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HP C++
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HP C++ implements the International C++ Standard, with some differences, as described in the HP C++ Release Notes for Tru64 UNIX .
This language differs significantly from The Annotated C++ Reference Manual, implemented by the Version 5.n compilers. When switching from a Version 5.n compiler, you might need to modify your source files, especially if you use the default language mode. In addition, language changes can affect the run-time behavior of your programs. If you want to compile existing source code with minimal source changes, compile using the -std arm option. See The C++ Standard Library for information on and changes to the Standard Library.
This chapter describes ways to avoid having the compiler reject program code that previously worked with other C++ implementations that adhere less strictly to the C++ language definition. References to applicable portions of The C++ Programming Language, 3rd Edition indicate where you can find additional help.
In default mode ( -std ansi ), the compiler implements most features of the International C++ Standard including:
For compatibility with previous versions, the compiler provides the following language mode options:
-std ansi
Specify this option if you want an ANSI C++ compiler that supports some commonly used extensions and is somewhat less strict than the standard. This is the default compiler mode.If you want to use ANSI mode but find that the compiler generates too many diagnostics in that mode, you can use the -msg_quiet option with the -std ansi option. The -msg_quiet option relaxes error checking and suppresses or reduces the severity of many diagnostics. It also suppresses many warnings that are generated in ANSI mode but were not issued by Version 5.6. For information on message control options, see Message Control Options in Chapter 2 .
-std arm
Specify this option if you want to compile programs developed using Version 5.n and want to minimize source changes.If you usually want your compilations done in this mode and don't want to specify -std arm on each cxx command, define environment variable DEC_CXX as follows:
setenv DEC_CXX "-std arm"You can place a single vertical bar ("|") within the variable. All arguments preceding the bar are evaluated before any explicit command-line arguments; all arguments following the bar are evaluated afterwards. In the absence of a vertical bar, all arguments are evaluated before the explicit command-line arguments.
Specify -v to obtain the definition of DEC_CXX For example, assuming the definition of DEC_CXX above, the cxx -v command results in the following:
% cxx -v $DEC_CXX contains: -std armTo enhance compatibility with other C++ compilers, HP C++ supports options that direct the compiler to interpret the source program according to certain rules followed by other implementations:
-std cfront
As of C++ Version 7.1, this option is no longer supported.-std gnu
Use this option if you want to compile programs developed using the GNU compiler. This option also defines the __STD_GNU macro. The following changes in behavior are provided for compatibility with the GNU C++ compiler:
- These options are enabled by default:
-alternative_tokens, -tlocal, and -no_implicit_include- Access control is not enforced for types defined inside a class.
- Unrecognized character escape sequences in string literals produce an informational instead of a warning message.
- The __inline keyword is enabled and is equivalent to inline .
- When overloading, enum types are treated as integral types.
The following known incompatibilities are not addressed in the -std gnu mode:
- The compiler strictly enforces the requirement to define functions before they are used. This requirement also applies to built-in functions such as strlen .
-std ms
Specify this option if you want the compiler to accept additional Microsoft Visual C++ extensions.-std strict_ansi
Specify this option if you want the compiler to enforce the ANSI C++ standard strictly but permit some ANSI violations that should be errors to be warnings.-std strict_ansi_errors
Specify this option if you want strict_ansi and also want errors to be issued for all ANSI violations.
With -std ms you might also want to specify -msg_quiet to reduce the number of diagnostic messages generated. For details, see Message Control Options in Chapter 2 .
This section provides information about differences between the current compiler and Version 5.n compilers.
This release provides the following compiler version options:
-newcxx
Invokes the Version 6.3 compiler. This is the default.-oldcxx
Invokes a bug fix update to the Version 5.7 compiler.The -oldcxx option is provided for cases where the Version 6.n compiler requires excessive source changes or for problems in using that compiler. If extensive source changes are required to correct errors, try using the -std arm option. For excessive warnings, try the -msg_quiet option.
If you want -oldcxx to be the default, define the DEC_CXX environment variable as follows:
setenv DEC_CXX "-oldcxx"
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Before you can use the -oldcxx option, the optional -oldcxx subset must be installed. See the HP C++ Installation Guide for Tru64 UNIX .
