使用两个简单的技巧检测操作系统：
ifeq ($(OS),Windows_NT) # is Windows_NT on XP, 2000, 7, Vista, 10...
detected_OS := Windows
else
detected_OS := $(shell uname) # same as "uname -s"
endif
或者更安全的方式，如果不在 Windows 上且不uname可用：
ifeq ($(OS),Windows_NT)
detected_OS := Windows
else
detected_OS := $(shell sh -c 'uname 2>/dev/null || echo Unknown')
endif
如果您想区分 Cygwin/MinGW/MSYS/Windows，Ken Jackson提出了一个有趣的替代方案。看看他的回答是这样的：
ifeq '$(findstring ;,$(PATH))' ';'
detected_OS := Windows
else
detected_OS := $(shell uname 2>/dev/null || echo Unknown)
detected_OS := $(patsubst CYGWIN%,Cygwin,$(detected_OS))
detected_OS := $(patsubst MSYS%,MSYS,$(detected_OS))
detected_OS := $(patsubst MINGW%,MSYS,$(detected_OS))
endif
然后您可以根据以下内容选择相关内容detected_OS：
ifeq ($(detected_OS),Windows)
CFLAGS += -D WIN32
endif
ifeq ($(detected_OS),Darwin) # Mac OS X
CFLAGS += -D OSX
endif
ifeq ($(detected_OS),Linux)
CFLAGS += -D LINUX
endif
ifeq ($(detected_OS),GNU) # Debian GNU Hurd
CFLAGS += -D GNU_HURD
endif
ifeq ($(detected_OS),GNU/kFreeBSD) # Debian kFreeBSD
CFLAGS += -D GNU_kFreeBSD
endif
ifeq ($(detected_OS),FreeBSD)
CFLAGS += -D FreeBSD
endif
ifeq ($(detected_OS),NetBSD)
CFLAGS += -D NetBSD
endif
ifeq ($(detected_OS),DragonFly)
CFLAGS += -D DragonFly
endif
ifeq ($(detected_OS),Haiku)
CFLAGS += -D Haiku
endif
笔记：
下面我提供了一个使用make和gcc构建共享库的完整示例：*.so或*.dll取决于平台。该示例尽可能简单以便更易于理解。
要在 Windows 上安装make和安装，gcc请参阅Cygwin或MinGW。
我的示例基于五个文件
├── lib
│ └── Makefile
│ └── hello.h
│ └── hello.c
└── app
└── Makefile
└── main.c
提醒： Makefile使用制表缩进。复制粘贴下面的示例文件时要小心。
两个Makefile文件
1.lib/Makefile
ifeq ($(OS),Windows_NT)
uname_S := Windows
else
uname_S := $(shell uname -s)
endif
ifeq ($(uname_S), Windows)
target = hello.dll
endif
ifeq ($(uname_S), Linux)
target = libhello.so
endif
#ifeq ($(uname_S), .....) #See https://stackoverflow.com/a/27776822/938111
# target = .....
#endif
%.o: %.c
gcc -c $< -fPIC -o $@
# -c $< => $< is first file after ':' => Compile hello.c
# -fPIC => Position-Independent Code (required for shared lib)
# -o $@ => $@ is the target => Output file (-o) is hello.o
$(target): hello.o
gcc $^ -shared -o $@
# $^ => $^ expand to all prerequisites (after ':') => hello.o
# -shared => Generate shared library
# -o $@ => Output file (-o) is $@ (libhello.so or hello.dll)
2.app/Makefile
ifeq ($(OS),Windows_NT)
uname_S := Windows
else
uname_S := $(shell uname -s)
endif
ifeq ($(uname_S), Windows)
target = app.exe
endif
ifeq ($(uname_S), Linux)
target = app
endif
#ifeq ($(uname_S), .....) #See https://stackoverflow.com/a/27776822/938111
# target = .....
#endif
%.o: %.c
gcc -c $< -I ../lib -o $@
# -c $< => compile (-c) $< (first file after :) = main.c
# -I ../lib => search headers (*.h) in directory ../lib
# -o $@ => output file (-o) is $@ (target) = main.o
$(target): main.o
gcc $^ -L../lib -lhello -o $@
# $^ => $^ (all files after the :) = main.o (here only one file)
# -L../lib => look for libraries in directory ../lib
# -lhello => use shared library hello (libhello.so or hello.dll)
# -o $@ => output file (-o) is $@ (target) = "app.exe" or "app"
要了解更多信息，请阅读cfi指出的自动变量文档。
源代码
-lib/hello.h
#ifndef HELLO_H_
#define HELLO_H_
const char* hello();
#endif
-lib/hello.c
#include "hello.h"
const char* hello()
{
return "hello";
}
-app/main.c
#include "hello.h" //hello()
#include <stdio.h> //puts()
int main()
{
const char* str = hello();
puts(str);
}
构建
Makefile修复（用一个列表替换前导空格）的复制粘贴。
> sed 's/^ */\t/' -i */Makefile
该make命令在两个平台上是相同的。给定的输出在类 Unix 操作系统上：
> make -C lib
make: Entering directory '/tmp/lib'
gcc -c hello.c -fPIC -o hello.o
# -c hello.c => hello.c is first file after ':' => Compile hello.c
# -fPIC => Position-Independent Code (required for shared lib)
# -o hello.o => hello.o is the target => Output file (-o) is hello.o
gcc hello.o -shared -o libhello.so
# hello.o => hello.o is the first after ':' => Link hello.o
# -shared => Generate shared library
# -o libhello.so => Output file (-o) is libhello.so (libhello.so or hello.dll)
make: Leaving directory '/tmp/lib'
> make -C app
make: Entering directory '/tmp/app'
gcc -c main.c -I ../lib -o main.o
# -c main.c => compile (-c) main.c (first file after :) = main.cpp
# -I ../lib => search headers (*.h) in directory ../lib
# -o main.o => output file (-o) is main.o (target) = main.o
gcc main.o -L../lib -lhello -o app
# main.o => main.o (all files after the :) = main.o (here only one file)
# -L../lib => look for libraries in directory ../lib
# -lhello => use shared library hello (libhello.so or hello.dll)
# -o app => output file (-o) is app.exe (target) = "app.exe" or "app"
make: Leaving directory '/tmp/app'
运行
应用程序需要知道共享库在哪里。
在 Windows 上，一个简单的解决方案是复制应用程序所在的库：
> cp -v lib/hello.dll app
`lib/hello.dll' -> `app/hello.dll'
在类 Unix 操作系统上，您可以使用LD_LIBRARY_PATH环境变量：
> export LD_LIBRARY_PATH=lib
在 Windows 上运行命令：
> app/app.exe
hello
在类 Unix 操作系统上运行命令：
> app/app
hello