questions about constants

[Martin Johansen]

Hello

I was not able to find answers to there Qs on google or in the FAQ, so
here goes

Q1:
I refer to the question 2.10 in the FAQ
the following code compiled with gcc
(struct {int a; char* b; int c;}){1, "1", 'A'}.c
but is it valid ansi c?

Q2:
Are these equivalent?
(long)1 contra 1L

Q3:
I know of the following "constant classifiers" i.e. 1L
l and L, f and F, u and U
but are there more?

Thank you!

[Kevin Bracey]

In message <nT******************@news4.e.nsc.no>
Martin Johansen <mf**@online.no> wrote:

Hello

I was not able to find answers to there Qs on google or in the FAQ, so
here goes

Q1:
I refer to the question 2.10 in the FAQ
the following code compiled with gcc
(struct {int a; char* b; int c;}){1, "1", 'A'}.c
but is it valid ansi c?
It's valid in ISO C99, but not earlier versions.
Q2:
Are these equivalent?
(long)1 contra 1L
Yes, for that specific example, barring syntax quirks (eg "sizeof (long)1"
will be parsed differently from "sizeof 1L").

This might not be:

(long)1000000000000 vs 1000000000000L

because the suffix only specifies a minimum size, and it will grow to
long long if necessary. The first form would truncate it back down to long,
even if it didn't fit.
Q3:
I know of the following "constant classifiers" i.e. 1L
l and L, f and F, u and U
but are there more?

C99 has "ll" or "LL" for long long.

--
Kevin Bracey, Principal Software Engineer
Tematic Ltd Tel: [phone]
182-190 Newmarket Road Fax: [phone]
Cambridge, CB5 8HE, United Kingdom WWW: http://www.tematic.com/

[Martin Dickopp]

Martin Johansen <mf**@online.no> writes:

Q1:
I refer to the question 2.10 in the FAQ
the following code compiled with gcc
(struct {int a; char* b; int c;}){1, "1", 'A'}.c
but is it valid ansi c?
This is called a compound literal; it is valid according to the current
ISO C standard (C99). Note, however, that most compilers do not yet
implement C99, but C89, the previous C standard. (GCC implements C99
only partially.)
Q2:
Are these equivalent?
(long)1 contra 1L
Yes.
Q3:
I know of the following "constant classifiers" i.e. 1L
l and L, f and F, u and U
but are there more?

For integers, there are the suffixes L (long), U (unsigned), and UL
(unsigned long), and in C99 LL (long long) and ULL (unsigned long long).
For floating-point numbers, there are F (float) and L (long double). All
suffixes can be spelled in uppercase or lowercase letters.

Martin
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