cmake的使用--目标的编译附源码

building simple targets

代码仓库地址

https://github.com/zzu-andrew/linux-sys/tree/dfew/CMake 

Executables

If an executable is defined with the EXCLUDE_FROM_ALL option, it will not be included in that default ALL target.

add_executable(targetName [WIN32] [MACOSX_BUNDLE]
	[EXCLUDE_FROM_ALL]
	source1 [source2 ...]
)

EXCLUDE_FROM_ALL设置之后将不再生成该可执行程序

Defining Libraries

add_library(targetName [STATIC | SHARED | MODULE]
    [EXCLUDE_FROM_ALL]
    source1 [source2 ...]
)

STATIC生成静态库

SHARED生成动态库

MODULE windows上的DLL

要是在add_library中省略了动态库还是静态库的选项，可以在调用cmake的时候通过编译选项指定如

cmake -DBUILD_SHARED_LIBS=YES /path/to/source

等价于在CMakeLists.txt中设置

set(BUILD_SHARED_LIBS YES)

Linking Targets

CMake captures this richer set of dependency relationships with its target_link_libraries() command, not just the simplistic idea of needing to link. The general form of the command is:

target_link_libraries(targetName
    <PRIVATE|PUBLIC|INTERFACE> item1 [item2 ...]
    [<PRIVATE|PUBLIC|INTERFACE> item3 [item4 ...]]
    ...
)

PRIVATE

Private dependencies specify that library A uses library B in its own internal implementation. Anything else that links to library A doesn’t need to know about B because it is an internal implementation detail of A.
PUBLIC

Public dependencies specify that not only does library A use library B internally, it also uses B in its interface. This means that A cannot be used without B, so anything that uses A will also have a direct dependency on B. An example of this would be a function defined in library A which has at least one parameter of a type defined and implemented in library B, so code cannot call the function from A without providing a parameter whose type comes from B.
INTERFACE

Interface dependencies specify that in order to use library A, parts of library B must also be 17used. This differs from a public dependency in that library A doesn’t require B internally, it only uses B in its interface. An example of where this is useful is when working with library targets defined using the INTERFACE form of add_library(), such as when using a target to represent a header-only library’s dependencies

target_link_libraries允许定义一个库是怎样依赖其他库，按照下面的顺序定义进行定义

add_library(collector src1.cpp)
add_library(algo src2.cpp)
add_library(engine src3.cpp)
add_library(ui src4.cpp)
add_executable(myApp main.cpp)
target_link_libraries(collector 
    PUBLIC ui
    PRIVATE algo engine
)
target_link_libraries(myApp PRIVATE collector)

In this example, the ui library is linked to the collector library as PUBLIC, so even though myApp only directly links to collector, myApp will also be linked to ui because of that PUBLIC relationship。

the targetName used with target_link_libraries() must have been defined by an add_executable() or add_library() command in the same directory from which target_link_libraries() is being called.

Linking Non-targets

target_link_libraries() command is more flexible than that. In addition to CMake targets, the following things can also be specified as items in a target_link_libraries() command:

Full path to a library file

CMake will add the library file to the linker command. If the library file changes, CMake will detect that change and re-link the target. prior 3.3 version (e.g. replace /usr/lib/libfoo.so with -lfoo)CMake会去查找库，带来的问题就是有大量历史缓存。

Plain library name

If just the name of the library is given with no path, the linker command will search for that library (e.g. foo becomes -lfoo or foo.lib, depending on the platform). This would be common for libraries provided by the system.

Link flag

As a special case, items starting with a hyphen other than -l or -framework will be treated as flags to be added to the linker command. Cmake手册中禁止这样使用，因为当是PUBLIC或者INTERFACE连接的时候这些命令可能会传递给其他的目标。

TIPS

目标名字和工程名字不必必须一样，当时通常教程和示例中会通过变量的形式将两者设置成一样的。

# Poor practice, but very common
set(projectName MyExample)
project(${projectName})
add_executable(${projectName} ...)

本章源码：

#This should be the first line of the CMakeLists.txt

cmake_minimum_required(VERSION 3.2)

# Poor practice, but very common
set(projectName MyProject)
project(${projectName} VERSION 4.7.2 LANGUAGES C)


add_library(collector src1.c)
add_library(echo_demo echo_demo.c)

#add_executable(targetName [WIN32] [MACOSX_BUNDLE]
#    [EXCLUDE_FROM_ALL]
#    source1 [source2 ...]
#)
# EXCLUDE_FROM_ALL 不对该可执行程序进行编译
set(executeProcess myExe)  # 使用变量
add_executable(${executeProcess} 
            main.c)

# PUBLIC 的链接方式可以直接在链接echo_demo的目标中使用 collector库中的函数
target_link_libraries(echo_demo
        PUBLIC collector)

target_link_libraries(${executeProcess}
    PRIVATE echo_demo        
)           

echo_demo.c

#include <stdio.h>

int echo_demo(void)
{
    printf("echo demo\n");


    return 0;
}

#include <stdio.h>

int echo_demo(void);

int main(int argc, char const *argv[])
{
    int ret = 0;
    ret = echo_demo();
    if(ret != 0)
    {
        printf("call echo demo failed\n");
    }

    return 0;
}

src1.c

#include <stdio.h>


void src1(void)
{
    printf("src1, is Linked.\n");
    return;
}