因为 C++ 具有跨平台的特性,所以有些需求一套代码就多端使用,比如我最近在学习的 OpenGL ES。
但是,不同平台还是具有一定差异性,所以我们首先得判断出是什么平台? 比如 iOS 系统和 Android 系统。
那么如何判断呢?我们接着往下看!
要检查 C 或 C 代码中主机的操作系统,我们需要检查编译器(GNU GCC 或 G )定义的宏。 例如,在 Windows 平台上,编译器定义了一个名为 _WIN32 的特殊宏。 因此,如果定义了宏 _WIN32,我们就在 Windows 上。 同样,其他操作系统也有编译器定义的特定宏。
C++ 编译器预定义了某些全局标识符,称为 manifest constants
。大多数全局标识符以两个下划线 (__
) 开头和结尾。
检查 Windows 操作系统的示例:
#ifdef _WIN32
printf("You have Windows Operating System");
#endif
2.1 宏定义列表
以下是基于操作系统定义的宏列表:
操作系统 | 宏定义 | 说明 |
---|---|---|
Windows 32 bit + 64 bit | _WIN32 |
for all Windows OS |
Windows 64 bit | _WIN64 |
Only for 64 bit Windows |
Apple | __APPLE__ |
for all Apple OS |
Apple | __MACH__ |
alternative to above |
iOS embedded | TARGET_OS_EMBEDDED |
include TargetConditionals.h |
iOS stimulator | TARGET_IPHONE_SIMULATOR |
include TargetConditionals.h |
iPhone | TARGET_OS_IPHONE |
include TargetConditionals.h |
MacOS | TARGET_OS_MAC |
include TargetConditionals.h |
Android | __ANDROID__ |
subset of linux |
Unix based OS | __unix__ |
|
Linux | __linux__ |
subset of unix |
POSIX based | _POSIX_VERSION |
Windows with Cygwin |
Solaris | __sun |
|
HP UX | __hpux |
|
BSD | BSD |
all BSD flavors |
DragonFly BSD | __DragonFly__ |
|
FreeBSD | __FreeBSD__ |
|
NetBSD | __NetBSD__ |
|
OpenBSD | __OpenBSD__ |
请注意,宏对 GNU GCC 和 G++ 有效,并且可能因其他编译器而异。 我们将通过一些基本示例,并探讨这些功能在现实生活中的使用。
关于更多的宏定义可以参考下面的两个链接:
2.2 示例: 检测 64
位 Windows
操作系统或 32
位 Windows
操作系统
在下面的示例中,我们专注于检测我们正在运行的 Windows 的风格,它可以是 64 位或 32 位。对于 Windows,我们的表格将是:
操作系统 | 宏定义 |
---|---|
Windows OS 32 bit + 64 bit | _WIN32 |
Windows OS 64 bit | _WIN64 |
由于 _WIN32
在 32
位和 64
位 Windows
操作系统中都存在,
所以我们需要先检查 _WIN32
的存在以确认它是 Windows
操作系统,
然后再检查 _WIN64
的存在以确认它是否是 64
位 Windows
操作系统或 32
位 Windows
操作系统。
以下是检查您的 Windows 操作系统的代码:
#include <stdio.h>
int main()
{
#ifdef _WIN32 // Includes both 32 bit and 64 bit
#ifdef _WIN64
printf("Windows 64 bit\n");
#else
printf("Windows 32 bit\n");
#endif
#else
printf("Not a Windows OS\n");
#endif
return 0;
}
运行输出
Windows 32 bit
2.3 示例:检测苹果操作系统是MacOS
还是 iPhone
在此示例中,我们使用 Apple OS
的宏来检测正在使用的 Apple OS
,如 MacOS
或 iPhone
。
#include <stdio.h>
int main()
{
#if __APPLE__
#include "TargetConditionals.h"
#if TARGET_OS_IPHONE && TARGET_IPHONE_SIMULATOR
printf("iPhone stimulator\n");
#elif TARGET_OS_IPHONE
printf("iPhone\n");
#elif TARGET_OS_MAC
printf("MacOS\n");
#else
printf("Other Apple OS\n");
#endif
#else
printf("Not an Apple OS\n");
#endif
return 0;
}
运行输出
MacOS
2.4 普通示例
#include <stdio.h>
int main() {
#ifdef _WIN32
printf("Windows\n");
#elif __linux__
printf("Linux\n");
#elif __unix__
printf("Other unix OS\n");
#else
printf("Unidentified OS\n");
#endif
return 0;
}
2.5 作用
凭借检测语言(在我们的案例中为 C 和 C++)中的操作系统的能力,我们可以编写一个跨平台代码,通过分离平台相关代码来在所有平台上运行。
#include <stdio.h>
int main()
{
#if __APPLE__
// apple specific code
