舊博文，搬到 csdn
原文：http://rebootcat.com/2020/08/30/scons/

前言

我是一個(gè) linux c++ 開(kāi)發(fā)者，但是一直對(duì) Makefile 的語(yǔ)法很是頭痛，每次都記不住，所以每次寫 Makefile 都很痛苦，Makefile 里需要你自己編寫依賴和推導(dǎo)規(guī)則，這個(gè)過(guò)程能不能簡(jiǎn)單點(diǎn)呢？

對(duì)于編譯一個(gè) C++ 工程來(lái)說(shuō)，也許需要的就是頭文件路徑、庫(kù)路徑、編譯參數(shù)，剩下的東西基本也不重要，這三樣足夠去編譯一個(gè)工程了。所以有沒(méi)有一個(gè)工具能簡(jiǎn)單點(diǎn)的去實(shí)現(xiàn) C++ 項(xiàng)目的構(gòu)建呢？

答案是有的，Scons 就是答案。

Scons

什么是 scons

這里直接引用官網(wǎng)的解釋：

What is SCons?

SCons is an Open Source software construction tool—that is, a next-generation build tool. Think of SCons as an improved, cross-platform substitute for the classic Make utility with integrated functionality similar to autoconf/automake and compiler caches such as ccache. In short, SCons is an easier, more reliable and faster way to build software.

What makes SCons better?

• Configuration files are Python scripts–use the power of a real programming language to solve build problems.
• Reliable, automatic dependency analysis built-in for C, C++ and Fortran–no more “make depend” or “make clean” to get all of the dependencies. Dependency analysis is easily extensible through user-defined dependency Scanners for other languages or file types.
• Built-in support for C, C++, D, Java, Fortran, Yacc, Lex, Qt and SWIG, and building TeX and LaTeX documents. Easily extensible through user-defined Builders for other languages or file types.
• Building from central repositories of source code and/or pre-built targets.
• Built-in support for fetching source files from SCCS, RCS, CVS, BitKeeper and Perforce.
• Built-in support for Microsoft Visual Studio .NET and past Visual Studio versions, including generation of .dsp, .dsw, .sln and .vcproj files.
• Reliable detection of build changes using MD5 signatures; optional, configurable support for traditional timestamps.
• Improved support for parallel builds–like make -j but keeps N jobs running simultaneously regardless of directory hierarchy.
• Integrated Autoconf-like support for finding #include files, libraries, functions and typedefs.
• Global view of all dependencies–no more multiple build passes or reordering targets to build everything.
• Ability to share built files in a cache to speed up multiple builds–like ccache but for any type of target file, not just C/C++ compilation.
• Designed from the ground up for cross-platform builds, and known to work on Linux, other POSIX systems (including AIX, BSD systems, HP/UX, IRIX and Solaris), Windows NT, Mac OS X, and OS/2.

最大特點(diǎn)就是使用 Python 語(yǔ)法來(lái)編寫編譯構(gòu)建腳本，并且支持依賴自動(dòng)推導(dǎo)，支持編譯 C/C++/D/Java/Fortran等項(xiàng)目，并且是跨平臺(tái)的(因?yàn)?python 是跨平臺(tái)的）。

所以如果你對(duì) python 熟悉的話，而且你和我對(duì) C++ Makefile 有一樣的煩惱，那么這對(duì)你將是一個(gè)好消息。 你將可以用 python 來(lái)編寫構(gòu)建腳本，而且會(huì)很簡(jiǎn)單，對(duì)于復(fù)雜的大型項(xiàng)目也能快速構(gòu)建好。（也許只要 30 分鐘）

安裝 scons

因?yàn)?scons 是基于 python 來(lái)構(gòu)建的，所以毋容置疑，首先是需要準(zhǔn)備好 python 環(huán)境，然后使用下述命令安裝 scons 工具。

pip install scons

scons 使用語(yǔ)法

注：本文以一個(gè)多源文件，多目錄結(jié)構(gòu)的項(xiàng)目 mux 為例，介紹 cmake 的使用，相關(guān)源文件以及cmake 腳本可以直接查看源項(xiàng)目。

scons 構(gòu)建腳本由一個(gè) SConstruct 文件和多個(gè) SConscript 文件構(gòu)成。

SConstruct 通常位于項(xiàng)目頂層目錄，然后 SConscript 通常位于子目錄（子模塊）。

那么來(lái)看一下 SConstruct 腳本長(zhǎng)啥樣?

