Q61191: C 6.00 README: Hexadecimal Constants in Strings

Article: Q61191
Product(s): See article
Version(s): 6.00   | 6.00
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | | mspl13_c
Last Modified: 6-NOV-1990

The following information is taken from the C Version 6.00 README.DOC
file.

Hexadecimal Constants in Strings
--------------------------------

Hexadecimal escape sequences in strings now conform to the ANSI
specification by treating every potential hexadecimal digit following
the \x as part of the constant. In C 5.10 and QuickC 2.00, hexadecimal
escape sequences are limited to three characters.

Typically, you will notice this when using hexadecimal escape
sequences for length-preceded strings. Consider the following example:

   char TypeArray[] =
       "\x005float\x006double";

In C 5.10 and QuickC 2.00, TypeArray contains the following bytes:

   <5>float<6>double<0>

In C 6.00, TypeArray has the following bytes:

   _loatmouble<0>

This is because in C 6.00, \x005f and \x006d are legal hexadecimal
sequences that represent the underscore and "m" characters,
respectively.

There are two ways to avoid this problem. The simplest is to use
string concatenation, as follows:

   char TypeArray[] =
       "\x005""float""\x006""double";

According to the ANSI standard, adjacent string literals are
concatenated after escape sequences have been calculated.

A second solution is to use octal, which can never be more than three
digits. The use of octal requires a small calculation and also
requires that you pad out the digits with zeros on the left if
necessary. However, even older, non-ANSI compilers will support this
solution if portability is a concern.

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