Be aware of the following language differences between the current compiler and Version 5.n compilers:
bool, const_cast, explicit, export, false, mutable, dynamic_cast, reinterpret_cast, static_cast, truce, typeid, typename, wchar_t |
and, and_eq, bitand, bitor, compl, not, not_eq, or, or_eq, xor, xor_eq |
typedef void (*PF)(); // Pointer to an extern "C++" function extern "C" typedef void (*PCF)(); // Pointer to an extern "C" function void f(PF); void f(PCF); |
#include <iostream.h>
struct A {
int a;
};
struct D : public virtual A
{
A* toA(){ return (A*) this; }
};
main ()
{
D* d = NULL;
A* ad = d->toA(); // will seg fault
if (ad==NULL) cout << "ok";
}
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volatile int *vptr; int *ptr=vptr;
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typedef void Z::* any_ptom; |
Users should be aware of the following implementation differences between the current and previous versions of the compiler:
f(const int p1);
f(int p1);
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f(i++, i++);
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Aspects of memory allocation and deallocation have changed. For detailed information, see The C++ Standard Library .
This section discusses porting issues pertaining to C++ classes.
When making friend declarations, use the elaborated form of type specifier. The following code fragment implements the legal and comments out the illegal friend declaration:
class Y; class Z; class X; //friend Y; ** not legal friend class Z; // legal }; |
Unlike some older C++ implementations, HP C++ strictly enforces accessibility rules for public , protected , and private members of a base class. For more information, see The C++ Programming Language, 3rd Edition.
Unlike some older C++ implementations, HP C++ requires you to use the base class name in the initializer for a derived class. The following code fragment implements a legal initializer and comments out an illegal initializer:
class Base {
// ...
public:
Base (int);
};
class Derived : public Base {
// ...
public:
// Derived(int i) : (i) {/* ...*/} ** not legal
Derived(int i) : Base(i) {/* ...*/} // ** legal, supplies class name
};
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For more information, see The C++ Programming Language, 3rd Edition.
When a static data member is declared, the compiler issues a reference to the external identifier in the object code, which must be resolved by a definition. On HP Tru64 UNIX and Linux Alpha systems, the compiler does not support the declaration anachronism shown in The C++ Programming Language, 3rd Edition.
For example, consider the following code fragment:
#include <stdio.h>
class C {
public:
static int i;
};
//missing definition
//int C::i = 5;
int main ()
{
int x;
x=C::i;
printf("x %d\n",x);
return 0;
}
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The compiler does not issue any messages during compilation; however, when you attempt to link a program containing this code, the linker issues a message similar to the following:
ld: Error: Undefined: i__1C |
HP C++ requires the use of function definitions as described in The C++ Programming Language, 3rd Edition. For examples of outdated syntax not allowed in HP C++, see The C++ Programming Language, 3rd Edition.
Because all linkage specifications for a name must agree, function prototypes are not permitted if the function is later declared as an inline function. The following code is an example of such a conflicting function declaration:
int f();
inline int f() { return l; }
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In this example, f is declared with both internal and external linkage, which causes a compiler error.
Similarly, the declaration int f(i,j) causes an error even when the declaration is defined with the "C" linkage specification, because the linkage specification has no effect on the semantics of the declaration.
This section explains how to use pointers effectively in HP C++.
In HP C++, you cannot implicitly convert a const pointer to a nonconstant pointer. For example, char * and const char * are not equivalent; explicitly performing such a cast can lead to unexpected results.
For more information, see The C++ Programming Language, 3rd Edition.
Binding a pointer to a member function with a particular object as an argument to the function is not allowed in HP C++. For more information on the illegality of casting bound pointers, see The C++ Programming Language, 3rd Edition.
Because the return value cannot be an lvalue, a constant in a function return has no effect on the semantics of the return. However, using a constant in a function return does affect the type signature. For example:
static int f1( int a, int b) {;}
const int (* const (f2[])) (int a, int b) = {f1};
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In this example, the referenced type of the pointer value f1 in the initializer for f2[] is function (signed int, signed int) , which returns signed int . This is incompatible with function (signed int, signed int) , which returns const signed int .
You can omit the const of int because it affects only the constant return signature.
The following example shows a type mismatch between a pointer to a char and a pointer to a const char :
void foo (const char* argv[]) {}
int main()
{
static char* args[2] = {"foo","bar"};
/* 'In this statement, the referenced type of the pointer value
"args" is "pointer to char"' which is not compatible with
"pointer to const char"'*/
foo (args);
return 0;
}
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You can correct this example by changing static char to static const char . Use an explicit type cast to get an argument match only if no other option is available; such a cast may break on some C++ implementations.
Using a synonym after a class , struct , or union prefix is illegal. Using a synonym in the names for constructors and destructors within the class declaration itself is also illegal.
In the following example, the illegal typedef specifier is commented out:
typedef struct { /* ...*/ } foo;
// typedef struct foo foobar; ** not legal
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For more information, see The C++ Programming Language, 3rd Edition.
