Why does Clang with libc in C 0x mode fail to link Boost::program_options examples?

Why can't clang with libc in c 0x mode link this boost::program_options example?

Background:

When attempting to compile and link a Boost::program_options example using Clang in C 0x mode with libc , the following error occurs:

Undefined symbols for architecture x86_64:
  // Various undefined symbols related to Boost::program_options

Explanation:

The primary reason for this error is that libc is not binary compatible with GCC's libstdc . Specifically:

• In libstdc , std::string is reference-counted.
• In libc , std::string uses "short string optimization" (SSO), which has different memory layout and behavior.

Solution:

To resolve this issue, you must rebuild Boost using Clang with libc as the standard library:

clang++ -stdlib=libc++ ...

Reason for Binary Incompatibility:

To prevent accidental mixing and runtime crashes due to binary incompatibility, libc leverages C 11's inline namespace feature to modify the ABI (Application Binary Interface) of std::string while maintaining the same API (Application Programming Interface). This ensures that the linker can differentiate between std::string from libstdc and std::string from libc .

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