C++：写入现有文件？
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C++: Write to an existing file?
提问by olidev
In C++, I need to write to an existing file and keep the previous content there.
在 C++ 中，我需要写入现有文件并将以前的内容保留在那里。
This is what I have done:
这就是我所做的：
std::ofstream logging;
logging.open(FILENAME);
logging << "HELLO\n";
logging.close();
but then my previous text is overwritten (gone). What did I do wrong?
但后来我以前的文字被覆盖（消失）。我做错了什么？
Thanks in advance.
提前致谢。
回答by Alexey Malistov
logging.open(FILENAME, std::ios_base::app);
回答by Drew Frezell
You have to open the file in append mode:
您必须以追加模式打开文件：
logging.open(FILENAME, std::ios::app);
回答by luke
By default the "opening mode" for a file is overwrite. Try opening the file in append mode
默认情况下，文件的“打开模式”会被覆盖。尝试以追加模式打开文件
The second parameter of openis an enum bitflag. The two options you should check out are:
的第二个参数open是一个枚举位标志。您应该检查的两个选项是：
- app - seek to the file end before each write
ate - seek to the file end after open
logging.open(FILENAME, std::ios::app|std::ate);
- app - 在每次写入之前寻找文件结尾
ate - 打开后寻找文件末尾
logging.open(文件名，std::ios::app|std::ate);
回答by Sanja Melnichuk
do you try ? something like that
你试试？类似的东西
myFile.open( "file.txt", ios::out | ios::app );
