX compatibility features.
 *
 * $Id: unistd.h,v c3ebd36f8211 2016/02/16 16:05:39 keithmarshall $
 *
 * Written by Rob Savoye <[email protected]>
 * Modified by Earnie Boyd <[email protected]>
 *   Danny Smith <[email protected]>
 *   Ramiro Polla <[email protected]>
 *   Gregory McGarry  <[email protected]>
 *   Keith Marshall  <[email protected]>
 * Copyright (C) 1997, 1999, 2002-2004, 2007-2009, 2014-2016,
 *   MinGW.org Project.
 *
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice, this permission notice, and the following
 * disclaimer shall be included in all copies or substantial portions of
 * the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OF OR OTHER
 * DEALINGS IN THE SOFTWARE.
 *
 */
#ifndef _UNISTD_H
#define _UNISTD_H  1
#pragma GCC system_header

/* All MinGW headers MUST include _mingw.h before anything else,
 * to ensure proper initialization of feature test macros.
 */
#include <_mingw.h>

/* unistd.h maps (roughly) to Microsoft's <io.h>
 * Other headers included by <unistd.h> may be selectively processed;
 * __UNISTD_H_SOURCED__ enables such selective processing.
 */
#define __UNISTD_H_SOURCED__ 1

#include <io.h>
#include <process.h>
#include <getopt.h>

/* These are defined in stdio.h.  POSIX also requires that they
 * are to be consistently defined here; don't guard against prior
 * definitions, as this might conceal inconsistencies.
 */
#define SEEK_SET   0
#define SEEK_CUR   1
#define SEEK_END   2

#if _POSIX_C_SOURCE
/* POSIX process/thread suspension functions; all are supported by a
 * common MinGW API in libmingwex.a, providing for suspension periods
 * ranging from mean values of ~7.5 milliseconds, (see the comments in
 * <time.h>), extending up to a maximum of ~136 years.
 *
 * Note that, whereas POSIX supports early wake-up of any suspended
 * process/thread, in response to a signal, this implementation makes
 * no attempt to emulate this signalling behaviour, (since signals are
 * not well supported by Windows); thus, unless impeded by an invalid
 * argument, this implementation always returns an indication as if
 * the sleeping period ran to completion.
 */
_BEGIN_C_DECLS

__cdecl __MINGW_NOTHROW
int __mingw_sleep( unsigned long, unsigned long );

/* The nanosleep() function provides the most general purpose API for
 * process/thread suspension; it is declared in <time.h>, (where it is
 * accompanied by an in-line implementation), rather than here, and it
 * provides for specification of suspension periods in the range from
 * ~7.5 ms mean, (on WinNT derivatives; ~27.5 ms on Win9x), extending
 * up to ~136 years, (effectively eternity).
 *
 * The usleep() function, and its associated useconds_t type specifier
 * were made obsolete in POSIX.1-2008; declared here, only for backward
 * compatibility, its continued use is not recommended.  (It is limited
 * to specification of suspension periods ranging from ~7.5 ms mean up
 * to a maximum of 999,999 microseconds only).
 */
typedef unsigned long useconds_t __MINGW_ATTRIB_DEPRECATED;
int __cdecl __MINGW_NOTHROW usleep( useconds_t )__MINGW_ATTRIB_DEPRECATED;

#ifndef __NO_INLINE__
__CRT_INLINE __LIBIMPL__(( FUNCTION = usleep ))
int usleep( useconds_t period ){ return __mingw_sleep( 0, 1000 * period ); }
#endif

/* The sleep() function is, perhaps, the most commonly used of all the
 * process/thread suspension APIs; it provides support for specification
 * of suspension periods ranging from 1 second to ~136 years.  (However,
 * POSIX recommends limiting the maximum period to 65535 seconds, to
 * maintain portability to platforms with only 16-bit ints).
 */
unsigned __cdecl __MINGW_NOTHROW sleep( unsigned );

#ifndef __NO_INLINE__
__CRT_INLINE __LIBIMPL__(( FUNCTION = sleep ))
unsigned sleep( unsigned period ){ return __mingw_sleep( period, 0 ); }
#endif


/* POSIX ftruncate() function.
 *
 * Microsoft's _chsize() function is incorrectly described, on MSDN,
 * as a preferred replacement for the POSIX chsize() function.  There
 * never was any such POSIX function; the actual POSIX equivalent is
 * the ftruncate() function.
 */
int __cdecl ftruncate( int, off_t );

#ifndef __NO_INLINE__
__CRT_INLINE __JMPSTUB__(( FUNCTION = ftruncate, REMAPPED = _chsize ))
int ftruncate( int __fd, off_t __length ){ return _chsize( __fd, __length ); }
#endif

