VX/C – OpenVMS C to ANSI C

Processing model

Run lifecycle

1. Install a watchdog timer and exit handlers to bound each run.
2. Read trace controls from the environment (VXCPP_DEBUG / VXCPP_TRACE).
3. Parse the command-line switches.
4. Load the target platform personality (Linux or macOS) predefined macros; if none is selected, abort.
5. Parse the source, applying edits into the edit buffer.
6. If any parse errors occurred, suppress output and abort; otherwise write the transformed source to --output= or standard output.

Components

VMS-C constructs handled

The extensions and non-ANSI constructs VX/C rewrites into portable form include:

Target personalities

VX/C selects a target personality at run time and loads that host's predefined macros so preprocessor conditionals resolve the same way the native compiler would. Two personalities ship today: Linux, using GCC predefined macros, and macOS, using Apple LLVM/clang predefined macros. If no personality is selected, VX/C aborts rather than guessing.

Example: missing return type and terminal return

An old-style function with no return type and no return statement is legal in VMS C but not in ANSI C. VX/C inserts int and a terminating return.

/* VMS / OpenVMS C */
static ACCT_INIT (void)
{
}

/* Migrated ANSI C */
static int /*S7-100*/ ACCT_INIT (void)
{
    return ( int)0; /*S7-102*/
}

Example: missing arguments to a VMS system service

VX/C pads system-service calls (SYS$, LIB$, STR$, and similar) that were written with fewer than the required arguments.

/* VMS / OpenVMS C */
int t = SYS$QIO(0);

/* Migrated ANSI C */
int t = SYS$QIO(0/*S7-041*/,0,0,0,0,0,0,0,0,0,0,0);

Example: buffered I/O retargeting and argument padding

Buffered-I/O calls are retargeted to the vms_* runtime wrappers (S7-040), short argument lists are padded (S7-041), and fopen gets a trailing NULL (S7-042).

/* VMS / OpenVMS C */
cp = strerror(12);
fp = fopen("account.dat", "r+", "shr=nil");
i  = fclose(fp);

/* Migrated ANSI C */
cp = /*S7-040*/vms_strerror(12/*S7-041*/,0);
fp = /*S7-040*/vms_fopen("account.dat", "r+", "shr=nil", NULL /*S7-042*/);
i  = /*S7-040*/vms_fclose(fp);

Example: address-of-constant rewrites

Taking the address of a numeric constant, a float, or a string literal is rewritten to a portable equivalent.

/* VMS / OpenVMS C */
i  = & 1234;
i  = & 133.23;
cp = &"HELLO";

/* Migrated ANSI C */
i  = i_constant(1234)/*S7-008*/;
i  = f_constant(133.23)/*S7-010*/;
cp = "HELLO"/*S7-012*/;

Example: K&R varargs to stdarg

Old K&R variadic prototypes are converted to <stdarg.h> form: #include <varargs.h> becomes #include <stdarg.h>, the va_alist / va_dcl parameter list is rewritten with a generated argument counter, and va_start / va_count are adjusted to match. The vxaddargs companion tool supplies the correct fixed argument count for each function through the --vararg_file database.

Core switches

Configuration and mapping files

Common option sets and header remaps do not have to be retyped on every run. --hmapfile= reads input-header to output-header mappings, --vararg_file= supplies fixed argument counts for variadic functions, and --copy= processes a whole directory tree, mirroring its subdirectories into an output tree. This makes VX/C easy to drive from a batch script over a source estate and then compile the transformed output.

Trace controls

Tracing is available through the -t switch or the VXCPP_DEBUG / VXCPP_TRACE environment variables, which accept a comma-separated option string (pre-processor, tokens, symbols, files, macros, and more) plus an optional output=<file> redirect. YYDEBUG=n enables parser debug output.

#include fixes

Built-in VMS to POSIX header map

Beyond user-supplied --hmap* maps, VX/C ships a fixed VMS to POSIX header-name table. The built-in pairs are:

Example: #pragma dictionary to #include

Migrated code that pulled records from the OpenVMS Common Data Dictionary through #pragma dictionary is rewritten to a portable #include of the dictionary-derived header.

/* VMS / OpenVMS C */
typedef
#pragma dictionary "account_cmn.def"

/* Migrated ANSI C */
typedef
#include "account_cmn.def.h" /*S7-084 DICTIONARY */

Diagnostics and exit codes

All operator messages are written to standard error; transformed source goes to --output= or standard output. VX/C returns a distinct exit code per failure class so a build script can react appropriately.

Invocation

vxcpp [switches] file.c        # transformed source to stdout or --output=
vxcpp --copy=<in>,<out> ...     # directory-tree mode

Core switches

Environment variables

Exit codes

At a glance

• Binary: vxcpp (product VX/C).
• Input: OpenVMS/VAX-C and DEC C, including VMS-C extensions.
• Output: portable, POSIX-compliant ANSI C.
• Change markers: inline /*S7-nnn*/ tags across 14 feature-coded categories.
• Header remaps: 29 built-in VMS to POSIX pairs, plus user --hmap* maps.
• Targets: Linux and other POSIX/UNIX platforms (e.g. macOS). No Windows.