c++ PRINT macro linux - add date and time

in my c++ linux application I have this macro:

#define PRINT(format,arg...) printf(format,##arg)

I want to add a date and time to the beggining of the string that come to PRINT. (it is a log, so I want it at runtime, with variables) how to change this macro in order to d开发者_如何学JAVAo it?

thanks

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Do you want compile time or runtime added to the string? If the former:

#define PRINT(format,arg...) printf(__DATE__ ":" __TIME__ "  " format,##arg)

will work most of the time.

Note that this will only work if invocations of PRINT only use a string literal for the format string. (ie, PRINT( "foo" ) will work, but PRINT( x ) where x is a variable will not).

If you want a runtime date and time, just append "%s" to the format and then add a call to a function that returns what you want before the arguments.

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If you want local runtime date and can use boost.date_time

#define DATE_TODAY to_simple_string(day_clock::local_day())
#define PRINT(format,arg...) printf( (DATE_TODAY + ": " + format).c_str(), ##arg)

You can also use day_clock::universal_day() if you want UTC time.

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Assuming that you want the compile time date and that you compiler has a __DATE__ macro that returns the date

#define PRINT(format,arg...) printf(__DATE__ ": " format,##arg)

If you want runtime date, then you can do something like that:

std::string format_current_time()
{
   // format the time as you like and return it as an std::string
}

#define PRINT(format,arg...) printf("%s: " format, format_current_time.c_str(), ##arg)

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If you need the current datetime, you have to implement a regular function to do what you ask, since it's impossible for a C macro to return the data you are looking for.

Remember that a C macro is replaced by the C preprocessor at compile time.