Linux - signal: error: invalid use of non-static member function - c++

Question

I originally wrote some tests to test the functionality of signals for my program. The tests proved promising, however moving the small code changes to my class in my source code has given me a few problems.
I have added two functions: setAlarm(), and a callback alarm_handler. setAlarm() does as it says, which is set the alarm. Once time expires, alarm handler is called which runs an execute function.
a.cpp
int Database::alarm_handler(int signum)
{
dbExecSql();
}
void Database::setAlarm()
{
signal(SIGALRM, alarm_handler);
ualarm(500000,0);
}
b.h
class Database
{
public:
int alarm_handler(int signum);
void setAlarm();
dbExecSql();
};
error
error: invalid use of non-static member function
signal(SIGALRM, alarm_handler);
Any help would be appreciated.
EDIT
I have modified alarm_handler to be removed from my class, however am now am receiving:
error: invalid conversion from ‘int (*)(int)’ to ‘__sighandler_t {aka void (*)(int)}’ [-fpermissive]
signal(SIGALRM, alarm_handler);
^

Answer 1

The signal handler function (alarm_handler) can't be member function and should be a standalone function with C linkage.
Remove it from your class:
void alarm_handler(int signum)
{
dbExecSql();
}
Beware that only async-signal-safe functions can be called from signal handlers safely. So you need to ensure dbExecSql() respects that.