What gcc options guarantee more portable C code

[lovecreatesbeauty]

On gcc, which version of C standard has the most compliant: -c89, -ansi
or c99? For more portable C code, which options should be applied to
compilation?

Can the following options guarantee the most portable C code for
different environment?

gcc -ansi -pedantic -Wall test.c
--
lovecreatesbeau ty

[Marc Boyer]

Le 15-06-2006, lovecreatesbeau ty <lo************ ***@gmail.com> a écrit*:

On gcc, which version of C standard has the most compliant: -c89, -ansi
or c99? For more portable C code, which options should be applied to
compilation?

Can the following options guarantee the most portable C code for
different environment?

gcc -ansi -pedantic -Wall test.c

Can't you read the documentation of GCC ?
To compile c89 code, the option is -std=c89.
Support of c99 is not universal today, so, when looking at
'portability', you could restrict yourself to c89.

Other options are there to warn you when you compile some code
that gcc find suspect.

Marc Boyer

[CBFalconer]

lovecreatesbeau ty wrote:

.... snip ... Can the following options guarantee the most portable C code for
different environment?

gcc -ansi -pedantic -Wall test.c

Try "gcc -W -Wall -ansi -pedantic -Wwrite-strings -Wfloat-equal"

--
Chuck F (cb********@yah oo.com) (cb********@mai neline.net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home .att.net> USE maineline address!

[lovecreatesbeauty]

Marc Boyer wrote:

Can't you read the documentation of GCC ?
To compile c89 code, the option is -std=c89.
Support of c99 is not universal today, so, when looking at
'portability', you could restrict yourself to c89.
Other options are there to warn you when you compile some code
that gcc find suspect.

Thank you. But there are total 8933 lines in gcc manual document in
Debian Linux 3.1. Your expertise suggestion can just point out the
right selection from among nearly ten thousand lines of information.

CBFalconer wrote:

Can the following options guarantee the most portable C code for
different environment?
gcc -ansi -pedantic -Wall test.c

Try "gcc -W -Wall -ansi -pedantic -Wwrite-strings -Wfloat-equal"

Thank CBFalconer for the kind help.

lovecreatesbeau ty

[tomstdenis]

CBFalconer wrote:

lovecreatesbeau ty wrote:

... snip ...

Can the following options guarantee the most portable C code for
different environment?

gcc -ansi -pedantic -Wall test.c

Try "gcc -W -Wall -ansi -pedantic -Wwrite-strings -Wfloat-equal"

I dunno if that includes shadows but throw in -Wshadow as well if it
doesn't.

Tom

[lovecreatesbeauty]

to********@gmai l.com wrote:

CBFalconer wrote:

Try "gcc -W -Wall -ansi -pedantic -Wwrite-strings -Wfloat-equal"

I dunno if that includes shadows but throw in -Wshadow as well if it
doesn't.

I check gcc manual again and find that -Wall doesn't cover -Wshadow.
I'm sorry if I misunderstood you.

lovecreatesbeau ty

[tomstdenis]

lovecreatesbeau ty wrote:

to********@gmai l.com wrote:

CBFalconer wrote:

Try "gcc -W -Wall -ansi -pedantic -Wwrite-strings -Wfloat-equal"

I dunno if that includes shadows but throw in -Wshadow as well if it
doesn't.

I check gcc manual again and find that -Wall doesn't cover -Wshadow.
I'm sorry if I misunderstood you.

Then add it. -Wshadow isn't for portability but a lot of beginners
seem to make that mistake, e.g.

int x = 5;
while (somethingelse != 0) {
int x;
for (x = 0; x < 17; x++) { ... }
}
printf("Why is %d==5 it should be 17!!!???\n", x);

Clearly that's a bit contrived but when you use variables like i, j, x,
y, z as loop counters it's trivial to re-use them in nested blocks.

For my code I typically use

-Wall -Wsign-compare -W -Wshadow -Wno-unused-parameter

With at least -O2 or -O3. Turning on optimization is required for
several warnings to fully work.

so if you used

--std=c99 -pedantic -O2 -Wall -Wsign-compare -W -Wshadow
-Wno-unused-parameter

You're likely to catch most common programming mistakes as well as
standards violations. The trick is to not only use these flags but
then ADDRESS the diagnostics raised. Too many people use -Wall then
ignore all the output because "my code is right" syndrome kicks in.

Tom

[Andrew Poelstra]

On 2006-06-15, to********@gmai l.com <to********@gma il.com> wrote:

CBFalconer wrote:

lovecreatesbeau ty wrote:

>

... snip ...

> Can the following options guarantee the most portable C code for
> different environment?
>
> gcc -ansi -pedantic -Wall test.c

Try "gcc -W -Wall -ansi -pedantic -Wwrite-strings -Wfloat-equal"

I dunno if that includes shadows but throw in -Wshadow as well if it
doesn't.

This from Richard Heathfield:
gcc -W -Wall -ansi -pedantic -Wformat-nonliteral -Wcast-align -Wpointer-arith
-Wbad-function-cast -Wmissing-prototypes -Wstrict-prototypes
-Wmissing-declarations -Winline -Wundef -Wnested-externs -Wcast-qual
-Wshadow -Wconversion -Wwrite-strings -Wno-conversion

(You'll have to un-linewrap that a fair bit).

--
Andrew Poelstra < http://www.wpsoftware.net/blog >
To email me, use "apoelstra" at the above address.
I know that area of town like the back of my head.

[John Bode]

lovecreatesbeau ty wrote:

On gcc, which version of C standard has the most compliant: -c89, -ansi
or c99? For more portable C code, which options should be applied to
compilation?

Can the following options guarantee the most portable C code for
different environment?

gcc -ansi -pedantic -Wall test.c

No, because "standard-compliant" does not necessarily imply "portable."
Code that assumes a particular endianness or uses bitfields to model
architecture-specific structures or relies on a platform-specific API
may compile cleanly with the above command, yet still not be portable
(or at least not maximally so).

Don't get me wrong, it's good practice, and it will catch some obvious
errors that may affect portability, but it won't guarantee that the
code is portable.

[CBFalconer]

to********@gmai l.com wrote:

CBFalconer wrote:

lovecreatesbeau ty wrote:

... snip ...

Can the following options guarantee the most portable C code for
different environment?

gcc -ansi -pedantic -Wall test.c

Try "gcc -W -Wall -ansi -pedantic -Wwrite-strings -Wfloat-equal"

I dunno if that includes shadows but throw in -Wshadow as well if
it doesn't.

It doesn't, and adding it is a bad idea. There are times when you
deliberately want to hide an outer scoped identifier, and shadowing
it with a local one is the ideal method.

....
int important; /* critical to the rest of the system */
....
int mybiglongfuncti onNOTusingimpor tant(params) {
....
int local;
int impossible;
...
important = whatever; /* absent minded typo for impossible */
...
}

The above will be perfectly legal coding, but buggy. The bug will
cause total implosion elsewhere. By simply relabelling impossible
as important we prevent such from ever occuring. Shadow good, bug
bad.

--
Chuck F (cb********@yah oo.com) (cb********@mai neline.net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home .att.net> USE maineline address!