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Commit 498ec23d by Steven Bosscher Committed by Steven Bosscher
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README.Portability: Remove K+R section. 

2003-12-10  Steven Bosscher  <stevenb@suse.de>

	* README.Portability: Remove K+R section.

	* gengtype-lex.l: Teach about "void**" pointers and
	"void*" function types.

From-SVN: r74501
parent ed1fe829
Showing with 14 additions and 211 deletions
gcc/ChangeLog
2003-12-10 Steven Bosscher <stevenb@suse.de>
* README.Portability: Remove K+R section.
* gengtype-lex.l: Teach about "void**" pointers and
"void*" function types.
2003-12-10 Eric Botcazou <ebotcazou@libertysurf.fr>
PR target/13354
......
gcc/README.Portability
......@@ -14,18 +14,15 @@ I'm going to start from a base of the ISO C89 standard, since that is
probably what most people code to naturally. Obviously using
constructs introduced after that is not a good idea.
The first section of this file deals strictly with portability issues,
the second with common coding pitfalls, and the third with obsolete
K+R portability issues.
For the complete coding style conventions used in GCC, please read
http://gcc.gnu.org/codingconventions.html
Portability Issues
==================
String literals
---------------
Some SGI compilers choke on the parentheses in:-
Irix6 "cc -n32" and OSF4 "cc" have problems with constant string
initializers with parens around it, e.g.
const char string[] = ("A string");
......@@ -176,7 +173,7 @@ WITH UMLAUT.
Other common pitfalls
---------------------
o Expecting 'plain' char to be either sign or unsigned extending
o Expecting 'plain' char to be either sign or unsigned extending.
o Shifting an item by a negative amount or by greater than or equal to
the number of bits in a type (expecting shifts by 32 to be sensible
......@@ -198,204 +195,3 @@ o Passing incorrect types to fprintf and friends.
o Adding a function declaration for a module declared in another file to
a .c file instead of to a .h file.
K+R Portability Issues
======================
Unary +
-------
K+R C compilers and preprocessors have no notion of unary '+'. Thus
the following code snippet contained 2 portability problems.
int x = +2; /* int x = 2; */
#if +1 /* #if 1 */
#endif
Pointers to void
----------------
K+R C compilers did not have a void pointer, and used char * as the
pointer to anything. The macro PTR is defined as either void * or
char * depending on whether you have a standards compliant compiler or
a K+R one. Thus
free ((void *) h->value.expansion);
should have been written
free ((PTR) h->value.expansion);
Further, an initial investigation indicates that pointers to functions
returning void were okay. Thus the example given by "Calling
functions through pointers to functions" below appeared not to cause a
problem.
String literals
---------------
K+R C did not allow concatenation of string literals like
"This is a " "single string literal".
signed keyword
--------------
The signed keyword did not exist in K+R compilers; it was introduced
in ISO C89, so you could not use it. In both K+R and standard C,
unqualified char and bitfields may be signed or unsigned. There is no
way to portably declare signed chars or signed bitfields.
All other arithmetic types are signed unless you use the 'unsigned'
qualifier. For instance, it was safe to write
short paramc;
instead of
signed short paramc;
If you have an algorithm that depends on signed char or signed
bitfields, you had to find another way to write it before it could be
integrated into GCC.
Function prototypes
-------------------
You need to provide a function prototype for every function before you
use it, and functions had to be defined K+R style. The function
prototype should have used the PARAMS macro, which takes a single
argument. Therefore the parameter list had to be enclosed in
parentheses. For example,
int myfunc PARAMS ((double, int *));
int
myfunc (var1, var2)
double var1;
int *var2;
{
...
}
This implies that if the function takes no arguments, it had to be
declared and defined as follows:
int myfunc PARAMS ((void));
int
myfunc ()
{
...
}
You also had to use PARAMS when referring to function protypes in
other circumstances, for example see "Calling functions through
pointers to functions" below.
Variable-argument functions are best described by example:-
void cpp_ice PARAMS ((cpp_reader *, const char *msgid, ...));
void
cpp_ice VPARAMS ((cpp_reader *pfile, const char *msgid, ...))
{
VA_OPEN (ap, msgid);
VA_FIXEDARG (ap, cpp_reader *, pfile);
VA_FIXEDARG (ap, const char *, msgid);
...
VA_CLOSE (ap);
}
See ansidecl.h for the definitions of the above macros and more.
One aspect of using K+R style function declarations, is you could not
have arguments whose types are char, short, or float, since without
prototypes (ie, K+R rules), these types are promoted to int, int, and
double respectively.
Calling functions through pointers to functions
-----------------------------------------------
K+R C compilers require parentheses around the dereferenced function
pointer expression in the call, whereas ISO C relaxes the syntax. For
example
typedef void (* cl_directive_handler) PARAMS ((cpp_reader *, const char *));
*p->handler (pfile, p->arg);
had to become
(*p->handler) (pfile, p->arg);
Macros
------
The rules under K+R C and ISO C for achieving stringification and
token pasting are quite different. Therefore some macros have been
defined which will get it right depending upon the compiler.
CONCAT2(a,b) CONCAT3(a,b,c) and CONCAT4(a,b,c,d)
will paste the tokens passed as arguments. You must not leave any
space around the commas. Also,
STRINGX(x)
will stringify an argument; to get the same result on K+R and ISO
compilers x should not have spaces around it.
Passing structures by value
---------------------------
You had to avoid passing structures by value, either to or from
functions. It seems some K+R compilers handle this differently or not
at all.
Enums
-----
In K+R C, you had to cast enum types to use them as integers, and some
compilers in particular give lots of warnings for using an enum as an
array index.
Bitfields
---------
See also "signed keyword" above. In K+R C only unsigned int bitfields
were defined (i.e. unsigned char, unsigned short, unsigned long.
Using plain int/short/long was not allowed).
Reserved Keywords
-----------------
K+R C has "entry" as a reserved keyword, so you had to not use it for
your variable names.
Type promotions
---------------
K+R used unsigned-preserving rules for arithmetic expresssions, while
ISO uses value-preserving. This means an unsigned char compared to an
int is done as an unsigned comparison in K+R (since unsigned char
promotes to unsigned) while it is signed in ISO (since all of the
values in unsigned char fit in an int, it promotes to int).
Suffixes on Integer Constants
-----------------------------
K+R C did not accept a 'u' suffix on integer constants. If you wanted
to declare a constant to be be unsigned, you had to use an explicit
cast.
gcc/gengtype-lex.l
......@@ -146,7 +146,7 @@ ITYPE {IWORD}({WS}{IWORD})*
update_lineno (yytext, yyleng);
}
[^[:alnum:]_]typedef{WS}{ID}{WS}?"("{WS}?"*"{WS}?{ID}{WS}?")"{WS}?PARAMS {
[^[:alnum:]_]typedef{WS}{ID}{WS}?"*"?{WS}?"("{WS}?"*"{WS}?{ID}{WS}?")"{WS}?PARAMS {
char *namestart;
size_t namelen;
struct type *t;
......@@ -162,7 +162,7 @@ ITYPE {IWORD}({WS}{IWORD})*
update_lineno (yytext, yyleng);
}
[^[:alnum:]_]typedef{WS}{ID}{WS}?"("{WS}?"*"{WS}?{ID}{WS}?")"{WS}?"(" {
[^[:alnum:]_]typedef{WS}{ID}{WS}?"*"?{WS}?"("{WS}?"*"{WS}?{ID}{WS}?")"{WS}?"(" {
char *namestart;
size_t namelen;
struct type *t;
......
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