JTC1/SC22/WG14 N609

                     Document Number:  WG14 N609/X3J11 96-073


                         C9X Revision Proposal
                         =====================

 Title: Boolean as a new type
 Author: Frank Farance
 Author Affiliation: Farance Inc.
 Postal Address: 555 Main Street, New York, NY, 10044-0150, USA
 E-mail Address: [email protected]
 Telephone Number: +1 212 486 4700
 Fax Number: +1 212 759 1605
 Sponsor: X3J11
 Date: 1996-09-13
 Proposal Category:
    __ Editorial change/non-normative contribution
    __ Correction
    X_ New feature
    __ Addition to obsolescent feature list
    __ Addition to Future Directions
    __ Other (please specify)  ______________________________
 Area of Standard Affected:
    __ Environment
    X_ Language
    __ Preprocessor
    __ Library
       __ Macro/typedef/tag name
       __ Function
       __ Header
 Prior Art: C++
 Target Audience: C programmers
 Related Documents (if any):
 Proposal Attached: X_ Yes __ No, but what's your interest?

 This proposal is for adding boolean as a new type, not just
 a macro for an existing integer type.  The following
 problems need to be resolved with a boolean type:

         1.  It is a keyword, or hidden magic turned on by
         including a header?

         2.  What is its type?  A new C type or an existing
         one?

         3.  What are the promotion rules?

         4.  What about use of "false" and "true" in the
         preprocessor?

         5.  What is the migration strategy?

 Answer #1: For compatibility reasons, we need to have a
 header that turns on this feature: "#include <bool.h>".  The
 type is "bool" with values "false" and "true".

 Answer #2: In previous proposals, the type "bool" was a
 macro (or typedef) for an existing C integral type.  This
 has raised some issues with respect to promotion rules for
 certain scenarios.  I propose that we make "bool" a real,
 separate C type.

 Answer #3: Promotion from "bool" to other types produces the
 values 0 or 1.  Demotion from other types to bool follows
 the rules: equal to 0 ==> false, not equal to 0 ==> true.

 Answer #4: The macros "false" and "true" will equate to 0
 and 1 respectively.

 Answer #5: The header "<bool.h>" will be used to avoid
 breaking existing programs.  The macro