_END_C_DECLS

#endif /* _POSIX_C_SOURCE */

#undef __UNISTD_H_SOURCED__
#endif /* ! _UNISTD_H: $RCSfile: unistd.h,v $: end of file */

Este arquivo requer a inclusão de _mingw.h, que é o seguinte:

#ifndef __MINGW_H
/*
 * _mingw.h
 *
 * MinGW specific macros included by ALL mingwrt include files; (this file
 * is part of the MinGW32 runtime library package).
 *
 * $Id: _mingw.h.in,v 7daa0459f602 2016/05/03 17:40:54 keithmarshall $
 *
 * Written by Mumit Khan  <[email protected]>
 * Copyright (C) 1999, 2001-2011, 2014-2016, MinGW.org Project
 *
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 *
 */
#define __MINGW_H

/* In previous versions, __MINGW32_VERSION was expressed as a dotted
 * numeric pair, representing major.minor; unfortunately, this doesn't
 * adapt well to the inclusion of a patch-level component, since the
 * major.minor.patch dotted triplet representation is not valid as a
 * numeric entity.  Thus, for this version, we adopt a representation
 * which encodes the version as a long integer value, expressing:
 *
 *   __MINGW32_VERSION = 1,000,000 * major + 1,000 * minor + patch
 *
 * DO NOT EDIT these package version assignments manually; they are
 * derived from the package version specification within configure.ac,
 * whence they are propagated automatically, at package build time.
 */
#define __MINGW32_VERSION           3022001L
#define __MINGW32_MAJOR_VERSION           3
#define __MINGW32_MINOR_VERSION          22
#define __MINGW32_PATCHLEVEL              1

#if __GNUC__ >= 3 && ! defined __PCC__
#pragma GCC system_header
#endif

#ifndef _MSVCRTVER_H
/* Legacy versions of mingwrt use the macro __MSVCRT_VERSION__ to
 * enable evolving features of different MSVCRT.DLL versions.  This
 * usage is no longer recommended, but the __MSVCRT_VERSION__ macro
 * remains useful when a non-freely distributable MSVCRxx.DLL is to
 * be substituted for MSVCRT.DLL; for such usage, the substitute
 * MSVCRxx.DLL may be identified as specified in...
 */
# include <msvcrtver.h>
#endif

/* A better inference than __MSVCRT_VERSION__, of the capabilities
 * supported by the operating system default MSVCRT.DLL, is provided
 * by the Windows API version identification macros.
 */
#include <w32api.h>

/* The following are defined by the user (or by the compiler), to specify how
 * identifiers are imported from a DLL.  All headers should include this first,
 * and then use __DECLSPEC_SUPPORTED to choose between the old ``__imp__name''
 * style or the __MINGW_IMPORT style for declarations.
 *
 * __DECLSPEC_SUPPORTED            Defined if dllimport attribute is supported.
 * __MINGW_IMPORT                  The attribute definition to specify imported
 *                                 variables/functions.
 * _CRTIMP                         As above.  For MS compatibility.
 *
 * Macros to enable MinGW features which deviate from standard MSVC
 * compatible behaviour; these may be specified directly in user code,
 * activated implicitly, (e.g. by specifying _POSIX_C_SOURCE or such),
 * or by inclusion in __MINGW_FEATURES__:
 *
 * __USE_MINGW_ANSI_STDIO          Select a more ANSI C99 compatible
 *                                 implementation of printf() and friends;
 *                                 (users should not set this directly).
 *
 * Other macros:
 *
 * __int64                         define to be long long.  Using a typedef
 *                                 doesn't work for "unsigned __int64"
 *
 *
 * Manifest definitions for flags to control globbing of the command line
 * during application start up, (before main() is called).  The first pair,
 * when assigned as bit flags within _CRT_glob, select the globbing algorithm
 * to be used; (the MINGW algorithm overrides MSCVRT, if both are specified).
 * Prior to mingwrt-3.21, only the MSVCRT option was supported; this choice
 * may produce different results, depending on which particular version of
 * MSVCRT.DLL is in use; (in recent versions, it seems to have become
 * definitively broken, when globbing within double quotes).
 */
#define __CRT_GLOB_USE_MSVCRT__     0x0001

/* From mingwrt-3.21 onward, this should be the preferred choice; it will
 * produce consistent results, regardless of the MSVCRT.DLL version in use.
 */
#define __CRT_GLOB_USE_MINGW__      0x0002

