HP OpenVMS Systems

The C++ Class Library is a set of headers and other files implementing a collection of basic C++ classes. In the library, these classes are arranged in functionally related groups called packages.

The C++ Class Library makes use of other run-time libraries.

$ set message/nofac/nosev/noid 

1.1 Thread Safe Programming

Developers of multithreaded applications should note the following:

• Internal class library data is thread safe; multiple threads can access the C++ Class Library simultaneously without compromising the integrity of the internal data.
• The predefined stream objects, cerr , cin , clog , and cout are thread safe. However, you need to provide synchronization around sequences of operations on these objects. For more information on synchronizing access to the predefined stream objects, see Chapter 4.
• User-defined objects are not thread safe; users must provide synchronization for such objects if they are shared between threads. For more information on synchronizing access to user-defined objects, see Chapter 6.
• The ios class member function sync_with_stdio() is not thread safe; if your application calls this function, the call must come before any threads use the predefined stream objects: cerr , cin , clog , or cout .
• Generation of error messages within the vector package is not thread safe; the package uses static data members to handle the current error message and there is no synchronization between threads. HP recommends that you define a single Mutex object to synchronize all use of the vector package.
• The task package is not thread safe; only one task can execute at a time.

1.2 Using RMS Attributes with iostreams

The Class Library class fstream constructors amd open() member function do not support different RMS attributes, for example, creating a stream-lf file.

To work around this restriction, use the C library creat() or open() call, which returns a file descriptor, and then use the fstream constructor, which accepts a file descriptor as its argument. For example:

 
 
#include <fstream.hxx> 
 
int main() 
{ 
  int fp; 
 
  // use either creat or open 
  //if ( !(fp= creat("output_file.test", 0, "rfm=stmlf")) ) 
 
  if ( !(fp= open("output_file.test", O_WRONLY | O_CREAT | O_TRUNC , 0, 
"rfm=stmlf")) ) 
    perror("open"); 
 
  ofstream output_file(fp); // use special constructor which takes 
                            // a file descriptor as argument 
  // ... 
} 
 

1.3 Class Library Restrictions

The following are restrictions in the C++ Class Library:

• No Class Library support for 128-bit long doubles
  The Class Library does not include support for 128-bit long doubles.
• Conflict with redefinition of clear()
  If your program includes both <curses.h> and <iostream.hxx> , HP C++ might fail to compile your program because clear() is defined by both header files. In <curses.h> , clear() is defined as a macro whereas in <iostream.hxx> clear() is defined as a member function.
  Workarounds:
  If your program does not use either clear() or uses the <curses.h> clear() , include the <iostream.hxx> header first, followed by <curses.h> .
  If your program uses the ios::clear() function, undefine the clear() macro directly after the #include <curses.h> statement.