Logging

Placing and output is program-specific

Can perform data-structure traversals

    printf(PDQ_OS_PREFIX "FDDI Port%s = %c (PMD = %s)",
       PDQ_OS_PREFIX_ARGS,
       rsp->status_chars_get.station_type == PDQ_STATION_TYPE_DAS ? "[A]" : "",
       pdq_phy_types[rsp->status_chars_get.phy_type[0]],
       pdq_pmd_types[rsp->status_chars_get.pmd_type[0] / 100]
           [rsp->status_chars_get.pmd_type[0] % 100]);

Stored with the program source code

Careful formatting

    printf("\n");
    printf("%s %s trap:\n", isfatal? "fatal" : "handled",
           user ? "user" : "kernel");
    printf("\n");
    printf("    trap entry = 0x%lx (%s)\n", entry, entryname);
    printf("    a0         = 0x%lx\n", a0);
    printf("    a1         = 0x%lx\n", a1);
    printf("    a2         = 0x%lx\n", a2);
    printf("    pc         = 0x%lx\n", framep->tf_regs[FRAME_PC]);
    printf("    ra         = 0x%lx\n", framep->tf_regs[FRAME_RA]);
    printf("    curproc    = %p\n", curproc);
    if (curproc != NULL)
        printf("        pid = %d, comm = %s\n", curproc->p_pid,
               curproc->p_comm);
    printf("\n");

Adjustable and filterable (syslog, log4j, Apple logging)

import org.apache.log4j.*;
Argo.log.info ("Loading modules from " + file);
Argo.log.warn("Could not instantiate module " + classname);
Argo.log.warn ("Class " + pluginType.getName() + " is not a core Argo pluggable type.");

Useful when a debugger can't be used