/* When the __CRT_GLOB_USE_MINGW__ flag is set, within _CRT_glob, the
 * following additional options are also available; they are not enabled
 * by default, but the user may elect to enable any combination of them,
 * by setting _CRT_glob to the boolean sum (i.e. logical OR combination)
 * of __CRT_GLOB_USE_MINGW__ and the desired options.
 *
 *    __CRT_GLOB_USE_SINGLE_QUOTE__ allows use of single (apostrophe)
 *                      quoting characters, analogously to
 *                      POSIX usage, as an alternative to
 *                      double quotes, for collection of
 *                      arguments separated by white space
 *                      into a single logical argument.
 *
 *    __CRT_GLOB_BRACKET_GROUPS__   enable interpretation of bracketed
 *                      character groups as POSIX compatible
 *                      globbing patterns, matching any one
 *                      character which is either included
 *                      in, or excluded from the group.
 *
 *    __CRT_GLOB_CASE_SENSITIVE__   enable case sensitive matching for
 *                      globbing patterns; this is default
 *                      behaviour for POSIX, but because of
 *                      the case insensitive nature of the
 *                      MS-Windows file system, it is more
 *                      appropriate to use case insensitive
 *                      globbing as the MinGW default.
 *
 */
#define __CRT_GLOB_USE_SINGLE_QUOTE__   0x0010
#define __CRT_GLOB_BRACKET_GROUPS__ 0x0020
#define __CRT_GLOB_CASE_SENSITIVE__ 0x0040

/* The MinGW globbing algorithm uses the ASCII DEL control code as a marker
 * for globbing characters which were embedded within quoted arguments; (the
 * quotes are stripped away BEFORE the argument is globbed; the globbing code
 * treats the marked character as immutable, and strips out the DEL markers,
 * before storing the resultant argument).  The DEL code is mapped to this
 * function here; DO NOT change it, without rebuilding the runtime.
 */
#define __CRT_GLOB_ESCAPE_CHAR__    (char)(127)


/* Manifest definitions identifying the flag bits, controlling activation
 * of MinGW features, as specified by the user in __MINGW_FEATURES__.
 */
#define __MINGW_ANSI_STDIO__        0x0000000000000001ULL
/*
 * The following three are not yet formally supported; they are
 * included here, to document anticipated future usage.
 */
#define __MINGW_LC_EXTENSIONS__     0x0000000000000050ULL
#define __MINGW_LC_MESSAGES__       0x0000000000000010ULL
#define __MINGW_LC_ENVVARS__        0x0000000000000040ULL


/* Try to avoid problems with outdated checks for GCC __attribute__ support.
 */
#undef __attribute__

#if defined (__PCC__)
#  undef __DECLSPEC_SUPPORTED
# ifndef __MINGW_IMPORT
#  define __MINGW_IMPORT extern
# endif
# ifndef _CRTIMP
#  define _CRTIMP
# endif
# ifndef __cdecl
#  define __cdecl  _Pragma("cdecl")
# endif
# ifndef __stdcall
#  define __stdcall _Pragma("stdcall")
# endif
# ifndef __int64
#  define __int64 long long
# endif
# ifndef __int32
#  define __int32 long
# endif
# ifndef __int16
#  define __int16 short
# endif
# ifndef __int8
#  define __int8 char
# endif
# ifndef __small
#  define __small char
# endif
# ifndef __hyper
#  define __hyper long long
# endif
# ifndef __volatile__
#  define __volatile__ volatile
# endif
# ifndef __restrict__
#  define __restrict__ restrict
# endif
# define NONAMELESSUNION
#elif defined(__GNUC__)
# ifdef __declspec
#  ifndef __MINGW_IMPORT
   /* Note the extern. This is needed to work around GCC's
      limitations in handling dllimport attribute.  */
#   define __MINGW_IMPORT  extern __attribute__((__dllimport__))
#  endif
#  ifndef _CRTIMP
#   ifdef __USE_CRTIMP
#    define _CRTIMP  __attribute__((dllimport))
#   else
#    define _CRTIMP
#   endif
#  endif
#  define __DECLSPEC_SUPPORTED
# else /* __declspec */
#  undef __DECLSPEC_SUPPORTED
#  undef __MINGW_IMPORT
#  ifndef _CRTIMP
#   define _CRTIMP
#  endif
# endif /* __declspec */
/*
 * The next two defines can cause problems if user code adds the
 * __cdecl attribute like so:
 * void __attribute__ ((__cdecl)) foo(void);
 */
# ifndef __cdecl
#  define __cdecl  __attribute__((__cdecl__))
# endif
# ifndef __stdcall
#  define __stdcall __attribute__((__stdcall__))
# endif
# ifndef __int64
#  define __int64 long long
# endif
# ifndef __int32
#  define __int32 long
# endif
# ifndef __int16
#  define __int16 short
# endif
# ifndef __int8
#  define __int8 char
# endif
# ifndef __small
#  define __small char
# endif
# ifndef __hyper
#  define __hyper long long
# endif
#else /* ! __GNUC__ && ! __PCC__ */
# ifndef __MINGW_IMPORT
#  define __MINGW_IMPORT  __declspec(dllimport)
# endif
# ifndef _CRTIMP
#  define _CRTIMP  __declspec(dllimport)
# endif
# define __DECLSPEC_SUPPORTED
# define __attribute__(x) /* nothing */
#endif

