Groups > comp.lang.c > #19847

Re: Generates integer literal of the largest value a variable can hold. Macro takes only variable-name.

From	Ben Pfaff <blp@cs.stanford.edu>
Newsgroups	comp.lang.c
Subject	Re: Generates integer literal of the largest value a variable can hold. Macro takes only variable-name.
Date	2012-04-23 13:36 -0700
Message-ID	<874nsaw5h3.fsf@blp.benpfaff.org> (permalink)
References	<3b194163-c8e2-4250-864a-d3f0a1324677@f5g2000vby.googlegroups.com>

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John Reye <jononanon@googlemail.com> writes:

> Assume you have a variable called
> var
> of unknown type. (Or that the type can be changed).
>
> How can one construct a literal, to be the largest value that this
> variable can hold, without information about the variables type?

The following works for integer types on "ordinary" sytems.

/*
 * Copyright (c) 2008, 2011 Nicira Networks.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at:
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef TYPE_PROPS_H
#define TYPE_PROPS_H 1

#include <limits.h>

#define TYPE_IS_INTEGER(TYPE) ((TYPE) 1.5 == (TYPE) 1)
#define TYPE_IS_SIGNED(TYPE) ((TYPE) 1 > (TYPE) -1)
#define TYPE_VALUE_BITS(TYPE) (sizeof(TYPE) * CHAR_BIT - TYPE_IS_SIGNED(TYPE))
#define TYPE_MINIMUM(TYPE) (TYPE_IS_SIGNED(TYPE) \
                            ? ~(TYPE)0 << TYPE_VALUE_BITS(TYPE) \
                            : 0)
#define TYPE_MAXIMUM(TYPE) (TYPE_IS_SIGNED(TYPE) \
                            ? ~(~(TYPE)0 << TYPE_VALUE_BITS(TYPE)) \
                            : (TYPE)-1)

/* Number of decimal digits required to format an integer of the given TYPE.
 * Includes space for a sign, if TYPE is signed, but not for a null
 * terminator.
 *
 * The value is an overestimate. */
#define INT_STRLEN(TYPE) (TYPE_IS_SIGNED(TYPE) + TYPE_VALUE_BITS(TYPE) / 3 + 1)

#endif /* type-props.h */

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