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要在 C++ 中进行文件处理,必须在 C++ 源代码文件中包含头文件 <iostream> 和 <fstream>。
在从文件读取信息或者向文件写入信息之前,必须先打开文件。
ofstream 和 fstream 对象都可以用来打开文件进行写操作。
如果只需要打开文件进行读操作,则使用 ifstream 对象。
下面是 open () 函数的标准语法,open () 函数是 fstream、ifstream 和 ofstream 对象的一个成员。
在这里, open () 成员函数的第一个参数指定要打开的文件的名称和位置,第二个参数定义文件被打开的模式。
您可以把以上两种或两种以上的模式结合使用。例如,如果您想要以写入模式打开文件,并希望截断文件,以防文件已存在,那么您可以使用下面的语法:
ofstream outfile; outfile.open("file.dat", ios::out | ios::trunc );
类似地,您如果想要打开一个文件用于读写,可以使用下面的语法:
ifstream afile; afile.open("file.dat", ios::out | ios::in );