HP C++ warns against initializing nonconstant references to refer to temporary objects. The following example demonstrates the problems that can result:
static void f()
{
int i = 5;
i++; // OK
int &ri = 23;
ri++; // In the initializer for ri, the initialization of a
// non-const reference requires a temporary for "23".
}
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The issue of reference initialization arises most often in assignment operators and in copy constructors. Wherever possible, declare all reference arguments as const .
For more information, see The C++ Programming Language, 3rd Edition.
Branching around a declaration with an explicit or implicit initializer is not legal, unless the declaration is in an inner block that is completely bypassed. To satisfy this constraint, enclose the declaration in a block. For example:
int i;
switch (i) {
case 1:
int l = 0; //not initialized at this case label
myint m = 0; //not initialized at this case label
{
int j = 0; // legal within the braces
myint m = 0; // legal within the braces
}
case 2:
break;
// ...
}
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For more information on using the switch statement, see of The C++ Programming Language, 3rd Edition.
You must supply the meaning of copy constructing and assigning from volatile objects, because the compiler generates no copy constructors or assignment operators that copy or assign from volatile objects. The following example contains examples of such errors, as noted in the comments:
class A {
public:
A() { }
// A(volatile A&) { }
// operator=(volatile A&) { return 0; }
};
void foo()
{
volatile A va;
A a;
A cca(va); // error - cannot copy construct from volatile object
a = va; // error - cannot assign from volatile object
return;
}
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For more information, see The C++ Programming Language, 3rd Edition.
HP C++ allows identifiers, but not expressions, on the #ifdef preprocessor directive. For example:
// this is not legal // #ifdef KERNEL && !defined(__POSIX_SOURCE) |
The following is the legal alternative:
// use this instead #if defined(KERNEL) && !defined(__POSIX_SOURCE) |
For more information, see The C++ Programming Language, 3rd Edition.
The proper way to manage memory for a class is to overload the new and delete operators. This is in contrast to some older C++ implementations, which let you manage memory through assignment to the this pointer.
For more information, see The C++ Programming Language, 3rd Edition.
Program developers must take care that any user-defined new operators always return pointers to quadword aligned memory.
If a size-of-array argument accompanies a delete operator, the compiler ignores the argument and issues a warning. The following example includes an anachronistic use of the delete operator:
int main()
{
int *a = new int [20];
int *b = new int [20];
delete[20] a; //old-style; argument ignored, warning issued
delete[] b;
return 0;
}
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Do not depend on the newline character (\ n ) to flush your terminal output buffer. A previous stream implementation might have done so, but this behavior is not in conformance with Version 2.0 of the AT&T iostream library. If you want to flush the output buffer, use the endl manipulator or the flush member function.
Situations occur in which a simple typographical error generates a missing parenthesis error message. In the following example, the class name CaseSensitive is incorrectly specified as Casesensitive in the constructor declaration:
class CaseSensitive {
void Test( const Casesensitive &foo );
};
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As the compiler parses the argument declaration list:
Among the next legal tokens are the equal sign, comma, and closing parenthesis. Upon finding an ampersand, the compiler expects a closing parenthesis. With all other possibilities exhausted, the compiler has what appears to be a legal argument declaration list, after which the closing parenthesis is the only allowable token. The compiler expected one thing but encountered something else. Often, inserting newline characters can isolate the offending token.
Use the cxx command, not the ld command, to build a binary; otherwise, the run-time startup and other crucial code will not build properly. Some symptoms of linking incorrectly are
HP C++ automatically treats files with a .c extension as C language source files and passes the files to the cc command. For HP C++ to compile them, your files must have one of the following extensions:
.cxx .CXX .cpp .CPP .cc .CC .C .C++ |
You also can use the -x option to direct the compiler to ignore file-name extensions and treat all named files, other than those with an .a or .o extension, as C++ source files.
Some other C++ implementations let you perform integer arithmetic, including ++, on enumerated types; HP C++ does not allow this.
If the for-init-statement is a declaration, the scope of the name(s) declared extends to the end of the for-statement, as shown in the following example:
int i=5;
void f()
{
for (int i=0;i<10;i++);
printf("%d\n",i);
}
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When compiled -std ansi , strict_ansi , or strict_ansi_errors , the compiler produces the results expected by the International C++ Standard. In all other modes, the compiler produces the results expected by The Annotated C++ Reference Manual; that is, the scope of the names declared extends to the end of the enclosing scope.
Paying careful attention to data types can ensure that your code works on both 32-bit and 64-bit systems. Use the following guidelines to write clean 64-bit code:
long foo, bar; foo = 1L << bar; |
For more information, see the ULTRIX to HP Tru64 UNIX Migration Guide.
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