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type: table cell
34
English
Semantics, Pre/Post-conditions
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Key English Chinese (Simplified Han script) Actions
File
File
The [*File] concept abstracts access to files in the underlying file system. To support other platform interfaces, users may author their own [*File] types which meet these requirements.
The [*File] concept abstracts access to files in the underlying file system. To support other platform interfaces, users may author their own [*File] types which meet these requirements.
Associated Types
Associated Types
* [link beast.ref.boost__beast__file_mode `file_mode`]
* [link beast.ref.boost__beast__is_file `is_file`]
* [link beast.ref.boost__beast__file_mode `file_mode`]
* [link beast.ref.boost__beast__is_file `is_file`]
Requirements
Requirements
In this table:
In this table:
* `F` is a [*File] type
* `f` is an instance of `F`
* `p` is a value of type `char const*` which points to a null
* `F` is a [*File] type
* `f` is an instance of `F`
* `p` is a value of type `char const*` which points to a null
* `m` is an instance of [link beast.ref.boost__beast__file_mode `file_mode`]
* `n` is a number of bytes, convertible to `std::size_t`
* `o` is a byte offset in the file, convertible to `std::uint64_t`
* `b` is any non-const pointer to memory
* `c` is any possibly-const pointer to memory
* `ec` is a reference of type [link beast.ref.boost__beast__error_code `error_code`]
* `m` is an instance of [link beast.ref.boost__beast__file_mode `file_mode`]
* `n` is a number of bytes, convertible to `std::size_t`
* `o` is a byte offset in the file, convertible to `std::uint64_t`
* `b` is any non-const pointer to memory
* `c` is any possibly-const pointer to memory
* `ec` is a reference of type [link beast.ref.boost__beast__error_code `error_code`]
Valid expressions
Valid expressions
Expression
Expression
Type
Type
34
Semantics, Pre/Post-conditions
 
Operation
Operation
Return Type
Return Type
`F()`
`F()`
Default constructable
Default constructable
`f.~F()`
`f.~F()`
Destructible. If `f` refers to an open file, it is first closed as if by a call to `close` with the error ignored.
Destructible. If `f` refers to an open file, it is first closed as if by a call to `close` with the error ignored.
`f.is_open()`
`f.is_open()`
`bool`
`bool`
Returns `true` if `f` refers to an open file, `false` otherwise.
Returns `true` if `f` refers to an open file, `false` otherwise.
`f.close(ec)`
`f.close(ec)`
If `f` refers to an open file, this function attempts to close the file. Regardless of whether an error occurs or not, a subsequent call to `f.is_open()` will return `false`. The function will ensure that `!ec` is `true` if there was no error or set to the appropriate error code if an error occurred.
If `f` refers to an open file, this function attempts to close the file. Regardless of whether an error occurs or not, a subsequent call to `f.is_open()` will return `false`. The function will ensure that `!ec` is `true` if there was no error or set to the appropriate error code if an error occurred.
`f.open(p,m,ec)`
`f.open(p,m,ec)`
Attempts to open the file at the path specified by `p` with the mode specified by `m`. Upon success, a subsequent call to `f.is_open()` will return `true`. If `f` refers to an open file, it is first closed as if by a call to `close` with the error ignored. The function will ensure that `!ec` is `true` if there was no error or set to the appropriate error code if an error occurred.
Attempts to open the file at the path specified by `p` with the mode specified by `m`. Upon success, a subsequent call to `f.is_open()` will return `true`. If `f` refers to an open file, it is first closed as if by a call to `close` with the error ignored. The function will ensure that `!ec` is `true` if there was no error or set to the appropriate error code if an error occurred.
`f.size(ec)`
`f.size(ec)`
34
`std::uint64_t`
 
Key English Chinese (Simplified Han script) Actions
Attempts to write `n` bytes from the buffer pointed to by `c` to the current file offset of the open file referred to by `f`. The memory buffer at `c` must point to storage of at least `n` bytes meant to be copied to the file. The function advances the file offset by the amount written, and returns the number of bytes actually written, which may be less than `n`. If `f` does not refer to an open file, the function will set `ec` to `errc::invalid_argument` and return immediately. The function will ensure that `!ec` is `true` if there was no error or set to the appropriate error code if an error occurred.
Attempts to write `n` bytes from the buffer pointed to by `c` to the current file offset of the open file referred to by `f`. The memory buffer at `c` must point to storage of at least `n` bytes meant to be copied to the file. The function advances the file offset by the amount written, and returns the number of bytes actually written, which may be less than `n`. If `f` does not refer to an open file, the function will set `ec` to `errc::invalid_argument` and return immediately. The function will ensure that `!ec` is `true` if there was no error or set to the appropriate error code if an error occurred.
Destructible. If `f` refers to an open file, it is first closed as if by a call to `close` with the error ignored.
Destructible. If `f` refers to an open file, it is first closed as if by a call to `close` with the error ignored.
Attempts to read `n` bytes starting at the current file offset from the open file referred to by `f`. Bytes read are stored in the memory buffer at address `b` which must be at least `n` bytes in size. The function advances the file offset by the amount read, and returns the number of bytes actually read, which may be less than `n`. If `f` does not refer to an open file, the function will set `ec` to `errc::invalid_argument` and return immediately. The function will ensure that `!ec` is `true` if there was no error or set to the appropriate error code if an error occurred. If an end-of-file condition is detected prior to reading any bytes, the function will ensure that `!ec` is `true` and the return value shall be 0.
Attempts to read `n` bytes starting at the current file offset from the open file referred to by `f`. Bytes read are stored in the memory buffer at address `b` which must be at least `n` bytes in size. The function advances the file offset by the amount read, and returns the number of bytes actually read, which may be less than `n`. If `f` does not refer to an open file, the function will set `ec` to `errc::invalid_argument` and return immediately. The function will ensure that `!ec` is `true` if there was no error or set to the appropriate error code if an error occurred. If an end-of-file condition is detected prior to reading any bytes, the function will ensure that `!ec` is `true` and the return value shall be 0.
`f.write(c,n,ec)`
`f.write(c,n,ec)`
* `m` is an instance of [link beast.ref.boost__beast__file_mode `file_mode`]
* `n` is a number of bytes, convertible to `std::size_t`
* `o` is a byte offset in the file, convertible to `std::uint64_t`
* `b` is any non-const pointer to memory
* `c` is any possibly-const pointer to memory
* `ec` is a reference of type [link beast.ref.boost__beast__error_code `error_code`]
* `m` is an instance of [link beast.ref.boost__beast__file_mode `file_mode`]
* `n` is a number of bytes, convertible to `std::size_t`
* `o` is a byte offset in the file, convertible to `std::uint64_t`
* `b` is any non-const pointer to memory
* `c` is any possibly-const pointer to memory
* `ec` is a reference of type [link beast.ref.boost__beast__error_code `error_code`]
Valid expressions
Valid expressions
Expression
Expression
Type
Type
Operation
Operation
Return Type
Return Type
`F()`
`F()`
Default constructable
Default constructable
`f.~F()`
`f.~F()`
34
`std::size_t`
 
34
Semantics, Pre/Post-conditions
 
34
`std::uint64_t`
 

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String added in the repository
Semantics, Pre/Post-conditions
 
34
06/05/2026
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Glossary

English Chinese (Simplified Han script)
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String information

Key
34
Source string description
type: table cell
Unit identifier
58587
Source string location
string ID 34
String age
06/05/2026
Last updated
06/05/2026
Source string age
06/05/2026
Translation file QuickBook file
doc/qbk/07_concepts/File_zh_Hans.qbk, string 12