         __bool_true_false_are_defined

 will be defined when the implementation defines (as macros
 or keywords) the boolean type via the "#include <bool.h>"
 header.  We should indicate that it is our intent to make
 "bool" a keyword in the next revision of the Standard.
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()0(ISO/JTC1/SC22/WG14/N604    Page 1)8 L
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()0(Document Number:  WG14 N604/X3J11 96-068)28 L
()l
()l
()0(C9X Revision Proposal)32 L
()0(=====================)32 L
()l
()0(Title: Proposal to fix "ungetc" for beginning of file.)8 L
()0(Author: Frank Farance)8 L
()0(Author Affiliation: Farance Inc.)8 L
()0(Postal Address: 555 Main Street, New York, NY, 10044-0150, USA)8 L
()0(E-mail Address: [email protected])8 L
()0(Telephone Number: +1 212 486 4700)8 L
()0(Fax Number: +1 212 759 1605)8 L
()0(Sponsor: X3J11)8 L
()0(Date: 1996-09-13)8 L
()0(Proposal Category:)8 L
()0(__ Editorial change/non-normative contribution)11 L
()0(X_ Correction)11 L
()0(__ New feature)11 L
()0(X_ Addition to obsolescent feature list)11 L
()0(__ Addition to Future Directions)11 L
()0(__ Other \(please specify\)  ______________________________)11 L
()0(Area of Standard Affected:)8 L
()0(__ Environment)11 L
()0(__ Language)11 L
()0(__ Preprocessor)11 L
()0(X_ Library)11 L
()0(__ Macro/typedef/tag name)14 L
()0(X_ Function)14 L
()0(__ Header)14 L
()0(Prior Art:)8 L
()0(Target Audience: C programmers)8 L
()0(Related Documents \(if any\):)8 L
()0(Proposal Attached: X_ Yes __ No, but what's your interest?)8 L
()l
()0(This proposal is for making "ungetc\(\)" undefined at the)8 L
()0(beginning of a file.  Currently, the Standard allows the)8 L
()0(programmer to push back a character at the beginning of a)8 L
()0(file.  While this ``feature'' \(a relic from certain I/O)8 L
()0(library implementations\) is allowed, there is no practical)8 L
()0(value for pushing back a character prior to reading the)8 L
()0(first character in a file.  The direct consequence of this)8 L
()0(is that properly coding a ``mark and return'' feature with)8 L
()0("ftell\(\)" and "fseek\(\)" becomes overly complex and error-)8 L
()0(prone because \(1\) "ftell\(\)" can return -1 as a *valid* file)8 L
()0(position, \(2\) the programmer must provide he/her own)8 L
()0(mechanism for saving the character when performing a ``mark)8 L
()0(and return'' in this special case, \(3\) this special case)8 L
()0(causes much non-localized behavior, e.g., the)8 L
()0(reading/parsing, the marking of position, and the returning)8 L
()0(to position functions all have interrelated design, code,)8 L
()0(and state \(!\) flags rather than being independent features.)8 L
()0(Changing this behavior would reduce the complexity of)8 L
()0(writing applications and libraries that comply with the)8 L
()0(Standard.)8 L
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()0(ISO/JTC1/SC22/WG14/N604    Page 2)8 L
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()0(Current wording in "ungetc", 7.9.6.11:)8 L
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()0(^^^^^)63 L
()0(indeterminate after the call.)16 L
()0(^^^^^^^^^^^^^^^^^^^^^^^^^^^^)16 L
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()0(behavior is undefined.)16 L
()0(^^^^^^^^^^^^^^^^^^^^^)16 L
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()0(ISO/JTC1/SC22/WG14/N606    Page 1)8 L
()l
()l
()0(Document Number:  WG14 N606/X3J11 96-070)28 L
()l
()l
()0(C9X Revision Proposal)32 L
()0(=====================)32 L
()l
()0(Title: Extended integers promotion rules)8 L
()0(Author: Frank Farance)8 L
()0(Author Affiliation: Farance Inc.)8 L
()0(Postal Address: 555 Main Street, New York, NY, 10044-0150, USA)8 L
()0(E-mail Address: [email protected])8 L
()0(Telephone Number: +1 212 486 4700)8 L
()0(Fax Number: +1 212 759 1605)8 L
()0(Sponsor: X3J11)8 L
()0(Date: 1996-09-13)8 L
()0(Proposal Category:)8 L
()0(__ Editorial change/non-normative contribution)11 L
()0(__ Correction)11 L
()0(X_ New feature)11 L
()0(__ Addition to obsolescent feature list)11 L
()0(__ Addition to Future Directions)11 L
()0(__ Other \(please specify\)  ______________________________)11 L
()0(Area of Standard Affected:)8 L
()0(__ Environment)11 L
()0(X_ Language)11 L
()0(__ Preprocessor)11 L
()0(__ Library)11 L
()0(__ Macro/typedef/tag name)14 L
()0(__ Function)14 L
()0(__ Header)14 L
()0(Prior Art: "<inttypes.h>" and "long long" proposals.)8 L
()0(Target Audience: C programmers)8 L
()0(Related Documents \(if any\):)8 L
()0(Proposal Attached: X_ Yes __ No, but what's your interest?)8 L
()l
()0(With the inclusion of the "<inttypes.h>" proposal, it is)8 L
()0(possible to provide more numeric types than C's integral)8 L
()0(types: "char", "short", "int", "long", and \(recently\) "long)8 L
()0(long".  For example, an implementation might provide 8-bit)8 L
()0(\("char"\), 16-bit \("short"\), 32-bit \("int" and "long"\),)8 L
