BUILD.gn文件怎么写，Gn + Ninja编译一个Hello world程序的例子Demo

• Ninja安装流程见：一个能直接运行的Ninja例子，build.ninja文件怎么写？
• Gn安装流程见：Ubuntu18.04下安装Gn软件

• 这是一个简单的BUILD.gn配置文件

jim@ubuntu:~/0_Git/third_party_gn/examples/simple_build$ cat BUILD.gn 
# Copyright 2014 The Chromium Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

executable("hello") {
  sources = [ "hello.cc" ]

  deps = [
    ":hello_shared",
    ":hello_static",
  ]
}

shared_library("hello_shared") {
  sources = [
    "hello_shared.cc",
    "hello_shared.h",
  ]

  defines = [ "HELLO_SHARED_IMPLEMENTATION" ]
}

static_library("hello_static") {
  sources = [
    "hello_static.cc",
    "hello_static.h",
  ]
}

• 这是Gn官方的例子，在Gn的源码里面

  • 使用Ubuntu系统，安装Git、Ninja、Gn、Clang软件
  • git clone git@gitee.com:openharmony/third_party_gn.git 拉取源码，或者：
  • https://gitee.com/openharmony/third_party_gn/repository/archive/master.zip 下载源码

• cd examples/simple_build/ 下载源码后进入其中的子目录

• ls 先看看里面的文件

jim@ubuntu:~/0_Git/third_party_gn/examples/simple_build$ ls
build  BUILD.gn  hello.cc  hello_shared.cc  hello_shared.h  hello_static.cc  hello_static.h  README.md  tutorial

jim@ubuntu:~/0_Git/third_party_gn/examples/simple_build$ cat hello.cc
// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <stdio.h>

#include "hello_shared.h"
#include "hello_static.h"

int main(int argc, char* argv[]) {
  printf("%s, %s\n", GetStaticText(), GetSharedText());
  return 0;
}

• gn gen -C out 按Gn规则文件生成Ninja配置文件

jim@ubuntu:~/0_Git/third_party_gn/examples/simple_build$ gn gen -C out
Done. Made 3 targets from 4 files in 45ms

• cd out/ 进入输出目录，看看生成的什么内容

jim@ubuntu:~/0_Git/third_party_gn/examples/simple_build$ tree out/
out/
├── args.gn
├── build.ninja
├── build.ninja.d
├── obj
│   ├── hello.ninja
│   ├── hello_shared.ninja
│   └── hello_static.ninja
└── toolchain.ninja

1 directory, 7 files


jim@ubuntu:~/0_Git/third_party_gn/examples/simple_build$ cat out/build.ninja
ninja_required_version = 1.7.2

rule gn
  command = ../../../../../../../usr/bin/gn --root=./.. -q --C --regeneration gen .
  pool = console
  description = Regenerating ninja files

build build.ninja: gn
  generator = 1
  depfile = build.ninja.d

subninja toolchain.ninja

build hello_shared: phony ./libhello_shared.so
build hello_static: phony obj/libhello_static.a
build $:hello: phony hello
build $:hello_shared: phony ./libhello_shared.so
build $:hello_static: phony obj/libhello_static.a

build all: phony $
    hello $
    ./libhello_shared.so $
    obj/libhello_static.a

default all

• ninja 开始编译（和make命令类似）

jim@ubuntu:~/0_Git/third_party_gn/examples/simple_build/out$ ninja
[6/6] LINK hello

jim@ubuntu:~/0_Git/third_party_gn/examples/simple_build/out$ tree
.
├── args.gn
├── build.ninja
├── build.ninja.d
├── hello
├── libhello_shared.so
├── obj
│   ├── hello.hello.o
│   ├── hello.ninja
│   ├── hello_shared.ninja
│   ├── hello_static.ninja
│   ├── libhello_shared.hello_shared.o
│   ├── libhello_static.a
│   └── libhello_static.hello_static.o
└── toolchain.ninja

1 directory, 13 files

• ./hello 运行编译后的可执行文件

jim@ubuntu:~/0_Git/third_party_gn/examples/simple_build/out$ ./hello 
Hello, world

• 参考网址：
  • GN环境搭建