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std::basic_streambuf::underflow

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< cpp‎ | io‎ | basic streambuf

 
 
Entrada / salida de la biblioteca
I / O manipuladores
C-estilo I / O
Buffers
Original:
Buffers
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(obsoleto)
Arroyos
Original:
Streams
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Abstracciones
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Abstractions
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File I / O
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File I/O
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Cadena de I / O
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String I/O
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Matriz I / O
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Array I/O
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(obsoleto)
(obsoleto)
(obsoleto)
Tipos
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Types
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Error interfaz categoría
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Error category interface
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(C++11)
 
std::basic_streambuf
Las funciones públicas miembros
Original:
Public member functions
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Locales
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Locales
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Posicionamiento
Original:
Positioning
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Obtenga zona
Original:
Get area
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Ponga zona
Original:
Put area
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Dos puntos
Original:
Putback
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Protegido funciones miembro
Original:
Protected member functions
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Locales
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Locales
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Posicionamiento
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Positioning
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Obtenga zona
Original:
Get area
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basic_streambuf::underflow
Ponga zona
Original:
Put area
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Dos puntos
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Putback
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int_type underflow();
Se asegura de que al menos un carácter está disponible en el área de entrada mediante la actualización de los punteros a la zona de entrada (si es necesario). Devuelve el valor de ese carácter en el éxito o en el fracaso traits::eof() .
Original:
Ensures that at least one character is available in the input area by updating the pointers to the input area (if needed). Returns the value of that character on success or traits::eof() on failure.
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La función puede actualizar gptr, egptr y eback punteros para definir la ubicación de los datos recién cargados (si los hay). En caso de fallo, la función se asegura de que sea gptr() == nullptr o gptr() == egptr .
Original:
The function may update gptr, egptr and eback pointers to define the location of newly loaded data (if any). On failure, the function ensures that either gptr() == nullptr or gptr() == egptr.
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La versión de la clase base de la función no hace nada. Las clases derivadas pueden reemplazar esta función para permitir las actualizaciones del área get en el caso de agotamiento .
Original:
The base class version of the function does nothing. The derived classes may override this function to allow updates to the get area in the case of exhaustion.
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Contenido

[editar] Parámetros

(Ninguno)
Original:
(none)
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[editar] Valor de retorno

El valor del carácter al que apunta el puntero del' llegar después de la llamada en caso de éxito, o de lo contrario traits::eof() .
Original:
The value of the character pointed to by the get pointer after the call on success, or traits::eof() otherwise.
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La versión de la clase base de la función llama traits::eof() .
Original:
The base class version of the function calls traits::eof().
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[editar] Nota

Las funciones públicas de std::streambuf llamar a esta función sólo si gptr() == nullptr o gptr() >= egptr() .
Original:
The public functions of std::streambuf call this function only if gptr() == nullptr or gptr() >= egptr().
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[editar] Ejemplo

[editar]
#include <iostream>
#include <sstream>
 
class null_filter_buf : public std::streambuf {
    std::streambuf* src;
    char ch; // single-byte buffer
protected:
    int underflow() {
        while( (ch= src->sbumpc()) == '\0') ; // skip zeroes
        setg(&ch, &ch, &ch+1); // make one read position available
        return ch; // may return EOF
    }
public:
    null_filter_buf(std::streambuf* buf) : src(buf) {
        setg(&ch, &ch+1, &ch+1); // buffer is initially full
    }
};
 
void filtered_read(std::istream& in)
{
    std::streambuf* orig = in.rdbuf();
    null_filter_buf buf(orig);
    in.rdbuf(&buf);
    for(char c; in.get(c); )
            std::cout << c;
    in.rdbuf(orig);
}
 
int main()
{
    char a[] = "This i\0s \0an e\0\0\0xample";
    std::istringstream in(std::string(std::begin(a), std::end(a)));
    filtered_read(in);
}

Salida:

This is an example

[editar] Ver también

[virtual]
lee los caracteres de la secuencia de entrada asociado a la zona de get y avanza el siguiente
Original:
reads characters from the associated input sequence to the get area and advances the next pointer
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(función miembro virtual protegido) [editar]
[virtual]
escribe los caracteres a la secuencia de salida asociado del área de venta
Original:
writes characters to the associated output sequence from the put area
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(función miembro virtual protegido) [editar]