()0(48-bit \(no corresponding C type\), 64-bit \("long long"\), and)8 L
()0(128-bit \(no corresponding C type\).  The "<inttypes.h>")8 L
()0(proposal gives access to this compiler ``magic'' tokens via)8 L
()0(macros defined in "<inttypes.h>".  This proposal simplifies)8 L
()0(the promotion rules while allowing as many integral types as)8 L
()0(the implementor desires.)8 L
()l
()0(PROPOSED WORDING CHANGES)8 L
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()0(In subclause 6.2.1.5, Usual arithmetic conversions, replace)8 L
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()0(have type "int".'' with the following text:)8 L
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()0(The signedness \(footnote 1\) and precision \(footnote)16 L
()0(2\) is determined for both operands.  Operands with)16 L
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()0(ISO/JTC1/SC22/WG14/N606    Page 2)8 L
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()0(type of the operand with the larger precision.  For)16 L
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()0(types, the C types shall be ordered from largest to)16 L
()0(smallest: signed and unsigned "long long", signed)16 L
()0(and unsigned "long", signed and unsigned "int".  The)16 L
()0(result shall be unsigned if the operands differ in)16 L
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()0(signedness of the operands.)16 L
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()0("int" have the same number of bits available for)16 L
()0(storage, but their range of values differs.)16 L
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()l
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()0(ISO/JTC1/SC22/WG14/N609    Page 1)8 L
()l
()l
()0(Document Number:  WG14 N609/X3J11 96-073)28 L
()l
()l
()0(C9X Revision Proposal)32 L
()0(=====================)32 L
()l
()0(Title: Boolean as a new type)8 L
()0(Author: Frank Farance)8 L
()0(Author Affiliation: Farance Inc.)8 L
()0(Postal Address: 555 Main Street, New York, NY, 10044-0150, USA)8 L
()0(E-mail Address: [email protected])8 L
()0(Telephone Number: +1 212 486 4700)8 L
()0(Fax Number: +1 212 759 1605)8 L
()0(Sponsor: X3J11)8 L
()0(Date: 1996-09-13)8 L
()0(Proposal Category:)8 L
()0(__ Editorial change/non-normative contribution)11 L
()0(__ Correction)11 L
()0(X_ New feature)11 L
()0(__ Addition to obsolescent feature list)11 L
()0(__ Addition to Future Directions)11 L
()0(__ Other \(please specify\)  ______________________________)11 L
()0(Area of Standard Affected:)8 L
()0(__ Environment)11 L
()0(X_ Language)11 L
()0(__ Preprocessor)11 L
()0(__ Library)11 L
()0(__ Macro/typedef/tag name)14 L
()0(__ Function)14 L
()0(__ Header)14 L
()0(Prior Art: C++)8 L
()0(Target Audience: C programmers)8 L
()0(Related Documents \(if any\):)8 L
()0(Proposal Attached: X_ Yes __ No, but what's your interest?)8 L
()l
()0(This proposal is for adding boolean as a new type, not just)8 L
()0(a macro for an existing integer type.  The following)8 L
()0(problems need to be resolved with a boolean type:)8 L
()l
()0(1.  It is a keyword, or hidden magic turned on by)16 L
()0(including a header?)16 L
()l
()0(2.  What is its type?  A new C type or an existing)16 L
()0(one?)16 L
()l
()0(3.  What are the promotion rules?)16 L
()l
()0(4.  What about use of "false" and "true" in the)16 L
()0(preprocessor?)16 L
()l
()0(5.  What is the migration strategy?)16 L
()l
()0(Answer #1: For compatibility reasons, we need to have a)8 L
()0(header that turns on this feature: "#include <bool.h>".  The)8 L
()0(type is "bool" with values "false" and "true".)8 L
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()0(Answer #2: In previous proposals, the type "bool" was a)8 L
()0(macro \(or typedef\) for an existing C integral type.  This)8 L
()0(has raised some issues with respect to promotion rules for)8 L
()0(certain scenarios.  I propose that we make "bool" a real,)8 L
()0(separate C type.)8 L
()l
()0(Answer #3: Promotion from "bool" to other types produces the)8 L
()0(values 0 or 1.  Demotion from other types to bool follows)8 L
()0(the rules: equal to 0 ==> false, not equal to 0 ==> true.)8 L
()l
()0(Answer #4: The macros "false" and "true" will equate to 0)8 L
()0(and 1 respectively.)8 L
()l
()0(Answer #5: The header "<bool.h>" will be used to avoid)8 L
()0(breaking existing programs.  The macro)8 L
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()0(__bool_true_false_are_defined)16 L
()l
()0(will be defined when the implementation defines \(as macros)8 L
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()0(header.  We should indicate that it is our intent to make)8 L
()0("bool" a keyword in the next revision of the Standard.)8 L
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Frank Farance, Farance Inc.   E-mail: [email protected]
Telephone: +1 212 486 4700    FAX: +1 212 759 1605
ISO JTC1/SC22/WG14 & ANSI X3J11 (C Programming Language) Project Editor