Object-C adopting C++ static lib (.a)

In order to adopt the C++ lib in Object-C project, I adopt [email protected]:ulwanski/md5.git as the base project, which is a md5 project in C++.

In this project, we are going to complete 2 tasks as following

• Compile a C++ static lib called libmd5.a.
• Create an Object-C project using md5 static lib built above.

The general idea is to expose the C interfaces which encapsulate the C++ static lib, since Object-C has no problem calling C functions directly.

##Purify C++ header to C header ###Move C++ relevated header to C++ source file

In original header file md5.h,

  #include <string>
  #include <cstring>

should be moved to file md5.cpp

###Refine C++ interfaces to C interfaces

In original header file md5.h,

  std::string md5(std::string dat);
  std::string md5(const void* dat, size_t len);
  std::string md5file(const char* filename);
  std::string md5file(std::FILE* file);
  std::string md5sum6(std::string dat);
  std::string md5sum6(const void* dat, size_t len);

should be changed into

  char* md5_C(char* dat);
  char* md5sum6_C(char* dat);
  char* md5file_C(const char* filename);

Reasons are

1.  There are actually only 3 functions necessary to be exposed, according to business logic.
2.  The interfaces should be in C syntax.

###Extern C interfaces In header file md5.h, it should declare that those interfaces should be linked as C functions. In this case, we braces the interfaces by

  #ifdef __cplusplus
  extern "C" {
  #endif

and

  #ifdef __cplusplus
  }
  #endif

##Add interface implementation in C++ source file In our case, we need to add three more functions in md5.cpp, which are

  char* md5_C(char* dat);
  char* md5sum6_C(char* dat);
  char* md5file_C(const char* filename);

They are used as a syntax adaptor from C++ to C.

##Usage

• Build up environment by ./envBuild.sh, under which Object-C project can be built in Linux.
• To build C and Object-C executable program mainC and mainObjC by make. The lib libmd5.a is generated in the folder lib within build process.
• Clean build by make clean.