#elif _WIN32
// windows specific code
#elif __LINUX__
// linux specific code
#elif BSD
// BSD specific code
#else
// general code or warning
#endif
// general code
return 0;
}
同时,我们可以编写针对特定平台优化的代码。
例如,一个函数调用可能在所有平台上都受支持,但我们可以针对特定平台(例如 Linux
)对其进行大幅优化,但是这个新代码会在其他平台上引发错误。 在这种情况下,我们可以使用宏来检测它是否是 Linux
,对于这种情况,我们可以轻松地使用其他替代优化代码。
例如:
#include <stdio.h>
int main()
{
#if __linux__
// linux optimized code (will fail in other platforms)
#else
// general code for all platforms
#endif
// general code
return 0;
}
3.1 一个简单的判断
#if defined(WIN32) || defined(_WIN32) || defined(__WIN32__) || defined(__NT__)
//define something for Windows (32-bit and 64-bit, this part is common)
#ifdef _WIN64
//define something for Windows (64-bit only)
#else
//define something for Windows (32-bit only)
#endif
#elif __APPLE__
#include <TargetConditionals.h>
#if TARGET_IPHONE_SIMULATOR
// iOS, tvOS, or watchOS Simulator
#elif TARGET_OS_MACCATALYST
// Mac's Catalyst (ports iOS API into Mac, like UIKit).
#elif TARGET_OS_IPHONE
// iOS, tvOS, or watchOS device
#elif TARGET_OS_MAC
// Other kinds of Apple platforms
#else
# error "Unknown Apple platform"
#endif
#elif __linux__
// linux
#elif __unix__ // all unices not caught above
// Unix
#elif defined(_POSIX_VERSION)
// POSIX
#else
# error "Unknown compiler"
#endif
3.2 优秀的 googletest 的示例
https://github.com/google/googletest/blob/main/googletest/include/gtest/internal/gtest-port-arch.h
// Copyright 2015, Google Inc.
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
// The Google C++ Testing and Mocking Framework (Google Test)
//
// This header file defines the GTEST_OS_* macro.
// It is separate from gtest-port.h so that custom/gtest-port.h can include it.
#ifndef GOOGLETEST_INCLUDE_GTEST_INTERNAL_GTEST_PORT_ARCH_H_
#define GOOGLETEST_INCLUDE_GTEST_INTERNAL_GTEST_PORT_ARCH_H_
// Determines the platform on which Google Test is compiled.
#ifdef __CYGWIN__
#define GTEST_OS_CYGWIN 1
#elif defined(__MINGW__) || defined(__MINGW32__) || defined(__MINGW64__)
#define GTEST_OS_WINDOWS_MINGW 1
#define GTEST_OS_WINDOWS 1
#elif defined _WIN32
#define GTEST_OS_WINDOWS 1
#ifdef _WIN32_WCE
#define GTEST_OS_WINDOWS_MOBILE 1
#elif defined(WINAPI_FAMILY)
#include <winapifamily.h>
#if WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_DESKTOP)
#define GTEST_OS_WINDOWS_DESKTOP 1
#elif WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_PHONE_APP)
#define GTEST_OS_WINDOWS_PHONE 1
#elif WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_APP)
#define GTEST_OS_WINDOWS_RT 1
#elif WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_TV_TITLE)
#define GTEST_OS_WINDOWS_PHONE 1
#define GTEST_OS_WINDOWS_TV_TITLE 1
#else
// WINAPI_FAMILY defined but no known partition matched.
// Default to desktop.
