Jones D.M.The new C standard (C90 and C++).An economic and cultural commentary.2005

914 If the characters ’, \, ", //, or /* occur in the sequence between the < and > delimiters, the behavior is undefined.

C90

The character sequence // was not specified as causing undefined behavior in C90 (which did not treat this sequence as the start of a comment).

915 Similarly, if the characters ’, \, //, or /* occur in the sequence between the " delimiters, the behavior is undefined. 69)

C90

The character sequence // was not specified as causing undefined behavior in C90 (which did not treat this sequence as the start of a comment).

918 A header name preprocessing token is recognized only within a #include preprocessing directive.

C90

This statement summarizes the response to DR #017q39 against the C90 Standard.

C++

The C++ Standard contains the same wording as the C90 Standard.

6.4.8 Preprocessing numbers

921

pp-number:

digit

. digit pp-number digit

pp-number identifier-nondigit pp-number e sign

pp-number E sign pp-number p sign pp-number P sign pp-number .

characters between < and >delimiters

header name recognized

within #include

pp-number syntax

934 Between the previous and next sequence point an object shall have its stored value modified at most once by the evaluation of an expression.

C++

Between the previous and next sequence point a scalar object shall have its stored value modified at most once by the evaluation of an expression.

The C++ Standard avoids any ambiguity in the interpretation of object by specifying scalar type.

938 Some operators (the unary operator ~, and the binary operators <<, >>, &, ^, and |, collectively described as bitwise operators) are required to have operands that have integer type.

object

modified once between sequence points

5p4

bitwise operators

exception condition

C++

These operators exhibit the same range of behaviors in C++. This is called out within the individual descriptions of each operator in the C++ Standard.

If an exceptional condition occurs during the evaluation of an expression (that is, if the result is not mathe- 940 matically defined or not in the range of representable values for its type), the behavior is undefined.

malloc function

The term effective type is not defined in C ++. A type needs to be specified when the C ++ new operator is used. However, the C++ Standard includes the C library, so it is possible to allocate storage via a call to the malloc library function, which does not associate a type with the allocated storage.

In the C90 Standard the term used in the following types was derived type. The term effective type is new in the C99 Standard and is used throughout the same list.

953 — a type compatible with the effective type of the object,

C++

— the dynamic type of the object,

the type of the most derived object (1.8) to which the lvalue denoted by an lvalue expression refers. [Example: if a pointer (8.3.1) p whose static type is “pointer to class B” is pointing to an object of class D, derived from B (clause 10), the dynamic type of the expression *p is “ D.” References (8.3.2) are treated similarly. ] The dynamic type of an rvalue expression is its static type.

The difference between an object’s dynamic and static type only has meaning in C++.

Use of effective type means that C gives types to some objects that have no type in C++. C++ requires the types to be the same, while C only requires that the types be compatible. However, the only difference occurs when an enumerated type and its compatible integer type are intermixed.

958 — a character type.

object

stored value accessed only by

3.10p15

1.3.3 dynamic type

627 compatible type if

The C++ Standard does not explicitly specify support for the character type signed char. However, it does specify that the type char may have the same representation and range of values as signed char (or unsigned char).

It is common practice to access the subcomponents of an object using a char or unsigned char type. However, there is code that uses signed char, and it would be a brave vendor whose implementation did not assume that objects having type signed char were not a legitimate alias for accesses to any object.

513 char range, repre-

sentation and behavior

footnote 76

primaryexpression syntax

The contraction of expressions is not explicitly discussed in the C++ Standard.

76) This license is specifically intended to allow implementations to exploit fast machine instructions that 965 combine multiple C operators.

C90

Such instructions were available in processors that existed before the creation of the C90 Standard and there were implementations that made use of them. However, this license was not explicitly specified in the C90 Standard.

C++

The C++ Standard contains no such explicit license.

6.5.1 Primary expressions

967

primary-expression: identifier constant string-literal

( expression )

C++

array

n-dimensional reference

If E is an n-dimensional array (n≥2) with dimensions i×j×· · ·×k then E (used as other than an lvalue) is 984 converted to a pointer to an (n-1)-dimensional array with dimensions j×· · ·×k

C++

function call arguments agree

with parameters

If the expression that denotes the called function has a type that includes a prototype, the number of argu- 990 ments shall agree with the number of parameters.

C++

5.2.2p6

argument type may be assigned

A function can be declared to accept fewer arguments (by declaring default arguments (8.3.6)) or more arguments (by using the ellipsis, ... 8.3.5) than the number of parameters in the function definition (8.4). [Note: this implies that, except where the ellipsis (...) is used, a parameter is available for each argument. ]

A called function in C++, whose definition uses the syntax specified in standard C, has the same restrictions placed on it by the C++ Standard as those in C.

Each argument shall have a type such that its value may be assigned to an object with the unqualified version 991 of the type of its corresponding parameter.

992 A postfix expression followed by parentheses () containing a possibly empty, comma-separated list of expressions is a function call.

C90

The C90 Standard included the requirement:

If the expression that precedes the parenthesized argument list in a function call consists solely of an identifier, and if no declaration is visible for this identifier, the identifier is implicitly declared exactly as if, in the innermost block containing the function call, the declaration

extern int identifier();

appeared.

operator ()