SConstruct

#!/usr/bin/env python
#-*- coding:utf-8 -*-import sys
import os
import platform
import reenv = Environment()
abs_path = os.getcwd()
print('workspace path:{0}'.format(abs_path))sbuild_dir = 'sbuild'headers = ['.', 'third-party/include']
libs = ['./third-party/lib']abs_headers = []
abs_libs = []for item in headers:abs_item = os.path.join(abs_path, item)abs_headers.append(abs_item)for item in libs:abs_item = os.path.join(abs_path, item)abs_libs.append(abs_item)build_dir = os.path.join(abs_path, sbuild_dir)
abs_libs.append(os.path.join(build_dir, 'lib'))CCFLAGS = '-ggdb -std=c++11'print('\nheaders path:')
print(abs_headers)
print('\n')print('libs path:')
print(abs_libs)
print('\n')print("begin load SConscript")env["headers"] = abs_headers
env["libs"]    = abs_libs
env["MUX_DIR"] = abs_path
env['ccflags'] = CCFLAGS
env['build_dir'] = build_dirExport('env')SConscript(['./mbase/SConscript'])
SConscript(['./message_handle/SConscript'])
SConscript(['./epoll/SConscript'])
SConscript(['./transport/SConscript'])
SConscript(['./demo/bench/SConscript'])
SConscript(['./demo/echo/SConscript'])print("\n All Done, Please Check {0}".format(env['build_dir']))

來(lái)分析一下這個(gè)文件，源文件可以直接在 我的github下載。

SConstruct 文件主要做了兩件事：

• env 環(huán)境變量的構(gòu)造，主要是頭文件路徑，庫(kù)路徑，編譯參數(shù)，自定義的一些變量等
• 使用 SConscript 函數(shù)解析執(zhí)行子模塊的 SConscript 文件

需要注意的是 SConstruct 和 SConscript 共享變量使用的就是 env 這個(gè)變量，你可以看到上面有一句：

Export('env')

這句很重要。

SConscript

那么位于子模塊或者子目錄的 SConscript 文件長(zhǎng)啥樣呢？

#!/usr/bin/env python
#-*- coding:utf-8 -*-import os
import sysImport('env')
project_dir  = env['MUX_DIR']epoll_lib  = 'epoll'epoll_src_path = os.path.join(project_dir, 'epoll/src')
epoll_sources = []
for item in os.listdir(epoll_src_path):if item.endswith('.cc') or item.endswith('.cpp') or item.endswith('.cxx'):abs_item = os.path.join(epoll_src_path, item)epoll_sources.append(abs_item)print('\nbuild target:lib{0}.a'.format(epoll_lib))
print(epoll_sources)lib_dir = os.path.join(env['build_dir'], 'lib')link_libraries = ['mbase']
for lib_name in link_libraries:lib_name = "{0}{1}{2}".format(env['LIBPREFIX'], lib_name, env['LIBSUFFIX'])abs_lib_name = os.path.join(lib_dir, lib_name)epoll_sources.append(abs_lib_name)env.StaticLibrary(target = os.path.join(lib_dir, epoll_lib),source  = epoll_sources,CPPPATH = env['headers'], # includeLIBPATH = env['libs'],    # lib pathLIBS    = ['pthread'],    # link libCCFLAGS = env['ccflags'])

來(lái)分析一下這個(gè)文件，源文件可以直接在 我的github下載。

SConscript 主要做了兩件事：

• 構(gòu)造一個(gè)源文件列表（用來(lái)構(gòu)建 target 所需要使用的源文件）
• 根據(jù)需要構(gòu)建 static_lib/dynamic_lib/binary

當(dāng)然，還有一點(diǎn)很重要，上面其實(shí)提到了，SConscript 和 SConstruct 用來(lái)共享變量使用的是 env 這個(gè)變量，所以你可以看到一句很重要的：

Import('env')

構(gòu)造源文件列表，對(duì)于 Python 來(lái)說(shuō)，簡(jiǎn)直是小菜一碟，太簡(jiǎn)單了；

然后如何生成目標(biāo)文件呢？

1 生成二進(jìn)制文件

env.Program(target = os.path.join(bin_dir, echo_server_bin),source  = echo_server_sources,CPPPATH = env['headers'],LIBPATH = env['libs'],LIBS    = ['transport','msghandler','epoll', 'mbase', 'pthread'],CCFLAGS = env['ccflags'])

2 生成靜態(tài)庫(kù)

env.StaticLibrary(target = os.path.join(lib_dir, epoll_lib),source  = epoll_sources,CPPPATH = env['headers'], # includeLIBPATH = env['libs'],    # lib pathLIBS    = ['pthread'],    # link libCCFLAGS = env['ccflags'])

3 生成動(dòng)態(tài)庫(kù)

env.SharedLibrary(target = os.path.join(lib_dir, epoll_lib),source  = epoll_sources,CPPPATH = env['headers'], # includeLIBPATH = env['libs'],    # lib pathLIBS    = ['pthread'],    # link libCCFLAGS = env['ccflags'])

