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HP C
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In HP C, if the argument of the unary & operator is an array, the result now has the type "pointer to array". Previously, in VAX C, the result would have the type "pointer to the element type of the array".
HP C supports the new standard C operator, unary plus (+). This operator returns the value of its operand (possibly widened by the integral promotions).
As required by standard C, HP C issues a warning (in all modes except VAX C mode) to diagnose a constraint violation if one of the operands of a relational operator is a pointer to a function. For example, the following code would issue a warning:
int (*f)(); if (f > NULL) |
Note that it is valid to use the equality operators to compare function pointers.
Standard C has tighter assignment compatibility rules than those previously enforced by VAX C. (Note that assignment compatibility rules also control function argument passing.) HP C assignment compatibility differs from that of VAX C in the following ways:
Function prototype support, the new const and volatile type qualifiers, and the void type, were already implemented in VAX C. The following sections describe the additional HP C support that affects declarations. References are to the relevant sections in the C Standard.
The C Standard requires that an implementation support certain minimum requirements; these are listed in the referenced section. In those cases where VAX C imposes a fixed limit, that limit has always met or exceeded the Standard's requirements, and programs that exceed any of these limits elicit the appropriate errors. In strict ANSI C mode, HP C now issues diagnostics against any source program constructs that exceed any of the Standard limits as well.
In strict ANSI C mode, HP C now issues diagnostic messages against declarations of external names in excess of six characters, or external names that are intended to denote different objects but that have the same spelling, and ignores alphabetical case.
The C Standard invalidates empty declarations, except for two special cases: one involving structure/union tags and the other involving the enumeration type. In strict ANSI C mode, HP C issues an error message against any declaration that does not declare at least one of the following: a declarator, a tag, or the members of an enumeration.
The C Standard specifies that allowing the placement of any storage-class specifier other than at the beginning of a declaration is an obsolete feature. In strict ANSI C mode, HP C now issues an informational diagnostic to that effect when appropriate.
The C Standard specifies that old-style function declarations and definitions (that is, those not using the function prototype format) are obsolete. Old-style function declarations and definitions cause an informational message to be issued in all modes except VAX C.
The C Standard restricts the form of the declarator in a function definition: the function type itself may not be inherited from a typedef-name; that is, the declarator must explicitly contain a (possibly empty) parenthesized parameter list. If not, HP C in strict ANSI C mode issues an error message.
HP C for OpenVMS Systems supports the initialization of unions.
In VAX C, an aggregate initializer consisting of a single item does not have to have the outer braces. The outer braces are required by the C Standard.
HP C allows this case in VAX C mode.
The HP C compiler initializes bit-field structure members differently than VAX C does. See Section 4.7.2.
The following sections describe the differences between the VAX C and the HP C preprocessors. Most of these differences reflect the HP C preprocessor's conformance to the C Standard. References are to the relevant sections in the C Standard.
Note that most VAX C-specific preprocessor extensions are unaffected by these changes. These extensions continue to be supported quietly in VAX C mode, but elicit appropriate diagnostics in strict ANSI C mode.
The C Standard removes the VAX C restriction that requires the # character introducing a preprocessor directive to always appear in column 1 of the source line. In HP C, white space and comments can now precede the # on the same line.
Before the C Standard, the lack of a precise definition of the behavior of macro expansion led to a number of inconsistencies among different C implementations. HP C, in adhering to the C Standard, removes these and many other discrepancies by specifying precisely how macro substitution is to be performed:
As required by the C Standard, HP C supports two new operators that can appear only within macro definitions:
The C Standard also makes specific the sequence in which rescanning and further substitution is to take place, and under what conditions substitution does not take place. The C Standard also specifies under what circumstances a macro may be redefined: only benign redefinition is allowed, permitting a macro to be redefined only if the new definition is token-wise identical to the old definition.
The C Standard specifies that macro substitution can occur on the operands of the #line directive, that the line number operand is restricted to the range 1 to 32,767, and that the file name operand must be treated as any character string literal. VAX C did not support macro substitution on this directive, performed no range checking on the line number, and restricted the length of the character string to 255.
