value initialization
De cppreference.com
 |
This page has been machine-translated from the English version of the wiki using Google Translate.
The translation may contain errors and awkward wording. Hover over text to see the original version. You can help to fix errors and improve the translation. For instructions click here. |
Proporciona el valor inicial por defecto a un objeto nuevo .
Original:
Provides the default initial value to a new object.
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
You can help to correct and verify the translation. Click here for instructions.
Contenido |
[editar] Sintaxis
T object {};
|
(1) | (desde C++11) | |||||||
T();
T |
(2) | (desde C++11) | |||||||
new T ();
|
(3) | (desde C++11) | |||||||
[editar] Explicación
Valor de inicialización se realiza en tres situaciones:
Original:
Value initialization is performed in three situations:
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
You can help to correct and verify the translation. Click here for instructions.
1)
cuando una variable llamada (automático, estático, hilo o local-) se declara con el inicializador consiste en un par de llaves. (desde C++11)
Original:
when a named variable (automatic, static, or thread-local) is declared with the initializer consisting of a pair of braces. (desde C++11)
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
You can help to correct and verify the translation. Click here for instructions.
2)
cuando un objeto temporal sin nombre se crea con el inicializador que consiste en un par de paréntesis vacíos o los apoyos .
Original:
when a nameless temporary object is created with the initializer consisting of an empty pair of parentheses or braces.
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
You can help to correct and verify the translation. Click here for instructions.
3)
cuando un objeto con una duración de almacenamiento dinámico es creado por una nueva-expresión con el inicializador que consiste en un par vacío de paréntesis o llaves .
Original:
when an object with dynamic storage duration is created by a new-expression with the initializer consisting of an empty pair of parentheses or braces.
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
You can help to correct and verify the translation. Click here for instructions.
Los efectos de la inicialización de valor son:
Original:
The effects of value initialization are:
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
You can help to correct and verify the translation. Click here for instructions.
- Si
Tes un tipo de clase con al menos un constructor proporcionado por el usuario de cualquier clase, la default constructor se llama .Original:IfTis a class type with at least one user-provided constructor of any kind, the default constructor is called.The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
- Si
Tes un tipo de clase no-unión sin ningún constructor proporcionados por el usuario, el objeto es inicializarse en cero y luego el constructor por defecto declarado implícitamente-es llamado (a menos que sea trivial)Original:IfTis an non-union class type without any user-provided constructors, then the object is inicializarse en cero and then the implicitly-declared default constructor is called (unless it's trivial)The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
- Si
Tes un tipo de matriz, cada elemento de la matriz es el valor inicializadoOriginal:IfTis an array type, each element of the array is value-initializedThe text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
- De lo contrario, el objeto es inicializarse en cero .Original:Otherwise, the object is zero-initialized.The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
[editar] Notas
La sintaxis T object(); no inicializa un objeto, sino que declara una función que no tiene argumentos y
T devoluciones. La forma de valor inicializar una variable llamada antes de C + 11 fue T object = T();, que inicializa un valor temporal y luego copia a inicializar el objeto: .. la mayoría de los compiladores de optimizar la copia en este casoOriginal:
The syntax T object(); does not initialize an object; it declares a function that takes no arguments and returns
T. The way to value-initialize a named variable before C++11 was T object = T();, which value-initializes a temporary and then copy-initializes the object: most compilers optimize out the copy in this case.The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
You can help to correct and verify the translation. Click here for instructions.
Las referencias no pueden ser de valor inicializado .
Original:
References cannot be value-initialized.
The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
You can help to correct and verify the translation. Click here for instructions.
Todos los contenedores estándar (std::vector, std::list, etc) de valor inicializar sus elementos cuando se construye con un argumento
size_type sola o cuando se cultivan por una llamada a resize() .Original:
All standard containers (std::vector, std::list, etc) value-initialize their elements when constructed with a single
size_type argument or when grown by a call to resize().The text has been machine-translated via Google Translate.
You can help to correct and verify the translation. Click here for instructions.
You can help to correct and verify the translation. Click here for instructions.
[editar] Ejemplo
#include <string> #include <vector> #include <iostream> struct T1 { int mem1; std::string mem2; }; // no constructors struct T2 { int mem1; std::string mem2; T2(const T2&) {} // a constructor, but no default }; struct T3 { int mem1; std::string mem2; T3() {} // user-provided default ctor }; std::string s{}; // calls default ctor, the value is "" (empty string) int main() { int n{}; // non-class value-initialization, value is 0 double f = double(); // non-class value-init, value is 0.0 int* a = new int[10](); // array of 10 zeroes T1 t1{}; // no ctors: zero-initialized // t1.mem1 is zero-initialized // t1.mem2 is default-initialized // T2 t2{}; // error: has a ctor, but no default ctor T3 t3{}; // user-defined default ctor: // t3.mem1 is default-initialized (the value is indeterminate) // t3.mem2 is default-initialized std::vector<int> v(3); // value-initializes three ints std::cout << s.size() << ' ' << n << ' ' << f << ' ' << a[9] << ' ' << v[2] << '\n'; std::cout << t1.mem1 << ' ' << t3.mem1 << '\n'; delete[] a; }
Output:
0 0 0 0 0 0 4199376