上面 3 個(gè)函數(shù)的參數(shù)都是類似的：

• target: 指定需要生成的目標(biāo)文件，通常我自己會(huì)寫一個(gè)絕對(duì)路徑；對(duì)于 lib 來(lái)說(shuō)只需要寫名字就行，前綴和后綴不需要寫。(eg. target = ‘/root/scons_repo/sbuild/lib/test’ ，會(huì)生成 /root/scons_repo/sbuild/lib/libtest.a)
• source: 編譯目標(biāo)文件需要的源文件列表
• CPPPATH: 通常就是需要 Include 的頭文件路徑
• LIBPATH: 通常就是需要鏈接的庫(kù)路徑
• LIBS: 需要鏈接的庫(kù)列表
• CCFLAGS: 編譯參數(shù)

attention:

上面有一個(gè)坑我自己碰到的，當(dāng)我構(gòu)建目標(biāo)生成一個(gè)靜態(tài)庫(kù)的時(shí)候，需要鏈接其他的靜態(tài)庫(kù)，如果使用 $LIBPATH 和 $LIBS 指定鏈接庫(kù)的話，scons 并沒(méi)有鏈接這些庫(kù)。嘗試了很多方法，搜索了很多，也沒(méi)有解決這個(gè)問(wèn)題。

最后是這樣解決的。把需要鏈接的靜態(tài)庫(kù)添加到 source 參數(shù)中，和其他 cc/cpp 源文件一樣放在一起，并且這些庫(kù)需要使用絕對(duì)路徑。

通常為了跨平臺(tái)的方便，需要考慮lib 的前后綴，可以這樣寫：

link_libraries = ['test1', 'test2']
for lib_name in link_libraries:lib_name = "{0}{1}{2}".format(env['LIBPREFIX'], lib_name, env['LIBSUFFIX'])abs_lib_name = os.path.join(lib_dir, lib_name)sources.append(abs_lib_name)

scons 命令

上面詳細(xì)講解了如何使用 python 編寫構(gòu)建腳本，那么寫好之后怎么用呢？

常用的幾個(gè)命令：

編譯：

scons

如果需要并行編譯：

scons -j4

清理：

scons -c

然后就會(huì)按照你腳本里寫的方式去構(gòu)建目標(biāo)了。

這里貼一下 我的項(xiàng)目 編譯的輸出：

$ scons
scons: Reading SConscript files ...
workspace path:/mnt/centos-share/workspace/muxheaders path:
['/mnt/centos-share/workspace/mux/.', '/mnt/centos-share/workspace/mux/third-party/include']libs path:
['/mnt/centos-share/workspace/mux/./third-party/lib', '/mnt/centos-share/workspace/mux/sbuild/lib']begin load SConscriptbuild target:libmbase.a
['/mnt/centos-share/workspace/mux/mbase/src/packet.cc']build target:libmsghandler.a
['/mnt/centos-share/workspace/mux/message_handle/src/message_handler.cc']build target:libepoll.a
['/mnt/centos-share/workspace/mux/epoll/src/epoll_tcp_client.cc', '/mnt/centos-share/workspace/mux/epoll/src/epoll_tcp_server.cc']build target:libtransport.a
['/mnt/centos-share/workspace/mux/transport/src/tcp_transport.cc']build target:bench_server
['bench_server.cc']build target:bench_client
['client.cc']build target:echo_server
['echo_server.cc']build target:echo_client
['client.cc']All Done, Please Check /mnt/centos-share/workspace/mux/sbuild
scons: done reading SConscript files.
scons: Building targets ...
g++ -o demo/bench/bench_server.o -c -ggdb -std=c++11 -I. -Ithird-party/include demo/bench/bench_server.cc
g++ -o demo/bench/client.o -c -ggdb -std=c++11 -I. -Ithird-party/include demo/bench/client.cc
g++ -o demo/echo/client.o -c -ggdb -std=c++11 -I. -Ithird-party/include demo/echo/client.cc
g++ -o demo/echo/echo_server.o -c -ggdb -std=c++11 -I. -Ithird-party/include demo/echo/echo_server.cc
g++ -o epoll/src/epoll_tcp_client.o -c -ggdb -std=c++11 -I. -Ithird-party/include epoll/src/epoll_tcp_client.cc
g++ -o epoll/src/epoll_tcp_server.o -c -ggdb -std=c++11 -I. -Ithird-party/include epoll/src/epoll_tcp_server.cc
g++ -o mbase/src/packet.o -c -ggdb -std=c++11 -I. -Ithird-party/include mbase/src/packet.cc
g++ -o message_handle/src/message_handler.o -c -ggdb -std=c++11 -I. -Ithird-party/include message_handle/src/message_handler.cc
g++ -o transport/src/tcp_transport.o -c -ggdb -std=c++11 -I. -Ithird-party/include transport/src/tcp_transport.cc
ar rc sbuild/lib/libmbase.a mbase/src/packet.o
ranlib sbuild/lib/libmbase.a
ar rc sbuild/lib/libepoll.a epoll/src/epoll_tcp_client.o epoll/src/epoll_tcp_server.o sbuild/lib/libmbase.a
ranlib sbuild/lib/libepoll.a
ar rc sbuild/lib/libtransport.a transport/src/tcp_transport.o sbuild/lib/libepoll.a sbuild/lib/libmbase.a
ranlib sbuild/lib/libtransport.a
ar rc sbuild/lib/libmsghandler.a message_handle/src/message_handler.o sbuild/lib/libmbase.a
ranlib sbuild/lib/libmsghandler.a
g++ -o sbuild/bin/bench_client demo/bench/client.o -Lthird-party/lib -Lsbuild/lib -ltransport -lmsghandler -lepoll -lmbase -lpthread
g++ -o sbuild/bin/bench_server demo/bench/bench_server.o -Lthird-party/lib -Lsbuild/lib -ltransport -lmsghandler -lepoll -lmbase -lpthread
g++ -o sbuild/bin/echo_client demo/echo/client.o -Lthird-party/lib -Lsbuild/lib -ltransport -lmsghandler -lepoll -lmbase -lpthread
g++ -o sbuild/bin/echo_server demo/echo/echo_server.o -Lthird-party/lib -Lsbuild/lib -ltransport -lmsghandler -lepoll -lmbase -lpthread
scons: done building targets.

