Stack traces: Difference between revisions
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Fortran provides nothing of the sort as a language feature. A given compiler may (possibly via an option) record information in the code file that when a fatal error such as divide-by-zero is caught, allows the error message to name the routine in which the error occurred, possibly identifying the source line and perhaps even the sequence of routines that were invoked to get there. Otherwise, a routine has no information whereby it might identify its caller - or for that matter, itself. Some compilers might make available special routines, but, there is no such requirement in the standard.
Otherwise, it is up to the programmer. For instance, on entry to ''every'' routine, <code>CALL SUBIN("''name''")</code> and on exit, ''without fail'', <code>CALL SUBOUT("''name''")</code> which routines maintain a ... stack of names and further can count invocations, though perhaps not for heavily-used routines. Add to this the judicious use of a routine <code>CALL STATE("''activity description''")</code> similarly using a stack (the stack pointer being maintained by SUBIN/SUBOUT) not only provides interesting documentation in the source but also, should there be a disaster, <code>CALL CROAK("''dismayed message''")</code> can be used to end a run, routine CROAK of course displaying the current stack with at each level the declared activity message before a STOP. A similar routine could be invoked to display the current stack state without a STOP as some sort of status report. With this protocol in place, the routine to present trace output can name its caller (and, the caller of that) to provide some context for the bewildering output.
Here for example is a run of such a programme, called Gnash (for New Zealand's national collection of half-hourly electricity data) that accepts certain commands and in particular a command "croak". A log of input and output is maintained, echoing what appears on the screen. Thus, the programme requests the next input after prompting "Gnash:" and that input is the command "croak" followed by some text...
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