build/Objects-normal/i386/fmdb.o

添加FMDB类库时候引起的linker command failed with exit code 1 (use -v to see invocation)错误

duplicate symbol _main in:
    /Users/Nyist-MacBook/Library/Developer/Xcode/DerivedData/iMessage-diqacvooqxpakffoxkdntcziummf/Build/Intermediates/iMessage.build/Debug-iphonesimulator/iMessage.build/Objects-normal/i386/fmdb.o
    /Users/Nyist-MacBook/Library/Developer/Xcode/DerivedData/iMessage-diqacvooqxpakffoxkdntcziummf/Build/Intermediates/iMessage.build/Debug-iphonesimulator/iMessage.build/Objects-normal/i386/main.o
ld: 1 duplicate symbol for architecture i386
clang: error: linker command failed with exit code 1 (use -v to see invocation)

编译时检测到两个入口函数，也就是两个main函数，需要删除一个；

因为从github上下载下来的FMDB库文件中有个fmdb.m(Demo文件)没留意，造成这样错误。

移除FMDB 文件夹里的fmdb.m文件即可；

其实类似linker command failed with exit code 1 (use -v to see invocation)错误原因有很多，注意看提示信息。