搞定了。需要通过两步去编译，多谢多谢。
https://www.sfml-dev.org/tutorials/2.5/start-linux.php

1.

g++ -c main.cpp -I<sfml-install-path>/include

2.

g++ main.o -o sfml-app -L<sfml-install-path>/lib -lsfml-graphics -lsfml-window -lsfml-system

3. ./sfml-app


==================================================================================
我要用的第三方库是SFML，目录结构如下：
> tree -L 2
.
├── SFML
│   ├── Frameworks
│   ├── changelog.md
│   ├── doc
│   ├── examples
│   ├── extlibs
│   ├── include
│   ├── lib
│   ├── license.md
│   ├── readme.md
│   └── templates
├── hello.cpp
├── hello.dSYM
│   └── Contents
├── helloworld.cpp
├── helloworld.dSYM
│   └── Contents
├── images
│   ├── background.png
│   ├── frame.png
│   └── tiles.png
└── main.cpp

--------------------------------------------------------------
main.cpp部分代码:

#include <SFML/Graphics.hpp>
#include <time.h>

using namespace sf;

---------------------------------------------------------------
环境： MacOS, Clang

> clang --version
Apple LLVM version 10.0.1 (clang-1001.0.46.4)
Target: x86_64-apple-darwin18.7.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin


---------------------------------------------------------------
遇到困难, SFML这个库找不到：
fatal error: 'SFML/Graphics.hpp' file not found
#include <SFML/Graphics.hpp>
         ^~~~~~~~~~~~~~~~~~~
--
修改:qwersex FROM 98.126.155.*
FROM 120.229.88.*

谢谢sand，添加了还是不行。另外，我在tasks.json中还添加了5项，可以编译部分，但是最后还是提示错误，是不是我还需要补充一些？
--------------------------------------------------------------------------
错误提示
----------------------
ld: library not found for -libsfml-graphics
clang: error: linker command failed with exit code 1 (use -v to see invocation)
The terminal process terminated with exit code: 1


--------------------------------------------------------------------------
c_cpp_properties.json
----------------------
{
    "configurations": [
        {
            "name": "Mac",
            "includePath": [
                "SFML/include",
                "${workspaceFolder}/**"
            ],
            "defines": [],
            "macFrameworkPath": [
                "/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/System/Library/Frameworks"
            ],
            "compilerPath": "/usr/bin/clang",
            "cStandard": "c11",
            "cppStandard": "c++17",
            "intelliSenseMode": "clang-x64"
        }
    ],
    "version": 4
}

--------------------------------------------------------------------------
task.json
----------------------
            "args": [
                "-std=c++17",
                "-stdlib=libc++",
                "-g",
                "${file}",
                "-o",
                "${fileDirname}/${fileBasenameNoExtension}",
                "-I",            //添加的
                "SFML/include",  //添加的
                "-L",            //添加的
                "SFML/lib",      //添加的
                "-libsfml-graphics",   //添加的
            ],
【 在 freesand 的大作中提到: 】
: VSCode 配置中添加 C_Cpp.default.includePath 为路径列表
--
FROM 98.126.155.*