Undefined symbols for architecture x86_64: in mac OS

1、我当前使用的mac OS系统版本：

  macOS Mojave

Version 10.14.6

2、Command Line Tools：

Xcode Version 11.3.1 (11C504)

3、问题如下：

Showing All Errors Only

Ld /Users/***/Library/Developer/Xcode/DerivedData/UseQueue-dcwulpumiqqtwjgycwqbsluancwo/Build/Products/Debug/UseQueue normal x86_64 (in target 'UseNet' from project 'UseNet')

Undefined symbols for architecture x86_64:

  "_pcre2_code_free_8", referenced from:

      _ngx_regex_cleanup in ngx_regex.o

  "_pcre2_compile_8", referenced from:

      _ngx_regex_compile in ngx_regex.o

  "_pcre2_compile_context_create_8", referenced from:

      _ngx_regex_compile in ngx_regex.o

  "_pcre2_compile_context_free_8", referenced from:

      _ngx_regex_cleanup in ngx_regex.o

  "_pcre2_config_8", referenced from:

      _ngx_regex_pcre_jit in ngx_regex.o

  "_pcre2_general_context_create_8", referenced from:

      _ngx_regex_compile in ngx_regex.o

  "_pcre2_general_context_free_8", referenced from:

      _ngx_regex_compile in ngx_regex.o

  "_pcre2_get_error_message_8", referenced from:

      _ngx_regex_compile in ngx_regex.o

  "_pcre2_get_ovector_count_8", referenced from:

      _ngx_regex_exec in ngx_regex.o

  "_pcre2_get_ovector_pointer_8", referenced from:

      _ngx_regex_exec in ngx_regex.o

  "_pcre2_jit_compile_8", referenced from:

      _ngx_regex_module_init in ngx_regex.o

  "_pcre2_match_8", referenced from:

      _ngx_regex_exec in ngx_regex.o

  "_pcre2_match_data_create_8", referenced from:

      _ngx_regex_exec in ngx_regex.o

  "_pcre2_match_data_free_8", referenced from:

      _ngx_regex_exec in ngx_regex.o

      _ngx_regex_cleanup in ngx_regex.o

  "_pcre2_pattern_info_8", referenced from:

      _ngx_regex_compile in ngx_regex.o

ld: symbol(s) not found for architecture x86_64

clang: error: linker command failed with exit code 1 (use -v to see invocation)

其实，不管在什么系统环境下，针对此问题的解决是类似的。从报的错误来看，很明显，是在当前的开发程序中无法访问到对应函数的实现，也就是说有函数声明，却找不到函数体。明白了原因，解决就简单了。

解决方式：

        直接引入pcre2相应版本的静态库。

        为什么需要引入呢？原因，程序编译连接时，在默认搜索目录下没有找到对应的函数实现（相应的库）。此依赖软件，是我个人使用port自行安装的，没有在系统lib下。

        找到/opt/local/lib，将对应的库拖拽添加到开发环境中，如图，

 问题解决。