Differences between several flags in dlopen: rtld_lazy rtld_now rtld_global

Void * dlopen (const char * filename, int flag );

Flag: rtld_lazy rtld_now rtld_global, which has the following meanings:

Rtld_lazy: Before dlopen returns, do not parse undefined variables (such as the external variable extern or function) in the dynamic library, that is, do not parse the address of the variable.

Rtld_now: different from above, he needs to parse the address of each undefined variable before dlopen returns. If the address cannot be parsed, the return value is null in dlopen. The error is:

: Undefined Symbol: XXXX .......

Rtld_global: it means that the definition variables parsed in the library can be used in other subsequent linked libraries.