Memory Allocation concerns

 Memory allocation is probably the number one pitfall when writing
 Clipper 5.0 user defined functions in C.  This is due to the fact
 that with the introduction of Clipper 5.0, run-time memory allocation
 is accomplished via the Clipper VMM (Virtual Memory Manager.)1    In
 past versions of Clipper, when allocating memory from within C, the
 use of the Clipper Extend System memory allocation functions was
 recommended.  With the inclusion of VMM in Clipper 5.x memory
 allocation via the Clipper extend system it is an absolute must.  It
 is equally important to make absolutely sure that you free the memory
 you have allocated.

 Allocating memory with the Extend System

 The Extend System functions for memory allocation are _xalloc
 and _xgrab.  To allocate memory from C make a call to either
 _xalloc and _xgrab which returns a pointer if  successful.
 The difference between the two is the way they handle an
 error:  _xalloc  returns a  Null pointer to the C routine and
 _xgrab triggers a Clipper error.  Avoid C Library routines
 that allocate memory.  Many C Library functions automatically
 allocate  memory using the C library's memory allocation
 routines.  This automatic memory allocation must  be avoided.
 Care must be taken when using library routines from the
 following categories.2

 Memory Allocation routines

 Based on the statement that all memory must be allocated by
 the Clipper extend system,  is should be no surprise that C
 memory allocation routines can not be used.   This  includes
 alloca, calloc, malloc, along with their companion memory
 freeing functions.

 String manipulation routines

 Most string manipulation functions are passed both the source
 and target strings.   Because of this, string manipulation
 functions are generally quite easy to adapt to clipper use.
 Simply allocate the source and target buffers using an extend
 function, and pass them to the  string function as normal.

 Stream (buffered) I/O

 By default, Stream I/O routines (i.e.: fopen(), fclose(),
 fread(), fwrite(), ... ) automatically allocate  memory for a
 stream buffer.  They should be avoided, and the Low Level
 File I/O routines (i.e.:  open(), close(),  read(), write(),
 ... ) should be used instead.  Also, printf() (and scanf() )
 are  stream I/O routines and must be avoided.  Fortunately,
 cprintf() and sprintf() (along with cscanf() and sscanf())
 will work.  The following shows how to substitute these
 functions for printf():

 Instead of: printf( "Hello, world.\n"  )
        use: cprintf( "Hello, world.\r\n" )
             // uses raw mode - \n is CR only
         or: sprintf( stdout, "Hello, world.\n" )
             // stdout is defined in stdio.h