Difference between revisions of "cpp/language/attributes/indeterminate"
(Added indeterminate, which is introduced by P2795R5 (Erroneous behaviour for uninitialized reads).) |
m (→Explanation: +link to IFNDR.) |
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{{attr|indeterminate}} can be applied to the definition of a block variable with automatic {{lt|cpp/language/storage duration}} or to a declaration of a parameter of a [[cpp/language/function|function declaration]]. The attribute specifies that the bytes comprising the storage of an object with automatic storage duration is initially [[cpp/language/default initialization#Indeterminate and erroneous values|indeterminate]] rather than erroneous. | {{attr|indeterminate}} can be applied to the definition of a block variable with automatic {{lt|cpp/language/storage duration}} or to a declaration of a parameter of a [[cpp/language/function|function declaration]]. The attribute specifies that the bytes comprising the storage of an object with automatic storage duration is initially [[cpp/language/default initialization#Indeterminate and erroneous values|indeterminate]] rather than erroneous. | ||
| − | If a function parameter is declared with {{attr|indeterminate}}, it must be declared in the first declaration of its function. If a function parameter is declared with {{attr|indeterminate}} in the first declaration of its function in one translation unit and the same function is declared without {{attr|indeterminate}} on the same parameter in its first declaration in another translation unit, the program is ill-formed, no diagnostic required. | + | If a function parameter is declared with {{attr|indeterminate}}, it must be declared in the first declaration of its function. If a function parameter is declared with {{attr|indeterminate}} in the first declaration of its function in one translation unit and the same function is declared without {{attr|indeterminate}} on the same parameter in its first declaration in another translation unit, the program is [[cpp/language/ub#Explanation|ill-formed, no diagnostic required]]. |
===Example=== | ===Example=== | ||
Revision as of 06:14, 23 April 2024
Indicates that the variable or function parameter has an indeterminate value if it is not initialized.
Syntax
[[indeterminate]]
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Explanation
[[indeterminate]] can be applied to the definition of a block variable with automatic storage duration or to a declaration of a parameter of a function declaration. The attribute specifies that the bytes comprising the storage of an object with automatic storage duration is initially indeterminate rather than erroneous.
If a function parameter is declared with [[indeterminate]], it must be declared in the first declaration of its function. If a function parameter is declared with [[indeterminate]] in the first declaration of its function in one translation unit and the same function is declared without [[indeterminate]] on the same parameter in its first declaration in another translation unit, the program is ill-formed, no diagnostic required.
Example
void f(int); void g() { int x [[indeterminate]]; // indeterminate value int y; // erroneous value f(x); // undefined behavior f(y); // erroneous behavior } struct T { T() {} int x; }; void h(T a [[indeterminate]], T b) { f(a.x); // undefined behavior when called below f(b.x); // erroneous behavior when called below } h(T(), T());
