When run examples/ch2.1/hello-03/main.go , an error occurred

[cag2050]

Description of problem

when run https://github.com/chai2010/advanced-go-programming-book/blob/master/examples/ch2.1/hello-03/main.go, an error occurred：

GOROOT=/usr/local/go #gosetup
GOPATH=/Users/cag2050/go #gosetup
/usr/local/go/bin/go build -o /private/var/folders/bs/c1rv5w6n0cn77fp62sj3hzhh0000gp/T/GoLand/___5go_build_main_go /Users/cag2050/Documents/GoLandProjects/advanced-go-programming-book/examples/ch2.1/hello-03/main.go #gosetup
# command-line-arguments
Undefined symbols for architecture x86_64:
  "_SayHello", referenced from:
      __cgo_42939a32e160_Cfunc_SayHello in _x002.o
     (maybe you meant: __cgo_42939a32e160_Cfunc_SayHello)
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Expected result

do not have error

Actual result

Further information