//myAPI.h
int ADD(int a, int b);
int MINUS(int a, int b);

//myAPI.cpp
#include "myAPI.h"int ADD(int a, int b){return a + b;
}int MINUS(int a, int b){return a - b;
}

//main.cpp
#include "myAPI.h"
#include <iostream>int main(){std::cout << "1 + 1 = " << ADD(1, 1) << std::endl;std::cout << "1 - 1 = " << MINUS(1, 1) << std::endl;return 0;
}

all: main-1 main-2 main-a main-so main-so2main-1: myAPI.cpp main.cpp myAPI.hg++ -o main-1 myAPI.cpp main.cpp@echo "main-1 done.  直接编译省略显示编译.o文件"@echomain-2: main.cpp myAPI.og++ -o main-2 myAPI.o main.cpp@echo "main-2 done.  显示编译.o文件"@echomain-a: libmyAPI.ag++ -o main-a  main.cpp libmyAPI.a@echo "main-a done.  使用.a静态库文件 链接生成程序"@echomain-so: libmyAPI.sog++ -o main-so main.cpp ./libmyAPI.so@echo "main-so done.  直接使用.so动态库文件(需要带路径,运行时直接使用此路径) 链接生成程序"@echomain-so2: libmyAPI.sog++ -o main-so2 main.cpp -L. -lmyAPI@echo "main-so2 done.  让g++自动在当前目录("."表示当前目录,或"./")查找.so动态库文件 链接生成程序"@echo "    但运行时默认到/usr/lib目录查找,,或运行前设置环境变量 LD_LIBRARY_PATH 为动态库的路径"@echomyAPI.o: myAPI.cpp myAPI.hg++ -c myAPI.cpp@echo "myAPI.o done.  编译.o文件"@echolibmyAPI.a: myAPI.oar crv libmyAPI.a myAPI.o@echo "libmyAPI.a done.  编译.a静态库文件"@echolibmyAPI.so:g++ -fPIC -c myAPI.cppg++ -shared -o libmyAPI.so myAPI.o@echo "libmyAPI.so done.  编译.so动态库文件,需要 .o文件编译时加选项 -fPIC"@echo "    或者 直接编译动态库:"@echo "    g++ -shared -fPIC -o libmyAPI.so myAPI.cpp"@echo#或者 直接编译动态库:
#libmyAPI.so:
#    g++ -shared -fPIC -o libmyAPI.so myAPI.cpp
#clean:rm -f *.o *.a *.so main-*

[root@lzp test2]# ./main-1
1 + 1 = 2
1 - 1 = 0
[root@lzp test2]# ./main-2
1 + 1 = 2
1 - 1 = 0
[root@lzp test2]# ./main-a
1 + 1 = 2
1 - 1 = 0
[root@lzp test2]# ./main-so
1 + 1 = 2
1 - 1 = 0
[root@lzp test2]# ./main-so2
./main-so2: error while loading shared libraries: libmyAPI.so: cannot open shared object file: No such file or directory

[root@lzp test2]# LD_LIBRARY_PATH=./
[root@lzp test2]# ./main-so2
./main-so2: error while loading shared libraries: libmyAPI.so: cannot open shared object file: No such file or directory
[root@lzp test2]# LD_LIBRARY_PATH=./  ./main-so2
1 + 1 = 2
1 - 1 = 0

例如:

g++ ...  obj($?) -l(上层逻辑lib) -l(中间封装lib) -l(基础lib) -l(系统lib)  -o $@

这样写可以避免很多问题，这个是在搭建项目的构建环境的过程中需要考虑 清楚地，在编译和链接上浪费太多的生命不值得！