#define GTEST_OS_WINDOWS_DESKTOP 1
#endif
#else
#define GTEST_OS_WINDOWS_DESKTOP 1
#endif // _WIN32_WCE
#elif defined __OS2__
#define GTEST_OS_OS2 1
#elif defined __APPLE__
#define GTEST_OS_MAC 1
#include <TargetConditionals.h>
#if TARGET_OS_IPHONE
#define GTEST_OS_IOS 1
#endif
#elif defined __DragonFly__
#define GTEST_OS_DRAGONFLY 1
#elif defined __FreeBSD__
#define GTEST_OS_FREEBSD 1
#elif defined __Fuchsia__
#define GTEST_OS_FUCHSIA 1
#elif defined(__GNU__)
#define GTEST_OS_GNU_HURD 1
#elif defined(__GLIBC__) && defined(__FreeBSD_kernel__)
#define GTEST_OS_GNU_KFREEBSD 1
#elif defined __linux__
#define GTEST_OS_LINUX 1
#if defined __ANDROID__
#define GTEST_OS_LINUX_ANDROID 1
#endif
#elif defined __MVS__
#define GTEST_OS_ZOS 1
#elif defined(__sun) && defined(__SVR4)
#define GTEST_OS_SOLARIS 1
#elif defined(_AIX)
#define GTEST_OS_AIX 1
#elif defined(__hpux)
#define GTEST_OS_HPUX 1
#elif defined __native_client__
#define GTEST_OS_NACL 1
#elif defined __NetBSD__
#define GTEST_OS_NETBSD 1
#elif defined __OpenBSD__
#define GTEST_OS_OPENBSD 1
#elif defined __QNX__
#define GTEST_OS_QNX 1
#elif defined(__HAIKU__)
#define GTEST_OS_HAIKU 1
#elif defined ESP8266
#define GTEST_OS_ESP8266 1
#elif defined ESP32
#define GTEST_OS_ESP32 1
#elif defined(__XTENSA__)
#define GTEST_OS_XTENSA 1
#endif // __CYGWIN__
#endif // GOOGLETEST_INCLUDE_GTEST_INTERNAL_GTEST_PORT_ARCH_H_
这个示例通过判断系统预定的宏定义,然后重新定义了一些宏定义,方便后续业务直接判断,如下所示:
通过以上的知识,我们知道了 C++ 如何通过宏定义来判断不同的操作系统,方便后续对不同的平台做一些差异性的业务。
CMake 能够用来在 Window、Linux、Mac 平台下进行编译,在它的内部也定义了和这些平台相关的变量。
具体查看 官方文档 。
列举一些常见的:
- WIN32
- 如果编译的目标系统是 Window, 包括 WIN64,那么 WIN32 为 True 。
- UNIX
- 如果编译的目标系统是 Unix 或者类 Unix 也就是 Linux , 那么 UNIX 为 True 。
- MSVC
- 如果编译器是 Window 上的 Visual C++ 之类的,那么 MSVC 为 True 。
- ANDROID
- Set to 1 when the target system (CMAKE_SYSTEM_NAME) is Android.
- APPLE
- Set to True when the target system is an Apple platform (macOS, iOS, tvOS or watchOS).
有了这些常量做区分,就可以在一份 CMake 文件中编写不同平台的编译选项。
if(ANDROID){
# do something
}elseif(APPLE){
# do something
}
更多可以参考链接:
- https://cmake.org/cmake/help/v3.12/manual/cmake-variables.7.html
- Android NDK 开发之 CMake 必知必会
- https://docwiki.embarcadero.com/RADStudio/Sydney/en/Predefined_Macros
- https://sourceforge.net/p/predef/wiki/OperatingSystems/
- https://stackoverflow.com/questions/5919996/how-to-detect-reliably-mac-os-x-ios-linux-windows-in-c-preprocessor
- https://github.com/google/googletest/blob/main/googletest/include/gtest/internal/gtest-port-arch.h
- https://iq.opengenus.org/detect-operating-system-in-c/
https://ouyangpeng.blog.csdn.net/article/details/124703411?spm=1001.2101.3001.6661.1&depth_1-utm_source=distribute.pc_relevant_t0.none-task-blog-2%7Edefault%7ECTRLIST%7Edefault-1-124703411-blog-70143942.pc_relevant_multi_platform_whitelistv1