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34
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Semantics, Pre/Post-conditions
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Key English Chinese (Simplified Han script) Actions
File
文件
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.
[*File] 概念抽象了对底层文件系统中文件的访问。为了支持其他平台接口，用户可以编写满足这些要求的自有 [*File] 类型。
Associated Types
关联类型
* [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
要求
In this table:
在下表中：
* `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` 是一个 [*File] 类型。
* `f` 是 `F` 的一个实例。
* `p` 是一个 `char const*` 类型的值，指向一个空字符（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` 是一个 [link beast.ref.boost__beast__file_mode `file_mode`] 的实例。
* `n` 是字节数，可转换为 `std::size_t` 类型。
* `o` 是文件中的字节偏移量，可转换为 `std::uint64_t` 类型。
* `b` 是指向内存的任意非常量指针。
* `c` 是指向内存的任意可能为常量的指针。
* `ec` 是一个 [link beast.ref.boost__beast__error_code `error_code`] 类型的引用。
Valid expressions
有效表达式
Expression
表达式
Type
类型
34
Semantics, Pre/Post-conditions
 
Operation
操作
Return Type
返回类型
`F()`
`F()`
Default constructable
默认构造（Default constructible）
`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.
可析构。若 `f` 引用一个打开的文件，则先将其关闭，其行为等同于调用 `close`，且忽略可能产生的错误。
`f.is_open()`
`f.is_open()`
`bool`
`bool`
Returns `true` if `f` refers to an open file, `false` otherwise.
若 `f` 引用一个打开的文件，则返回 `true`，否则返回 `false`。
`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.
若 `f` 引用一个打开的文件，此函数将尝试将其关闭。无论关闭过程中是否发生错误，后续对 `f.is_open()` 的调用均会返回 `false`。同时，该函数会根据实际执行情况设置错误代码：若未发生错误，则确保 `!ec` 为 `true`；若发生错误，则将其设置为相应的错误代码。
`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.
该函数尝试以 `m` 指定的模式打开 `p` 指定的路径对应的文件。若 `f` 引用一个打开的文件，则先将其关闭，其行为等同于调用 `close`，且忽略可能产生的错误。若打开成功，后续对 `f.is_open()` 的调用均会返回 `true`。同时，该函数会根据实际执行情况设置错误代码：若未发生错误，则确保 `!ec` 为 `true`；若发生错误，则将其设置为相应的错误代码。
`f.size(ec)`
`f.size(ec)`
34
`std::uint64_t`
 
Key English Chinese (Simplified Han script) Actions
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.
该函数尝试从 `f` 引用的打开文件中，自当前文件偏移量处读取 `n` 个字节。读取的字节将存储到地址 `b` 处的内存缓冲区中，该缓冲区的大小必须至少为 `n` 个字节。该函数会将文件偏移量推进已读取的字节数，并返回实际读取的字节数，该值可能小于 `n`。若 `f` 未引用一个打开的文件，该函数会将 `ec` 设置为 `errc::invalid_argument` 并立即返回。同时，该函数会根据实际执行情况设置错误代码：若未发生错误，则确保 `!ec` 为 `true`；若发生错误，则将其设置为相应的错误代码。若在读取任何字节之前检测到文件结束条件，该函数将确保 `!ec` 为 `true`，且返回值为 0。
`f.write(c,n,ec)`
`f.write(c,n,ec)`
Exemplar
示例
`f.is_open()`
`f.is_open()`
`bool`
`bool`
Returns `true` if `f` refers to an open file, `false` otherwise.
若 `f` 引用一个打开的文件，则返回 `true`，否则返回 `false`。
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.
若 `f` 引用一个打开的文件，此函数将尝试将其关闭。无论关闭过程中是否发生错误，后续对 `f.is_open()` 的调用均会返回 `false`。同时，该函数会根据实际执行情况设置错误代码：若未发生错误，则确保 `!ec` 为 `true`；若发生错误，则将其设置为相应的错误代码。
* `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` 是一个 [*File] 类型。
* `f` 是 `F` 的一个实例。
* `p` 是一个 `char const*` 类型的值，指向一个空字符（null）
`f.~F()`
`f.~F()`
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.
该函数尝试以 `m` 指定的模式打开 `p` 指定的路径对应的文件。若 `f` 引用一个打开的文件，则先将其关闭，其行为等同于调用 `close`，且忽略可能产生的错误。若打开成功，后续对 `f.is_open()` 的调用均会返回 `true`。同时，该函数会根据实际执行情况设置错误代码：若未发生错误，则确保 `!ec` 为 `true`；若发生错误，则将其设置为相应的错误代码。
If `f` refers to an open file, this function attempts to determine the file size and return its value. If `f` does not refer to an open file, the function will set `ec` to `errc::invalid_argument` and return 0. The function will ensure that `!ec` is `true` if there was no error or set to the appropriate error code if an error occurred.
若 `f` 引用一个打开的文件，该函数将尝试获取并返回其文件大小。若 `f` 未引用一个打开的文件，该函数会将 `ec` 设置为 `errc::invalid_argument` 并返回 0。同时，该函数会根据实际执行情况设置错误代码：若未发生错误，则确保 `!ec` 为 `true`；若发生错误，则将其设置为相应的错误代码。
If `f` refers to an open file, this function attempts to determine the current file offset and return it. If `f` does not refer to an open file, the function will set `ec` to `errc::invalid_argument` and return 0. The function will ensure that `!ec` is `true` if there was no error or set to the appropriate error code if an error occurred.
若 `f` 引用一个打开的文件，该函数将尝试获取并返回当前文件偏移量。若 `f` 未引用一个打开的文件，该函数会将 `ec` 设置为 `errc::invalid_argument` 并返回 0。同时，该函数会根据实际执行情况设置错误代码：若未发生错误，则确保 `!ec` 为 `true`；若发生错误，则将其设置为相应的错误代码。
Attempts to reposition the current file offset to the value `o`, which represents a byte offset relative to the beginning of the file. 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.
该函数尝试将当前文件偏移量重新定位到 `o`，该值表示相对于文件起始位置的字节偏移量。若 `f` 未引用一个打开的文件，该函数会将 `ec` 设置为 `errc::invalid_argument` 并立即返回。同时，该函数会根据实际执行情况设置错误代码：若未发生错误，则确保 `!ec` 为 `true`；若发生错误，则将其设置为相应的错误代码。
`f.read(b,n,ec)`
`f.read(b,n,ec)`
34
`std::size_t`
 
34
Semantics, Pre/Post-conditions
 
34
`std::uint64_t`
 

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String updated in the repository
Semantics, Pre/Post-conditions
语义，前置/后置条件
34
06/26/2026
User avatar Bstran

Translation added
Semantics, Pre/Post-conditions
语义，前置/后置条件
34
06/18/2026
User avatar admin

String added in the repository
Semantics, Pre/Post-conditions
 
34
06/05/2026
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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
06/26/2026
Source string age
06/05/2026
Translation file QuickBook file
doc/qbk/07_concepts/File_zh_Hans.qbk, string 12