Raeburn@ATHENA.MIT.EDU (Ken Raeburn) (01/05/90)
(version 1.36.1, vax)
Source file:
extern "C" {
extern void foo (struct frob *);
};
struct frob {
int a, b;
};
Results:
% g++ -O -v -g -c bar.c
gcc version 1.36.1 (based on GCC 1.36)
/mit/gnu/vaxlib/gcc-cpp -+ -v -undef -D__GNUC__ -D__GNUG__ -D__cplusplus -Dvax -Dunix -D__vax__ -D__unix__ -D__OPTIMIZE__ bar.c /usr/tmp/cc005284.cpp
GNU CPP version 1.36
/mit/gnu/vaxlib/gcc-cc1plus /usr/tmp/cc005284.cpp -fcombine-regs -fstrength-reduce -quiet -dumpbase bar.c -g -O -version -o /usr/tmp/cc005284.s
GNU C++ version 1.36.1 (based on GCC 1.36) (vax) compiled by GNU C version 1.36.
default target switches:
bar.c:7: Segmentation violation
g++: Program cc1plus got fatal signal 11.
-- Kenpcg@aber-cs.UUCP (Piercarlo Grandi) (01/07/90)
In article <9001051018.AA05287@multics.MIT.EDU> Raeburn@ATHENA.MIT.EDU (Ken Raeburn) writes: (version 1.36.1, vax) Source file: extern "C" { extern void foo (struct frob *); }; struct frob { int a, b; }; and it chokes.... Too bad :->. In any case, you *should not* put a semicolon at the end of an extern "C" block. This is also the likely reason of the core dump, because using 'struct some *' before having seen 'struct some { ....' is legal and without problem in both C and C++, or else mutually "recursive" data structures would not be possible. -- Piercarlo "Peter" Grandi | ARPA: pcg%cs.aber.ac.uk@nsfnet-relay.ac.uk Dept of CS, UCW Aberystwyth | UUCP: ...!mcvax!ukc!aber-cs!pcg Penglais, Aberystwyth SY23 3BZ, UK | INET: pcg@cs.aber.ac.uk
T.Day@ucl-cs.UUCP (01/09/90)
From: Tim Day <T.Day@uk.ac.ucl.cs> Piercarlo "Peter" Grandi writes: > using 'struct some *' before having seen 'struct some {...' > is legal and without problem in both C and C++ Not quite. You have to say struct frob; before you can use pointers or references to frob. Inserting this line at the start of your example code causes it compile OK (on a Sun3). The core dump instead of error message is still a bug though. +-----------------------------------------------------------------------------+ Tim Day | Meet every second in life as challenge; Department of Photogrammetry | Respond fully to whatever happens UCL, Gower St., London WC1E 6BT | without anxiety, or complaint, or clinging +-----------------------------------------------------------------------------+
pcg@aber-cs.UUCP (Piercarlo Grandi) (01/12/90)
In article <494@ucl-cs.UUCP> T.Day@ucl-cs.UUCP writes: From: Tim Day <T.Day@uk.ac.ucl.cs> Piercarlo "Peter" Grandi writes: > using 'struct some *' before having seen 'struct some {...' > is legal and without problem in both C and C++ Not quite. You have to say struct frob; before you can use pointers or references to frob. Not really, neither in C nor in C++. Try compiling: struct a {struct b *b;} a; struct b {struct a *a;} b; It shall work, both in C and C++. There has never been a requirement that the name of a struct be known before its use, if its use is to declare a pointer to the struct. The compiler need not bother; anything that comes after 'struct' must be a struct name, and a pointer has always the same size. You are confusing this point with the the fact that in C++, saying 'struct a;', which in it as well as in C++ is an empty declaration, and no special construct all, also has the effect of typedef'ing 'a' as 'struct a'. The compiler needs to know that a name is a typedef, otherwise parsing declarations cannot be done. In this, the C++ practice of saying 'class c;' is NOT a forward declaration; it i just the old harmless practice of having empty declarations, coupled with the new side effect of having an implicit typedef. Saying beforehand 'class c;' in C++ is not needed if you write 'class c *m;' instead of 'c *m;'. The effect is the same if you just say 'typedef class a ;'. With the following preprocessor macro you get the same effect in C: #define mode(FLAVOR,NAME) \ typedef FLAVOR NAME NAME; FLAVOR NAME Note that the typedef appears *before* the struct definition, if any; if you follow this with a ';' the struct definition becomes a harmless empty delcaration. You can use this in C as mode(struct,complex) { float re,im; }; complex a,b,c; or mode(struct,clutch); mode(struct,car) { ...; clutch *theClutch; ... }; just like in C++, if you have got fed up with using leading 'struct', 'union', 'enum' (enums are special though in C)... -- Piercarlo "Peter" Grandi | ARPA: pcg%cs.aber.ac.uk@nsfnet-relay.ac.uk Dept of CS, UCW Aberystwyth | UUCP: ...!mcvax!ukc!aber-cs!pcg Penglais, Aberystwyth SY23 3BZ, UK | INET: pcg@cs.aber.ac.uk