Question

I want to open a new log file each a program runs, so I create a filename with the current time.

FILE * fplog;

void OpenLog()
{
    boost::posix_time::ptime now = boost::posix_time::second_clock::local_time();
    char buf[256];
    sprintf(buf,"ecrew%d%02d%02d_%02d%02d%02d.log",
        now.date().year(),now.date().month(),now.date().day(),
        now.time_of_day().hours(),now.time_of_day().minutes(),now.time_of_day().seconds()); 
    fplog = fopen(buf,"w");

}

This works perfectly in a debug build, producing files with names such as

ecrew20110309_141506.log

However the same code fails strangely in a release build

ecrew198619589827196617_141338.log

BTW, this also fails in the same way:

boost::posix_time::ptime now = boost::posix_time::second_clock::local_time();
char buf[256];

boost::gregorian::date day (boost::gregorian::day_clock::local_day());

sprintf(buf,"ecrew%d%02d%02d_%02d%02d%02d.log",
    day.year(),day.month(),day.day(),
now.time_of_day().hours(),now.time_of_day().minutes(),now.time_of_day().seconds()); 

fplog = fopen(buf,"w");

This works:

boost::posix_time::ptime now = boost::posix_time::second_clock::local_time();
char buf[256];
sprintf(buf,"ecrew%s_%02d%02d%02d.log",
    to_iso_string( boost::gregorian::day_clock::local_day() ).c_str(),
    now.time_of_day().hours(),now.time_of_day().minutes(),now.time_of_day().seconds()); 
fplog = fopen(buf,"w");

I’d still be curious why the previous two version fail in release build, but work in debug.

Answer 1

Okay I’m a bit late but as I stumbled on to your question when looking for the answer myself ( day_clock::local_day() gives weird results when compiled as Release, here on Win XP + Boost 1.46 ) ,
I thought I should come back with what worked for me.

The data seems to be stocked (I just use year, month and day) in a 16 bit manner but when you read them you get a 32 bit integer and whatever bug there is, it writes garbage into the top bits or it doesn’t clean ’em out before writing to the lower bytes.

So my workaround is just to zero out the topmost 16 bits:

date todaysdate(day_clock::local_day());
int year = todaysdate.year() & 0xFFFF;

instead of say:

date todaysdate(day_clock::local_day());
int year = todaysdate.year();

and it works well for me anyway.

Valmond