C/C++构建工具库CMake

0x01 Why CMake?

在初学C语言时我们会了GCC基本编译命令：

gcc -o main main.c && chmod +x main
./main  # Hello World!

突然有了一个中型的小程序，大约有10个左右文件参与。于是转用Makefile定义每个文件之间的依赖：

CFLAGS=-static -Wall -g -I/usr/local/uriparser/include/uriparser -I./vendor/buffer/src
LDFLAGS=-L/usr/local/uriparser/lib -luriparser -L./vendor/buffer/build -lbuffer

SOURCES=$(wildcard src/**/*.c src/*.c)
OBJECTS=$(patsubst %.c,%.o,$(SOURCES))

TARGET=bin/http

all: $(TARGET)

$(TARGET): build $(OBJECTS)
	$(CC) $(LDFLAGS) -o $@ $(OBJECTS)

build:
	@mkdir -p bin

dev:CFLAGS+=-DNDEBUG
dev: all

clean:
	rm -rf bin/http src/*.o *.dSYM

再后来，程序越来越大。为了模块管理方便，以模块内Makefile为单位，想多模块协作。$(TARGET): build $(OBJECTS) $(CC) $(LDFLAGS) -o $@ $(OBJECTS)这些语句不再能够一句描述清楚各模块的关系。于是来到工程构建工具链最顶端CMake。

cmake_minimum_required(VERSION 3.5)

# Set the project name
project (protobuf_example)

# find the protobuf compiler and libraries
find_package(Protobuf REQUIRED)

# check if protobuf was found
if(PROTOBUF_FOUND)
    message ("protobuf found")
else()
    message (FATAL_ERROR "Cannot find Protobuf")
endif()

# Generate the .h and .cxx files
PROTOBUF_GENERATE_CPP(PROTO_SRCS PROTO_HDRS AddressBook.proto)

# Print path to generated files
message ("PROTO_SRCS = ${PROTO_SRCS}")
message ("PROTO_HDRS = ${PROTO_HDRS}")

# Add an executable
add_executable(protobuf_example
    main.cpp
    ${PROTO_SRCS}
    ${PROTO_HDRS})

target_include_directories(protobuf_example
    PUBLIC
    ${PROTOBUF_INCLUDE_DIRS}
    ${CMAKE_CURRENT_BINARY_DIR}
)

# link the exe against the libraries
target_link_libraries(protobuf_example
    PUBLIC
    ${PROTOBUF_LIBRARIES}
)

不说简单，但至少结构明了。这种简明的结构使得cmake地位和实际上VistualStudio的.sln一样，均具有以便捷成本构建大型程序的管理能力。

0x02 通用C/C++程序

cmake_minimum_required(VERSION 3.22)
project(clion)
set(CMAKE_CXX_STANDARD 11)

include_directories(include)

add_executable(clion main.cpp)

0x03 安卓Native

gradle指定CMakelist.txt文件位置，随后即可开始开发

// app.gradle
android {
    sourceSets {
        main {
            jniLibs.srcDirs = ['libs']
        }
    }
    externalNativeBuild {
        cmake {
            path "src/main/jni/CMakeLists.txt"
        }
    }

}

// CMakeLists.txt
cmake_minimum_required(VERSION 3.4.1)

include_directories(include)

add_library(mytest SHARED mytest.cpp)
target_link_libraries(mytest android log)


// 随后mytest.cpp和之前Android.mk体系一样正常开发即可