HP C supports macro substitution on the #line directive, diagnoses an out-of-range line number (in strict ANSI C mode only), and allows the file name character string to be as long as the maximum length supported by the compiler for ordinary strings. (Note that the C Standard requires support for a minimum of 509 characters in a string, and that HP C supports strings up to 65,535 characters.)
HP C in both strict ANSI C mode and VAX C mode supports the new #error directive required by the C Standard.
HP C implements #pragma builtins by including the <builtins.h> header file, and is equivalent to #include <builtins.h> on OpenVMS systems.
This header file contains prototype declarations for the built-in functions that allow them to be used properly. By contrast, VAX C implemented this pragma with special-case code within the compiler, which also supported a #pragma nobuiltins preprocessor directive to turn off the special processing. Because declarations cannot be "undeclared," HP C does not support #pragma nobuiltins. Furthermore, the names of all the built-in functions use a naming convention defined by standard C to be in a namespace reserved to the C language implementation.
The #pragma dictionary preprocessor directive replaces the #dictionary directive, but the latter is still supported in VAX C mode for compatibility.
The #pragma dictionary and #dictionary preprocessor directives now allow you to specify whether all string data type variables should be null-terminated.
The #pragma extern_model directive is added to control the compiler's interpretation of objects that have external linkage. This pragma lets you choose the global symbol model to be used for external variables.
The #pragma linkage preprocessor directive allows you to specify special linkage types for function calls.
The #pragma use_linkage directive associates a previously defined special linkage with a function.
The #pragma message directive controls the issuance of individual diagnostic messages or groups of messages. Use of this pragma overrides any command-line options that may affect the issuance of messages.
The #pragma module preprocessor directive replaces the #module directive, but the latter is still supported in VAX C mode for compatibility.
This section describes new features pertaining to the standard header files in the HP C Run-Time Library (RTL).
The wchar_t type is now added to this header file. The declaration of errno is also removed.
Because the C Standard refers to the macros in <ctype.h> as functions, the <ctype.h> header file now includes function prototypes for functions in the HP C RTL that perform the same operations as the macros currently defined in this header file. These functions have been added to the HP C RTL.
The nonstandard toascii macro remains because, according to the C Standard, Section 4.14.2, names beginning with "to" are reserved by the C Standard when <ctype.h> is included.
This header file containing IEEE floating-point class constants has been added to support the new HP C RTL functions fp_class, fp_classf, and fp_classl available on OpenVMS Alpha systems.
The new standard header file <locale.h> is now supported and includes prototypes for the functions setlocale and localeconv, which have been added to the HP C RTL.
The functions cabs and hypot are no longer defined in the <math.h> header file when the compiler is run in strict ANSI C mode.
The SIGABRT signal is implemented and defined in the <signal.h> header file. SIG_ATOMIC_T is now defined as char. In strict ANSI C mode, the following are not declared: ssignal, gsignal, kill, pause, sleep, sigvec, sigblock, sigsetmask, sigstack, and sigpause.
In strict ANSI C mode, the names of the ILL_* and FPE_* macros are changed to begin with "SIG" (for example, SIGILL_RESAD_FAULT, SIGFPE_INTOVF_TRAP, and so on) or be removed.
The BADSIG macro is renamed to SIG_ERR.
The <stdio.h> header file now defines the type size_t and no longer includes <stdarg.h>. The v*printf functions are now prototyped using the type that va_list is defined to be (that is, char *).
In strict ANSI C mode, the following macros are not visible: TRUE, FALSE, SEEK_EOF, OPEN_MAX, L_ctermid, L_cuserid, L_lcltmpnam, L_nettmpnam, and FILE_TYPE. In strict ANSI C mode, the following functions are not visible: fgetname, fdopen, getw, and putw.
The rename function is added.
The fflush function is modified so that a null argument causes it to flush all files.
The printf function is modified to provide the following support:
The scanf function is modified to handle white space as specified by the C Standard. The %p specifier is added. The L flag for long double is added.
The clearerr, feof, and ferror macros are now provided as both macros and functions. By default, they are accessed as macros. To access them as functions, perform an #undef on the macro of the same name. For example:
#undef clearerr |
The <stdlib.h> header file is modified to define size_t and wchar_t directly, rather than including <stddef.h>. The names of the DIV_T and LDIV_T structures now begin with underscores.
