DEV C++ main文件不能编译 但是点中构造函数的头文件和函数实现文件却可以编译

项目共有3个文件 main.cpp LongNum.cpp LongNum.h

选中LongNum.cpp LongNum.h点击编译按钮可以完成编译

如图

点选中main.c编译的时候就会出现错误

如图

具体的错误信息是：

- C++ 编译器: C:\Program Files (x86)\Dev-Cpp\MinGW64\bin\g++.exe
- 命令: g++.exe "D:\c\main.cpp" -o "D:\c\main.exe"  -I"C:\Program Files (x86)\Dev-Cpp\MinGW64\include" -I"C:\Program Files (x86)\Dev-Cpp\MinGW64\x86_64-w64-mingw32\include" -I"C:\Program Files (x86)\Dev-Cpp\MinGW64\lib\gcc\x86_64-w64-mingw32\4.9.2\include" -I"C:\Program Files (x86)\Dev-Cpp\MinGW64\lib\gcc\x86_64-w64-mingw32\4.9.2\include\c++" -L"C:\Program Files (x86)\Dev-Cpp\MinGW64\lib" -L"C:\Program Files (x86)\Dev-Cpp\MinGW64\x86_64-w64-mingw32\lib" -static-libgcc -lobjc
C:/Program Files (x86)/Dev-Cpp/MinGW64/bin/../lib/gcc/x86_64-w64-mingw32/4.9.2/../../../../x86_64-w64-mingw32/bin/ld.exe: cannot find -lobjc
collect2.exe: error: ld returned 1 exit status

大概意思是.o文件丢失。那么为什 选中两位两个文件就可以编译呢？