在 C++ 中的文件(日志文件)中添加新行 [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，我有日志文件.现在每次运行程序时，我都希望以前写入的文件不应被删除，而应附加当前数据(日志文件中的内容)

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)

只是为了说明清楚，例如:我有一个日志文件 logging_20120409.log，它每天都保存时间戳.假设我运行我的项目，它会将当前时间戳写入其中.现在，如果我重新运行它，以前的时间戳将被替换.我不想要这个功能.我想要上一个时间戳和当前时间戳.

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

您想以追加"模式打开文件，因此它不会删除文件的先前内容.您可以通过在打开文件时指定 ios_base::app 来实现:

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，每次运行时，它都会在文件中多添加一行:

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，当你第一次运行它时，你会得到

So, the first time you run it, you get

line

第二次:

line
line

等等.

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