The MB_CUR_MAX macro is added.
The multibyte character and string functions mblen, mbtowc, wctomb, mbstowcs and wcstombs are added as specified in Sections 4.10.7 and 4.10.8 of the C Standard.
The abort() function is changed to only raise a SIGABRT signal.
The strcoll and strxfrm functions are added as specified in the C Standard, Sections 4.11.4.3 and 4.11.4.5.
In strict and relaxed modes, the following changes apply to the <time.h> header file:
The mktime and strftime functions are added as specified in the C Standard, Sections 4.12.2.3 and 4.12.3.5, respectively.
HP C for OpenVMS Systems does not support parallel processing on either OpenVMS VAX or OpenVMS Alpha systems and, therefore, does not support the following qualifiers and preprocessor directives:
This appendix contains some of the most common pitfalls you might encounter while using HP C. Symptoms, examples, and solutions are described.
The compiler generates an "Insufficient Virtual Memory" error.
Increase the PAGEFILEQUO process quota and/or the VIRTUALPAGCNT sysgen parameter.
The compiler does not recognize expected routine entry points.
$ type main.c
main()
{
exit(1);
}
$ cc main.c
exit(1);
..^
%CC-I-IMPLICITFUNC, In this statement, the identifier
exit is implicitly declared as a function.
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The compiler generates a %CC-E-NOTCOMPAT error message for seemingly correct code.
$ type main.c
void foo(short a);
void foo(a)
short a;
{}
$ cc main.c
void foo(a)
.....^
%CC-E-NOTCOMPAT, In this declaration, the type of foo is not compatible
with the types of previous declarations of foo.
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This example represents a mixing of new-style function prototypes and old-style function declarations. In the following declaration, the argument a gets widened to int on entry to foo before being converted to type short:
void foo(a) short a; |
Consequently the compiler detects a type mismatch. The example can be generalized to float variables, or any combination of (unsigned) char or short arguments.
void foo();
void foo(a)
short a;
{}
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void foo(short a);
void foo(short a)
{}
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Include-file lookups do not include the anticipated files.
By default, HP C for OpenVMS Systems first searches the directory containing the top-level source file. Consider the following files and the #include statements they contain:
[]main.c
#include "[.sub1]a.h"
[.sub1]a.h
#include "b.h"
[.sub1]b.h
"In [.sub1]"
[.sub2]b.h
"In [.sub2]"
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Compiling with the following command includes the [.sub2]b.h header file:
cc/include=[.sub2]main.c |
Specify /NESTED_INCLUDE_DIRECTORY in order to first search the directory containing the top-level source file (not the directory of the source file containing the #include directive).
VAX C extensions to the language are not accepted by the compiler.
int _align (word) w1; ....^ %CC-W-ALIGNEXT, _align is a language extension. |
Compile using the /STANDARD=VAXC qualifier.
The compiler generates a ADDRCONSTEXT (warning in /STANDARD=RELAXED mode and error in /STANDARD=ANSI mode) for seemingly correct code.
$ type main.c
struct dsc$descriptor_s
{
unsigned short dsc$w_length;
unsigned char dsc$b_dtype;
unsigned char dsc$b_class;
char *dsc$a_pointer;
};
main()
{
char name[5];
struct dsc$descriptor_s name_dsc = {
sizeof(name)-1, 14, 1, name };
}
$ cc main.c
sizeof(name)-1, DSC$K_DTYPE_T, DSC$K_CLASS_S, name };
..............................................^
%CC-W-ADDRCONSTEXT, In the initializer for name_dsc.dsc$a_pointer,
"name" does not have a constant address, but occurs in a context that
requires an address constant. This is an extension of the language.
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Section 3.5.7 of the C Standard restricts allowable automatic aggregate initializion. The HP C compiler does not have this restriction in /STANDARD=VAXC mode. Use any of the following solutions.
static char name[5]; |
#pragma __nostandard
struct dsc$descriptor_s name_dsc = {
sizeof(name)-1, DSC$K_DTYPE_T, DSC$K_CLASS_S, name };
}
#pragma __standard
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