Sharing log file among classes

bkelly · 04-09-2019, 12:09 PM

Centos Linux
I have a class that instantiates other classes and want all to write to a single log file. I am unable to find the correct syntax and am not certain that this can easily be done. My searches for topics such as sharing a log file lead to results on piping outputs rather than from within an application.

Below is the basic concept. Can this be done? Maybe some search hints to find what others have discussed?

file a.h contains

Code:

class a{ ...
public
   a( ); 
private:
   std::ofstream m_logs; 
...}; // end of class a

file a.cpp contains

Code:

a::a() {
m_logs.open( "/tmp/a_logs.txt" );
m_logs << "write a stuff"
b = new class_b( std::ofstream & log_file );
...} // end of a constructor

file b.h contains

Code:

class b{ ...
public:
   b( std::ofstream & log_file ); // compile error here
private:
   void x( );
   std::ofstream m_logs;
... } // end class b

The text from the compile error is:

Quote:

error: could not convert '0l' from 'long int' to 'std :: ofstream& {aka std :: basic_ofstream<char>&}'

(side note: added spaces around the some of the colons to prevent emoticons)

I do not understand why it declares that std :: ofstream is a long integer;

file b.cpp contins

Code:

b :: b( std::ofstream & log_file ) {

   m_logs = log_file; // ?
   m_logs << "write b::b stuff" << std::endl;
   x();
...} // end constructor b
b :: x(){ ...
   m_logs << "write b :: x stuff" << std::endl; 
... } // end function b :: x()

tyler2016 · 04-11-2019, 07:12 PM

I don't see where in a.cpp you pass the constructor an ofstream instance? Maybe replace:

Code:

b = new class_b( std::ofstream & log_file );

with:

Code:

b = new class_b( std::ofstream & m_logs );

My first thought was: Is there some reason you can't just log to the system logger and configure it to write everything from your application to a specific file? I am sysad at my day job and would much rather an application log to the syslog than it's own file.

bkelly · 04-17-2019, 11:23 AM

Quote:

Originally Posted by tyler2016

... I am sysad at my day job and would much rather an application log to the syslog than it's own file.

When developing an app and trying to find the defects I have put in, I don't want to write copious quantities of debug info to any system wide log. Thanks for the tip and I am still working on it.

pan64 · 04-17-2019, 12:27 PM

without seeing the real code hard to say anything. If I need to guess that log_file is already declared somewhere as long int.

tyler2016 · 04-18-2019, 07:06 AM

I am pretty rusty on my C++, it has been 3 years or so since I have written any C++. My recollection of new, constructors, etc is a bit foggy. I did a little bit of brushing up and found my comment on how the constructor is called is incorrect.

I think pan64 is probably correct. Try this:

Code:

cd /path/to/src/tree
find . -type f -exec grep -l log_file {} \;

This will show you all files with log_file in it within your source tree.

rtmistler · 04-18-2019, 08:07 AM

You don't "share" across classes.

You define a separate log file class which services the log file and you provide public methods to access it.

rtmistler · 04-18-2019, 08:56 AM

@bkelly,

I see that you've now started a new thread asking for code changes to what you've been trying to accomplish writing to a log file.

Building a TID based file name

While I understand that you have modified your question, it is clearly a continuation of this question where you've learned additional information, and are trying some next steps.

Both of these topics are more suitable for the Programming forum, so I'm closing this one and moving your new question to Programming.

I may have a suggestion for that thread, however it won't be Qt specific because I no longer have a development system with Qt fully installed.

In the future, please consider marking this thread as solved, posting a link to your updated question here as a reference, and also consider which forums may be better for each question subject.