Undefined symbols for architecture x86_64 in Xcode 8.3.3 for iOS app

Question

I have just created a new project in Xcode 8.3.3 with Swift for iOS and I tried importing the external library SwiftLibModbus

I have ported the library to use Swift 3 (meaning, I fixed all the errors). This library is using another library named libmodbus that is written in C and I am getting an Undefined symbols for architecture x86_64 error when this library is imported.

Here is the full error:

Undefined symbols for architecture x86_64:
  "_modbus_free", referenced from:
      __TFC23SomeProject_Wi_Fi_Connect14SwiftLibModbusD in SwiftLibModbus.o
  "_modbus_strerror", referenced from:
      __TFC23SomeProject_Wi_Fi_Connect14SwiftLibModbusP33_56F751289226F31D555D5DEEC0F0514F12buildNSErrorfT5errnoVs5Int32_CSo7NSError in SwiftLibModbus.o
  "_modbus_write_registers", referenced from:
      __TFFC23SomeProject_Wi_Fi_Connect14SwiftLibModbus23writeRegistersFromAndOnFT7addressVs5Int3211numberArrayCSo7NSArray7successFT_T_7failureFCSo7NSErrorT__T_U_FT_T_ in SwiftLibModbus.o
  "_modbus_read_input_registers", referenced from:
      __TFFC23SomeProject_Wi_Fi_Connect14SwiftLibModbus22readInputRegistersFromFT12startAddressVs5Int325countS1_7successFGSaPs9AnyObject__T_7failureFCSo7NSErrorT__T_U_FT_T_ in SwiftLibModbus.o
  "_modbus_write_register", referenced from:
      __TFFC23SomeProject_Wi_Fi_Connect14SwiftLibModbus13writeRegisterFT7addressVs5Int325valueS1_7successFT_T_7failureFCSo7NSErrorT__T_U_FT_T_ in SwiftLibModbus.o
  "_modbus_write_bit", referenced from:
      __TFFC23SomeProject_Wi_Fi_Connect14SwiftLibModbus8writeBitFT7addressVs5Int326statusSb7successFT_T_7failureFCSo7NSErrorT__T_U_FT_T_ in SwiftLibModbus.o
  "_modbus_new_tcp", referenced from:
      __TFC23SomeProject_Wi_Fi_Connect14SwiftLibModbus8setupTCPfT9ipAddressCSo8NSString4portVs5Int326deviceS2__Sb in SwiftLibModbus.o
  "_modbus_set_error_recovery", referenced from:
      __TFC23SomeProject_Wi_Fi_Connect14SwiftLibModbus8setupTCPfT9ipAddressCSo8NSString4portVs5Int326deviceS2__Sb in SwiftLibModbus.o
  "_modbus_close", referenced from:
      __TFC23SomeProject_Wi_Fi_Connect14SwiftLibModbus10disconnectfT_T_ in SwiftLibModbus.o
  "_modbus_connect", referenced from:
      __TFC23SomeProject_Wi_Fi_Connect14SwiftLibModbus16connectWithErrorfCSo7NSErrorSb in SwiftLibModbus.o
      __TFFC23SomeProject_Wi_Fi_Connect14SwiftLibModbus7connectFT7successFT_T_7failureFCSo7NSErrorT__T_U_FT_T_ in SwiftLibModbus.o
  "_modbus_read_registers", referenced from:
      __TFFC23SomeProject_Wi_Fi_Connect14SwiftLibModbus17readRegistersFromFT12startAddressVs5Int325countS1_7successFGSaPs9AnyObject__T_7failureFCSo7NSErrorT__T_U_FT_T_ in SwiftLibModbus.o
  "_modbus_read_input_bits", referenced from:
      __TFFC23SomeProject_Wi_Fi_Connect14SwiftLibModbus17readInputBitsFromFT12startAddressVs5Int325countS1_7successFGSaPs9AnyObject__T_7failureFCSo7NSErrorT__T_U_FT_T_ in SwiftLibModbus.o
  "_modbus_read_bits", referenced from:
      __TFFC23SomeProject_Wi_Fi_Connect14SwiftLibModbus12readBitsFromFT12startAddressVs5Int325countS1_7successFGSaPs9AnyObject__T_7failureFCSo7NSErrorT__T_U_FT_T_ in SwiftLibModbus.o
  "_modbus_set_slave", referenced from:
      __TFC23SomeProject_Wi_Fi_Connect14SwiftLibModbus8setupTCPfT9ipAddressCSo8NSString4portVs5Int326deviceS2__Sb in SwiftLibModbus.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Is there any way around this? This is actually the only library I have found available for Modbus.

Thanks :)

Answer 1

Hmmm... Did you drag the files inside a folder using "Copy items if needed" and "Create folder references" marked?

If so, Xcode might not understand it needs to compile the files for the right architecture inside that folder. Just drag the bunch of files directly to Xcode and it should be fine.

Answer 2

If you just drag all files to XCode, it builds C code for currently selected architecture, you may need to clean and build project to get library compiled for right architecture after changing target (device/simulator)

To avoid this, native libraries should be built with external script for all required architectures and merged in one "fat" or "universal" library.

Answer 3

check whether you have import your framework like

@import framework;

Answer 4

If the library that gives these errors has a ".a" file, then you need to check that this file is added to Build Phases/Link Binary With Libraries.

Answer 5

Mybe you had draged two library which is same to project, Xcode is confused about which one to use.just delete one,it will be ok.

Answer 6

As pointed out somewhere else on SO, I've solved this one by:

• renaming my projects and target which had an _ (underscore) in the name
• rebuilding the pod with pod update
• cleaning derived data File -> Workspace Settings -> Grey Arrow -> CMD + delete
• closing and reopening workspace
• creating a new test target from the <-> target menu