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std::fread

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< cpp‎ | io‎ | c

 
 
Entrada / salida de la biblioteca
I / O manipuladores
C-estilo I / O
Buffers
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Buffers
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basic_streambuf
basic_filebuf
basic_stringbuf
strstreambuf(obsoleto)
Arroyos
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Streams
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Abstracciones
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Abstractions
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ios_base
basic_ios
basic_istream
basic_ostream
basic_iostream
File I / O
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File I/O
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basic_ifstream
basic_ofstream
basic_fstream
Cadena de I / O
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String I/O
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basic_istringstream
basic_ostringstream
basic_stringstream
Matriz I / O
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Array I/O
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istrstream(obsoleto)
ostrstream(obsoleto)
strstream(obsoleto)
Tipos
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Types
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streamoff
streamsize
fpos
Error interfaz categoría
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Error category interface
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iostream_category(C++11)
io_errc(C++11)
 
C-estilo I / O
Funciones
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Functions
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Acceso a archivos
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File access
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Directo de entrada / salida
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Direct input/output
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fread
fwrite
Entrada sin formato / salida
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Unformatted input/output
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Formato de entrada / salida
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Formatted input/output
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Presentar posicionamiento
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File positioning
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ftell
fgetpos
fseek
fsetpos
rewind
Gestión de errores
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Error handling
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clearerr
feof
ferror
perror
Las operaciones en los archivos
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Operations on files
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remove
rename
tmpfile
tmpnam
 
Defined in header <cstdio>
std::size_t fread( void* buffer, std::size_t size, std::size_t count, std::FILE* stream );
Lee hasta objetos count en el buffer matriz a partir de la corriente de entrada dado stream como si llamando std::fgetc size veces para cada objeto, y el almacenamiento de los resultados, en el orden obtenido en las sucesivas posiciones de buffer, que se reinterpreta como una matriz de unsigned char. El indicador de posición de fichero para el flujo se hace avanzar por el número de caracteres leídos .
Original:
Reads up to count objects into the array buffer from the given input stream stream as if by calling std::fgetc size times for each object, and storing the results, in the order obtained, into the successive positions of buffer, which is reinterpreted as an array of unsigned char. The file position indicator for the stream is advanced by the number of characters read.
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Si los objetos no son TriviallyCopyable, el comportamiento no está definido .
Original:
If the objects are not TriviallyCopyable, the behavior is undefined.
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Si se produce un error, el valor resultante del indicador de posición del fichero para el flujo es
Original:
If an error occurs, the resulting value of the file position indicator for the stream is
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indeterminada. Si un elemento parcial es leído, su valor es indeterminado
Original:
indeterminate. If a partial element is read, its value is indeterminate
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Contenido

[editar] Parámetros

buffer -
puntero hacia el objeto primero de la matriz para ser leído
Original:
pointer to the first object in the array to be read
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size -
tamaño de cada objeto en bytes
Original:
size of each object in bytes
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count -
el número de los objetos que se deben leer
Original:
the number of the objects to be read
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[editar] Valor de retorno

Número de objetos leídos con éxito, lo que puede ser inferior a count si una condición de error o de fin de archivo se produce .
Original:
Number of objects read successfully, which may be less than count if an error or end-of-file condition occurs.
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Si size o count es cero, fread devuelve cero y no realiza ninguna otra acción .
Original:
If size or count is zero, fread returns zero and performs no other action.
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[editar] Ejemplo

#include <iostream>
#include <cstdio>
#include <fstream>
#include <vector>
int main()
{
    // prepare file
    std::ofstream("test.txt") << 1 << ' ' << 2 << '\n';
    std::FILE* f = std::fopen("test.txt", "r");
 
    std::vector<char> buf(4); // char is trivally copyable
    std::fread(&buf[0], sizeof buf[0], buf.size(), f);
 
    for(char n : buf)
        std::cout << n;
 
    std::vector<std::string> buf2; // string is not trivially copyable
// this would result in undefined behavior
//    std::fread(&buf2[0], sizeof buf2[0], buf2.size(), f);
}

Output:

1 2

[editar] Ver también

lee la entrada con formato desde stdin, una secuencia de archivo o un tampón
Original:
reads formatted input from stdin, a file stream or a buffer
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(función) [edit]
recibe una cadena de caracteres a partir de una secuencia de archivo
Original:
gets a character string from a file stream
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(función) [edit]
escribe en un archivo
Original:
writes to a file
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(función) [edit]
C documentation for fread