Experimental Physics and
Industrial Control System

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<== Date ==>		<== Thread ==>

Subject:	__STDC_VERSION__ weirdness
From:	Eric Norum <[email protected]>
To:	"EPICS Tech-Talk ([email protected])" <[email protected]>
Date:	Tue, 10 Nov 2015 11:48:33 -0800

I tried to add some code that uses 64 bit integers:

static epicsInt64

scaleCoefficient(double x)

{

    epicsInt64 v;

    int neg = 0;

    if (x < 0) {

        neg = 1;

        x = -x;

}

    if (x > 2) x = 2;

    v = floor(x * (1ULL << 33) + 0.5);

    if (neg) {

        v = -v;

}

    else {

        if (v >= (2ULL << 33)) v = (2ULL << 33) - 1;

}

    return v;

}

To my surprise this failed to compile. The problem is that this test in epicsTypes.h fails:

#if __STDC_VERSION__ >= 199901L

“Hmmmm", I said, “I wonder how that macro expands”...

238> touch a.c

239> gcc -E -dM a.c|grep STDC

#define __STDC_HOSTED__ 1

#define __STDC__ 1

240> 

!!!!!! How can __STDC_VERSION__ be undefined? I thought it was part of the language.

242> type gcc

gcc is hashed (/usr/bin/gcc)

243> gcc --version

gcc (GCC) 4.4.7 20120313 (Red Hat 4.4.7-16)

And indeed, it *is* part of the language — if you explicitly request a more recent standard.

245> gcc -std=c99 -E -dM a.c|grep STDC

#define __STDC_HOSTED__ 1

#define __STDC_VERSION__ 199901L

#define __GNUC_STDC_INLINE__ 1

#define __STDC__ 1

wenorum@xildev4 246> 

My questions, after that long-winded introduction are, “Given that the default gcc options preclude the use of 64 bit values, what -std value should be used? Should the appropriate -std=xxxx be added to CONFIG.gnuCommon?"

--
Eric Norum
[email protected]

Replies:: Re: __STDC_VERSION__ weirdness Andrew Johnson

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ANJ, 16 Dec 2015

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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System