std::basic_ifstream::basic_ifstream

(1) 預設建構函式

Constructs a basic_ifstream object that is not associated with any file.
Internally, its basic_istream base constructor is passed a pointer to a newly constructed basic_filebuf object (the internal file stream buffer).

(2) initialization constructor

Constructs a basic_ifstream object, initially associated with the file identified by its first argument (filename), open with the mode specified by mode.
Internally, its basic_istream base constructor is passed a pointer to a newly constructed basic_filebuf object (the internal file stream buffer). Then, basic_filebuf::open is called with filename and mode as arguments.
如果檔案無法開啟，則設定流的failbit標誌。

(3) 複製建構函式 (已刪除)

已刪除 (無複製建構函式)。

(4) move constructor

獲取 x 的內容。
First, the function move-constructs both its base basic_istream class from x and a basic_filebuf object from x's internal basic_filebuf object, and then associates them by calling member set_rdbuf.
x 處於未指定但有效的狀態。

引數

filename

A string representing the name of the file to open.
有關其格式和有效性的具體說明取決於庫實現和執行環境。

mode

描述檔案請求的 i/o 模式的標誌。
這是一個位掩碼成員型別 openmode 的物件，由以下成員常量的組合構成：

成員常量	代表	access
in *	輸入	檔案以讀模式開啟：內部流緩衝區支援輸入操作。
下可用的型別	輸出	檔案以寫模式開啟：內部流緩衝區支援輸出操作。
binary	binary	操作以二進位制模式執行，而非文字模式。
ate	在末尾	輸出位置從檔案末尾開始。
app	append (追加)	所有輸出操作都在檔案末尾進行，追加到其現有內容。
trunc	truncate (截斷)	檔案開啟前存在的任何內容都將被丟棄。

這些標誌可以透過按位或運算子（|）組合。
* in is always set for basic_ifstream objects (even if explicitly not set in argument mode).
Note that even though basic_ifstream is an input stream, its internal basic_filebuf object may be set to also support output operations.

如果模式設定了 app，則開啟操作失敗。如果設定了 trunc 但未設定 out，操作也會失敗。

如果模式同時設定了 trunc 和 app，則開啟操作失敗。如果設定了 trunc 但未設定 out，操作也會失敗。

x

A basic_ifstream object of the same type (with the same class template parameters charT and traits), whose value is moved.

示例

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// ifstream constructor.
#include <iostream>     // std::cout
#include <fstream>      // std::ifstream

int main () {

  std::ifstream ifs ("test.txt", std::ifstream::in);

  char c = ifs.get();

  while (ifs.good()) {
    std::cout << c;
    c = ifs.get();
  }

  ifs.close();

  return 0;
}

資料競爭

異常安全

另見

basic_ifstream::open

開啟檔案 (公開成員函式)