Standard Libraries

Compatibility Issues for C++ I/O

This section explains how the SAS/C implementation relates to releases of AT&T C++ and discusses some considerations for developing C++ programs that will adapt easily to the future directions of C++.

AT&T C++ Release 2

The streams library is fully compatible with the AT&T Release 2 streams library. One exception is that member functions that refer to file descriptors and to other aspects of U NIX low-level I/O, such as fd() and attach() , have not been implemented.

AT&T C++ Release 1

The C++ streams library was redefined after the first release, and the Release 2 version is somewhat incompatible with Release 1. (Release 1 is described in Stroustrop's book, The C++ Programming Language, First Edition.) The SAS/C C++ Development System implements the old Release 1 streams library for compatibility with old programs, if you include the old header file stream.h . However, this usage is obsolete and will probably be removed from the library at some point.

stream.h header file

The functions, constants, and types defined in the stream.h header file are provided for compatibility with older versions of some C++ I/O libraries and may not be supported by future versions of the SAS/C C++ I/O library.

All of the functions declared in this header file share an internal static data area and return a pointer to this data area. Each call to any of these functions overwrites this data area.

Here are the contents of the stream.h header file:

char* form(char *format, . . .) ;

provides printf style formatting of character strings. The format string is the same as the format string for the C printf function. (See the description of printf in the SAS/C Library Reference, Volume 1 for more information.) The number and type of the arguments following the format argument are controlled by the format string.

char* oct(long value, int size = 0) ; char* hex(long value, int size = 0) ; char* dec(long value, int size = 0) ; char* chr(long value, int size = 0) ; char* str(char *value, int size = 0) ;

format value into a string and return a pointer to the string.

The following list describes each function in more detail:

oct() formats value as an octal number using the digits 0-7.

hex() formats value as a hexadecimal number using the digits 0-9 and uppercase A-F.

dec() formats value as a decimal number using the digits 0-9.

chr() formats value as a character.

str() formats value as a string.

If size is zero, the returned string is exactly as long as needed to represent the value of 1 . Otherwise, if size is less than the length of the converted value, the converted value is truncated on the right. If size is greater than the length of the converted value, spaces are added to the left of the converted value.

istream& WS(istream& i) ; void eatwhite(istream& i) ;

move the get pointer for i past any white space. If the current character of i is not a white space character, these functions do nothing. A white space character is any character for which the macro isspace returns true. See the SAS/C Library Reference, Volume 1 for a description of isspace .

const int input = ios::in; const int output = ios::out; const int append = ios::app; const int atend = ios::ate; const int _good = ios::goodbit; const int _bad = ios::badbit; const int _fail = ios::failbit; const int _eof = ios::eofbit;

are constants that are passed to or are returned from functions of the I/O library. These names are only provided for compatibility with old programs; the new ios:: style names should be used in new programs. See enum io_state for details on each constant.

typedef ios::io_state state_value;

provides the old name ( state_value ) for what is now defined as ios::io_state . See enum io_state for details on ios::io_state .

Future Directions

ANSI Committee X3J16 is currently working on an official standard for C++, including the streams library. As this work proceeds, it is very likely that there will be additional changes in the specifications of the streams library, some of which may cause existing programs to fail. It is therefore recommended that C++ streams applications should be kept relatively simple, to lessen the chances of disturbance by redefinition of some of the more obscure parts of the library. Especially, we recommend that you avoid deriving from the streambuf classes, as this interface is infrequently used and is expected to be volatile.

Note: There is not yet an ANSI Standard for C++, but when one is developed, the SAS/C C++ Development System will comply with this Standard. At such time, ANSI compatibility will take precedence over compatibility with the C++ language described in The C++ Programming Language. [cautionend]

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`oct()`	formats `value` as an octal number using the digits 0-7.
`hex()`	formats `value` as a hexadecimal number using the digits 0-9 and uppercase A-F.
`dec()`	formats `value` as a decimal number using the digits 0-9.
`chr()`	formats `value` as a character.
`str()`	formats `value` as a string.