#if defined (__GNUC__) && defined (__GNUC_MINOR__)
#define __MINGW_GNUC_PREREQ(major, minor) \
  (__GNUC__ > (major) \
   || (__GNUC__ == (major) && __GNUC_MINOR__ >= (minor)))
#else
#define __MINGW_GNUC_PREREQ(major, minor)  0
#endif

#ifdef __cplusplus
# define __CRT_INLINE    inline
#else
# if __GNUC_STDC_INLINE__
#  define __CRT_INLINE   extern inline __attribute__((__gnu_inline__))
# else
#  define __CRT_INLINE   extern __inline__
# endif
#endif

# ifdef __GNUC__
  /* A special form of __CRT_INLINE is provided; it will ALWAYS request
   * inlining when possible.  Originally specified as _CRTALIAS, this is
   * now deprecated in favour of __CRT_ALIAS, for syntactic consistency
   * with __CRT_INLINE itself.
   */
#  define  _CRTALIAS   __CRT_INLINE __attribute__((__always_inline__))
#  define __CRT_ALIAS  __CRT_INLINE __attribute__((__always_inline__))
# else
#  define  _CRTALIAS   __CRT_INLINE /* deprecated form */
#  define __CRT_ALIAS  __CRT_INLINE /* preferred form */
# endif
/*
 * Each function which is implemented as a __CRT_ALIAS should also be
 * accompanied by an externally visible interface.  The following pair
 * of macros provide a mechanism for implementing this, either as a stub
 * redirecting to an alternative external function, or by compilation of
 * the normally inlined code into free standing object code; each macro
 * provides a way for us to offer arbitrary hints for use by the build
 * system, while remaining transparent to the compiler.
 */
#define __JMPSTUB__(__BUILD_HINT__)
#define __LIBIMPL__(__BUILD_HINT__)

#ifdef __cplusplus
# define __UNUSED_PARAM(x)
#else
# ifdef __GNUC__
#  define __UNUSED_PARAM(x) x __attribute__((__unused__))
# else
#  define __UNUSED_PARAM(x) x
# endif
#endif

#ifdef __GNUC__
#define __MINGW_ATTRIB_NORETURN __attribute__((__noreturn__))
#define __MINGW_ATTRIB_CONST __attribute__((__const__))
#else
#define __MINGW_ATTRIB_NORETURN
#define __MINGW_ATTRIB_CONST
#endif

#if __MINGW_GNUC_PREREQ (3, 0)
#define __MINGW_ATTRIB_MALLOC __attribute__((__malloc__))
#define __MINGW_ATTRIB_PURE __attribute__((__pure__))
#else
#define __MINGW_ATTRIB_MALLOC
#define __MINGW_ATTRIB_PURE
#endif

/* Attribute `nonnull' was valid as of gcc 3.3.  We don't use GCC's
   variadiac macro facility, because variadic macros cause syntax
   errors with  --traditional-cpp.  */
#if  __MINGW_GNUC_PREREQ (3, 3)
#define __MINGW_ATTRIB_NONNULL(arg) __attribute__((__nonnull__(arg)))
#else
#define __MINGW_ATTRIB_NONNULL(arg)
#endif /* GNUC >= 3.3 */

#if  __MINGW_GNUC_PREREQ (3, 1)
#define __MINGW_ATTRIB_DEPRECATED __attribute__((__deprecated__))
#else
#define __MINGW_ATTRIB_DEPRECATED
#endif /* GNUC >= 3.1 */

#if  __MINGW_GNUC_PREREQ (3, 3)
#define __MINGW_NOTHROW __attribute__((__nothrow__))
#else
#define __MINGW_NOTHROW
#endif /* GNUC >= 3.3 */


/* TODO: Mark (almost) all CRT functions as __MINGW_NOTHROW.  This will
allow GCC to optimize away some EH unwind code, at least in DW2 case.  */

