Someone is writing C in C++ in libjson, and not declaring it correctly.

Can you please add

using namespace std;

to the top of  RJSONIO/src/libjson/Source/JSONChildren.h

to get memmove etc into scope.

The remaining problem,

"libjson/Source/NumberToString.h", line 130: Error: The function "snprintf" must have a prototype.

is trickier as snprintf is not a C++ and not a C90 function, and indeed the Solaris C++ headers seem to have vsnprintf but not snprintf. So that file needs to have

#ifdef __SUNPRO_CC
#include <stdio.h>
#else
#include <cstdio>
#endif