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  • fostream创建文件

    Flag     Function
    ios::in  Opens an input file. Use this as an open mode for an ofstreamto prevent truncating an existing file.
    ios::out  Opens an output file. When used for an ofstreamwithout ios::app, ios::ateor ios::in, ios::truncis implied.
    ios::app  Opens an output file for appending.
    ios::ate  Opens an existing file (either input or output) and seeks the end.
    ios::nocreate  Opens a file only if it already exists. (Otherwise it fails.)
    ios::noreplace  Opens a file only if it does not exist. (Otherwise it fails.)
    ios::trunc  Opens a file and deletes the old file, if it already exists.
    ios::binary  Opens a file in binary mode. Default is text mode.

       1:  #include "require.h"
       2:  #include <iostream>
       3:  #include <fstream>
       4:  using namespace std;
       5:   
       6:  int main() {
       7:      ifstream in("Iofile.cpp");
       8:      assure(in, "Iofile.cpp");
       9:      ofstream out("Iofile.out");
      10:      assure(out, "Iofile.out");
      11:      out << in.rdbuf(); // Copy file
      12:      in.close();
      13:      out.close();
      14:      // Open for reading and writing:
      15:      ifstream in2("Iofile.out", ios::in | ios::out);
      16:      assure(in2, "Iofile.out");
      17:      ostream out2(in2.rdbuf());//输出流
      18:      cout << in2.rdbuf();  // Print whole file
      19:      out2 << "Where does this end up?";//这句话跟在结尾
      20:      out2.seekp(0, ios::beg);//设置了out2的输出起始位置
      21:      out2 << "And what about this?";//这句话在开始写入,覆盖了原始数据
      22:      in2.seekg(0, ios::beg);//从起始位置开始读入数据
      23:      cout << in2.rdbuf();//写到标准输出
      24:  } ///:~

    这段程序首先打开一个已有的文件,并将所有的数据copy到一个输出文件中去。

    然后打开一个文件IOfile.out并打开一个输出流ostream out2设置为in2.rdbuf(),然后首次输出了in2的内容。这里out2可以对in2.rdbuf()中的数据进行写入。

    然后分别在输出流中的内容中前边和后边分别插入了一段字符。输出了in2.rdbuf();

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  • 原文地址:https://www.cnblogs.com/pang1567/p/3990735.html
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