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Recurrent Standard C++ quotes

This is a list of quotes from the C++ standard that are often useful while answering questions on StackOverflow. Feel free to suggest quotes that should be added.

The following quotes refer to the N3936 draft (~C++14).


§1.9/15 Program execution [intro.execution]

Except where noted, evaluations of operands of individual operators and of subexpressions of individual expressions are unsequenced. [ Note: In an expression that is evaluated more than once during the execution of a program, unsequenced and indeterminately sequenced evaluations of its subexpressions need not be performed consistently in different evaluations. — end note ] The value computations of the operands of an operator are sequenced before the value computation of the result of the operator. If a side effect on a scalar object is unsequenced relative to either another side effect on the same scalar object or a value computation using the value of the same scalar object, and they are not potentially concurrent (1.10), the behavior is undefined.


§3.9.1/1 Fundamental types [basic.fundamental]

Objects declared as characters (char) shall be large enough to store any member of the implementation’s basic character set. If a character from this set is stored in a character object, the integral value of that character object is equal to the value of the single character literal form of that character. It is implementation-defined whether a char object can hold negative values. Characters can be explicitly declared unsigned or signed. Plain char, signed char, and unsigned char are three distinct types, collectively called narrow character types. A char, a signed char, and an unsigned char occupy the same amount of storage and have the same alignment requirements (3.11); that is, they have the same object representation. For narrow character types, all bits of the object representation participate in the value representation. For unsigned narrow character types, all possible bit patterns of the value representation represent numbers. These requirements do not hold for other types. In any particular implementation, a plain char object can take on either the same values as a signed char or an unsigned char; which one is implementation-defined. For each value i of type unsigned char in the range 0 to 255 inclusive, there exists a value j of type char such that the result of an integral conversion (4.7) from i to char is j, and the result of an integral conversion from j to unsigned char is i.

§8.3.2/4 References [dcl.ref]

It is unspecified whether or not a reference requires storage (3.7).


§17.6.4.2.1/1 Namespace std [namespace.std]

The behavior of a C++ program is undefined if it adds declarations or definitions to namespace std or to a namespace within namespace std unless otherwise specified. A program may add a template specialization for any standard library template to namespace std only if the declaration depends on a user-defined type and the specialization meets the standard library requirements for the original template and is not explicitly prohibited.


§17.6.5.15/1 Moved-from state of library types [lib.types.movedfrom]

Objects of types defined in the C++ standard library may be moved from (12.8). Move operations may be explicitly specified or implicitly generated. Unless otherwise specified, such moved-from objects shall be placed in a valid but unspecified state.


§23.2.2/2 Sequence containers [sequence.reqmts]

The sequence containers offer the programmer different complexity trade-offs and should be used accordingly. vector or array is the type of sequence container that should be used by default. list or forward_list should be used when there are frequent insertions and deletions from the middle of the sequence. deque is the data structure of choice when most insertions and deletions take place at the beginning or at the end of the sequence.

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