$ scons -c
scons: Reading SConscript files ...
workspace path:/mnt/centos-share/workspace/muxheaders path:
['/mnt/centos-share/workspace/mux/.', '/mnt/centos-share/workspace/mux/third-party/include']libs path:
['/mnt/centos-share/workspace/mux/./third-party/lib', '/mnt/centos-share/workspace/mux/sbuild/lib']begin load SConscriptbuild target:libmbase.a
['/mnt/centos-share/workspace/mux/mbase/src/packet.cc']build target:libmsghandler.a
['/mnt/centos-share/workspace/mux/message_handle/src/message_handler.cc']build target:libepoll.a
['/mnt/centos-share/workspace/mux/epoll/src/epoll_tcp_client.cc', '/mnt/centos-share/workspace/mux/epoll/src/epoll_tcp_server.cc']build target:libtransport.a
['/mnt/centos-share/workspace/mux/transport/src/tcp_transport.cc']build target:bench_server
['bench_server.cc']build target:bench_client
['client.cc']build target:echo_server
['echo_server.cc']build target:echo_client
['client.cc']All Done, Please Check /mnt/centos-share/workspace/mux/sbuild
scons: done reading SConscript files.
scons: Cleaning targets ...
Removed demo/bench/bench_server.o
Removed demo/bench/client.o
Removed demo/echo/client.o
Removed demo/echo/echo_server.o
Removed epoll/src/epoll_tcp_client.o
Removed epoll/src/epoll_tcp_server.o
Removed mbase/src/packet.o
Removed message_handle/src/message_handler.o
Removed transport/src/tcp_transport.o
Removed sbuild/lib/libmbase.a
Removed sbuild/lib/libepoll.a
Removed sbuild/lib/libtransport.a
Removed sbuild/lib/libmsghandler.a
Removed sbuild/bin/bench_client
Removed sbuild/bin/bench_server
Removed sbuild/bin/echo_client
Removed sbuild/bin/echo_server
scons: done cleaning targets.

寫在最后

scons 使用 python 腳本來(lái)構(gòu)建項(xiàng)目，如果對(duì) python 熟悉的話，那么編寫編譯構(gòu)建腳本將會(huì)大大提高效率，再也不用局限在 Makefile 的蛋疼語(yǔ)法里面了。

當(dāng)然 scons 的缺點(diǎn)也有，據(jù)說(shuō)在大型項(xiàng)目的時(shí)候，可能會(huì)很慢。這個(gè)我還沒(méi)碰到過(guò)，因?yàn)闆](méi)有用到大型項(xiàng)目中。

下一篇，分享下 cmake 構(gòu)建 C++ 項(xiàng)目的一些語(yǔ)法和步驟。

cmake教程|cmake入門實(shí)戰(zhàn)

另外，文中涉及到的項(xiàng)目可以在我的github 找到。

Blog:

• rebootcat.com

• email: linuxcode2niki@gmail.com

2020-08-30 于杭州
By 史矛革

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