Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>The informations on the left shift operator in C99 draft standard (ISO/IEC9899:TC3, aka WG14/N1256) are rather scant.</p> <p>Section 6.5.7 (bitwise shift operators) has already been cited by Alter Mann. </p> <p>Annex J, section J.2 (Undefined behavior) says the following:</p> <blockquote> <p>The behavior is undefined in the following circumstances:<br/> [...]</p> <p>— An expression is shifted by a negative number or by an amount greater than or equal to the width of the promoted expression (6.5.7).</p> <p>— An expression having signed promoted type is left-shifted and either the value of the expression is negative or the result of shifting would be not be representable in the promoted type (6.5.7).</p> </blockquote> <p>I don't think it is allowed for a conforming implementation to make some mandatory undefined behavior defined. If I'm not mistaken an implementation is allowed to define <strong>unspecified behavior</strong> (but it is not required to) and is required to specify <strong>implementation defined behavior</strong>, but undefined behavior cannot be <em>specified</em>. This doesn't mean that an implementation cannot choose a <em>sane meaningful behavior</em>, but it cannot let the user rely on that (it cannot "specify it").</p> <p>I admit I'm not completely sure of that. Hope this helps.</p> <p><strong>Edit:</strong> Upon further reflection I think a conforming implementation <em>can specify</em> a behavior for what the standard deems <strong>undefined behavior</strong>, but the resulting program cannot be called conforming (see section 3.4.3).</p>
    singulars
    1. This table or related slice is empty.
    1. POWhat aspects of signed left shift are undefined with GCC?
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USLorenzo Donati
    1. USLorenzo Donati
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. COFor an example of undefined behavior that was always intended to be (and routinely is) defined by compilers, an unknown `%` sequence in a `printf()` format string is undefined behavior.
      singulars
      1. PO
      1. USPascal Cuoq
    2. COSo if an implementation specifies a defined behavior, where it is required to specify undefined behavior, that implementation is exhibiting undefined behavior? Kafkaesque...
      singulars
      1. PO
      1. USBrett Hale
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload