C and C++ : data file with error “Expected unquali

I would like to run C code in C++, using Xcode 8.33 on MacOS Sierra 10.12. I am new to C/C++, compilers, etc so please bear with me. The C code, when compiled and ran with make via Terminal, works. But when I throw all the same files into a XCode C++ project, there is an error with the data file. Note: I did change main.c to main.cpp.

//**** main.cpp *****

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <limits.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <ctype.h>

extern "C" {
#include "msclib.h"
}

int main(int argc, char** argv)
{
    assert(argc >= 1);
    return msc_get_no(argv[1]);

}

The file msclib.c calls on the data file mscmix_dat.c. Here is also msclib.h

// ***** msclib.h *****

extern size_t msc_get_no(const char*); 

// ***** msclib.c *****

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <string.h>
#include <ctype.h>

#include "msclib.h"

struct msc_data
{
   const char* code;
   const char* desc;
};

typedef struct msc_data MSCDat;

static const MSCDat mscdat[] =
#include "mscmix_dat.c"
   ;

static const size_t msccnt = sizeof(mscdat) / sizeof(mscdat[0]);

static int msc_cmp(const void* a, const void* b)
{
   const char*   msc_code = a;
   const MSCDat* p        = b;   
   return strcmp(msc_code, p->code);
}

size_t msc_get_no(const char* msc_code)
{
   assert(NULL != msc_code);
   assert(strlen(msc_code) == 5);

   MSCDat* p = bsearch(msc_code, &mscdat[0], msccnt, sizeof(mscdat[0]), msc_cmp);

   if (NULL == p)
   {
      fprintf(stderr, "MSC \"%s\" not valid\n", msc_code);
      return 0;
   }

   assert(NULL != p);
   return p - &mscdat[0];
}

When running/compiling, the mscmix_dat.c file gets the error Expected identifier or ( - which is what I need help with. Even when I replace mscmix_dat.c with .cpp, I get the error Expected unqualified-id

// ***** mscmix_dat.c *****
{ //<-- Xcode highlights this line and gives the error
   { "*****", "Error" },
   { "00-01", "Instructional exposition (textbooks, tutorial papers, etc.)" },
   { "00-02", "Research exposition (monographs, survey articles)" },
   { "00A05", "General mathematics" },
   .
   .
   .
}

I would appreciate explanations as to why this error is occurring, suggestions on how to fix it, and if necessary alternatives to processing this data file. Thank you!

OP here. These are the steps I took to resolve my issue, based on the last edit of my question:

With the separate files, as given in my question, the error was Expected identifier in mscmix_dat.c.
Per @LightnessRacesinOrbit's suggestion, I consolidated the multiple main.cpp, msclib.h, msclib.c, and mscmix_dat.c files into two files: main.cpp and msclib.c, by replacing the #include thisfile.c with the actual file code content. I also changed msclib.c to .cpp via simple rename. This eliminated the original error of Expected identifier, but a new one arose.
Compiling the two files gave multiple errors in msclib.cpp, all wrt variable type conversions.
Because of C++ differences from C, I handled the type conversion issue via casting, but also respecting const.

Below is my final, successfully compiling code.

// **** main.cpp ****
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <limits.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <ctype.h>

#include<string>
#include<iostream>
using namespace std;

extern size_t msc_get_no(const char*);

int main(int argc, char** argv)
{
    assert(argc >= 0);
    return (int)msc_get_no(argv[1]); // casting

}

// **** msclib.cpp ****
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <string.h>
#include <ctype.h>

extern size_t msc_get_no(const char*);

struct msc_data
{
   const char* code;
   const char* desc;
};

typedef struct msc_data MSCDat;

static const MSCDat mscdat[] =
{
    { "*****", "Error" },
    { "00-01", "Instructional exposition (textbooks, tutorial papers, etc.)" },
    { "00-02", "Research exposition (monographs, survey articles)" },
    { "00A05", "General mathematics" }
}
   ;

static const size_t msccnt = sizeof(mscdat) / sizeof(mscdat[0]);

static int msc_cmp(const void* a, const void* b)
{
   const char*   msc_code = static_cast<const char*>(a); //<----
   const MSCDat* p        = static_cast<const MSCDat*>(b); // (const MSCDat*)b also works
   return strcmp(msc_code, p->code);
}


size_t msc_get_no(const char* msc_code)
{
   assert(NULL != msc_code);
   assert(strlen(msc_code) == 5);

    MSCDat* p; // changed initialization of p
   p = (MSCDat*) bsearch(msc_code, &mscdat[0], msccnt, sizeof(mscdat[0]), msc_cmp);

   if (NULL == p)
   {
      fprintf(stderr, "MSC \"%s\" not valid\n", msc_code);
      return 0;
   }

   assert(NULL != p);
   return p - &mscdat[0];
}