/* Activation of MinGW specific extended features:
 */
#ifndef __USE_MINGW_ANSI_STDIO
/* Users should not set this directly; rather, define one (or more)
 * of the feature test macros (tabulated below), or specify any of the
 * compiler's command line options, (e.g. -posix, -ansi, or -std=c...),
 * which cause _POSIX_SOURCE, or __STRICT_ANSI__ to be defined.
 *
 * We must check this BEFORE we specifiy any implicit _POSIX_C_SOURCE,
 * otherwise we would always implicitly choose __USE_MINGW_ANSI_STDIO,
 * even if none of these selectors are specified explicitly...
 */
# if   defined __STRICT_ANSI__  ||  defined _ISOC99_SOURCE \
   ||  defined _POSIX_SOURCE    ||  defined _POSIX_C_SOURCE \
   ||  defined _XOPEN_SOURCE    ||  defined _XOPEN_SOURCE_EXTENDED \
   ||  defined _GNU_SOURCE      ||  defined _BSD_SOURCE \
   ||  defined _SVID_SOURCE
   /*
    * but where any of these source code qualifiers are specified,
    * then assume ANSI I/O standards are preferred over Microsoft's...
    */
#  define __USE_MINGW_ANSI_STDIO    1
# else
   /* otherwise use whatever __MINGW_FEATURES__ specifies...
    */
#  define __USE_MINGW_ANSI_STDIO    (__MINGW_FEATURES__ & __MINGW_ANSI_STDIO__)
# endif
#endif

#ifndef _POSIX_C_SOURCE
 /* Users may define this, either directly or indirectly, to explicitly
  * enable a particular level of visibility for the subset of those POSIX
  * features which are supported by MinGW; (notice that this offers no
  * guarantee that any particular POSIX feature will be supported).
  */
# if defined _XOPEN_SOURCE
  /* Specifying this is the preferred method for setting _POSIX_C_SOURCE;
   * (POSIX defines an explicit relationship to _XOPEN_SOURCE).  Note that
   * any such explicit setting will augment the set of features which are
   * available to any compilation unit, even if it seeks to be strictly
   * ANSI-C compliant.
   */
#  if _XOPEN_SOURCE < 500
#   define _POSIX_C_SOURCE  1L      /* POSIX.1-1990 / SUSv1 */

#  elif _XOPEN_SOURCE < 600
#   define _POSIX_C_SOURCE  199506L /* POSIX.1-1996 / SUSv2 */

#  elif _XOPEN_SOURCE < 700
#   define _POSIX_C_SOURCE  200112L /* POSIX.1-2001 / SUSv3 */

#  else
#   define _POSIX_C_SOURCE  200809L /* POSIX.1-2008 / SUSv4 */
#  endif

# elif defined _GNU_SOURCE || defined _BSD_SOURCE || ! defined __STRICT_ANSI__
  /*
   * No explicit level of support has been specified; implicitly grant
   * the most comprehensive level to any compilation unit which requests
   * either GNU or BSD feature support, or does not seek to be strictly
   * ANSI-C compliant.
   */
#  define _POSIX_C_SOURCE  200809L

# elif defined _POSIX_SOURCE
  /* Now formally deprecated by POSIX, some old code may specify this;
   * it will enable a minimal level of POSIX support, in addition to the
   * limited feature set enabled for strict ANSI-C conformity.
   */
#  define _POSIX_C_SOURCE  1L
# endif
#endif

#ifndef _ISOC99_SOURCE
 /* libmingwex.a provides free-standing implementations for many of the
  * functions which were introduced in C99; MinGW headers do not expose
  * prototypes for these, unless this feature test macro is defined, by
  * the user, or implied by other standards...
  */
# if __STDC_VERSION__ >= 199901L || _POSIX_C_SOURCE >= 200112L
#  define _ISOC99_SOURCE  1
# endif
#endif

#if ! defined _MINGW32_SOURCE_EXTENDED && ! defined __STRICT_ANSI__
/*
 * Enable mingw32 extensions by default, except when __STRICT_ANSI__
 * conformity mode has been enabled.
 */
# define _MINGW32_SOURCE_EXTENDED  1
#endif

#endif /* __MINGW_H: $RCSfile: _mingw.h.in,v $: end of file */

O restante das inclusões deve ser padrão para o seu ambiente.

Sim, existe: https://github.com/robinrowe/libunistd

Clone o repositório e inclua path\to\libunistd\unistdna INCLUDEvariável de ambiente.

O equivalente unistd.hno Windows éwindows.h

Crie seu próprio cabeçalho unistd.h e inclua os cabeçalhos necessários para os protótipos de funções.