追加在C在一个文件（日志文件）的新行++ [英] Appending a new line in a file(log file) in c++

问题描述

我有一个日志记录功能，并在此我有日志文件。现在，每当我运行程序时我想要的previously书面文件不应该被删除，并应与当前数据被追加（曾经是那里的日志文件）

I have a logging functionality and in this I have got log files. Now every time I run the program I want that previously written file should not get deleted and should be appended with the current data (what ever is there in the log file)

只是要清楚，例如：我有这使每天的基础上的时间戳的日志文件logging_20120409.log。假设我跑我的项目写入它的当前时间戳。现在，如果我重新运行它的previous时间戳被它取代。我不想要这个功能。我想previous时间戳与当前时间戳一起。

Just to make it clear for example: I have a log file logging_20120409.log which keeps the timestamp on a daily basis. Suppose I run my project it writes to it the current timestamp. Now if I rerun it the previous timestamp gets replaced with it. I do not want this functionality. I want the previous time stamp along with the current time stamp.

请帮忙

推荐答案

您想打开追加模式下的文件，所以它不会删除该文件的previous内容。你通过指定的ios_bas​​e ::应用当你打开文件：

You want to open the file in "append" mode, so it doesn't delete the previous contents of the file. You do that by specifying ios_base::app when you open the file:

std::ofstream log("logfile.txt", std::ios_base::app | std::ios_base::out);

例如，每次运行这个时候，它会多一个行添加到文件：

For example, each time you run this, it will add one more line to the file:

#include <ios>
#include <fstream>

int main(){
    std::ofstream log("logfile.txt", std::ios_base::app | std::ios_base::out);

    log << "line\n";
    return 0;
}

所以，你运行它的第一次，你会得到

So, the first time you run it, you get

line

第二次：

line
line

等。

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