Don't use 0 as null pointer constant, part 1

Use NULL instead of 0, for clarity.  Except in pointer comparisons;
leave that to the next two commits.

doc/coding

@@ -288,6 +288,10 @@ Do not use increment operators to set a variable to logical true!  It
 obfuscates the purpose, and narrow variables could even overflow.
 Just assign 1.  A lot of cleanup remains to be done there.
 
+Null pointer constant
+
+Please use NULL for clarity, not just 0.
+
 Type casts
 
 Casting pointers to and from `void *' clutters the code and serves no

src/client/termlib.c

@@ -42,8 +42,8 @@
 #include <unistd.h>
 #include "misc.h"
 
-static char *smso = 0;
+static char *smso;
-static char *rmso = 0;
+static char *rmso;
 
 void
 getsose(void)

src/lib/commands/assa.c

@@ -74,7 +74,7 @@ assa(void)
 	return RET_SYN;
     if (!sarg_xy(p, &def->x, &def->y))
 	return RET_SYN;
-    if (att_abort(A_ASSAULT, 0, def))
+    if (att_abort(A_ASSAULT, NULL, def))
 	return RET_FAIL;
 
     /*
@@ -110,7 +110,7 @@ assa(void)
     if (att_abort(A_ASSAULT, off, def)) {
 	pr("Assault aborted\n");
 	att_empty_attack(A_ASSAULT, 0, def);
-	return att_free_lists(&olist, 0);
+	return att_free_lists(&olist, NULL);
     }
 
     /* If we're assaulting our own sector, end here */
@@ -127,7 +127,7 @@ assa(void)
     if (att_abort(A_ASSAULT, off, def)) {
 	pr("Assault aborted\n");
 	att_empty_attack(A_ASSAULT, 0, def);
-	return att_free_lists(&olist, 0);
+	return att_free_lists(&olist, NULL);
     }
 
     /*

src/lib/commands/atta.c

@@ -73,7 +73,7 @@ atta(void)
 	return RET_SYN;
     if (!sarg_xy(p, &def->x, &def->y))
 	return RET_SYN;
-    if (att_abort(A_ATTACK, 0, def))
+    if (att_abort(A_ATTACK, NULL, def))
 	return RET_FAIL;
 
     /* Show what we're attacking, and check treaties */
@@ -84,7 +84,7 @@ atta(void)
     /* Ask about offensive support */
 
     att_ask_support(2, &fort_sup, &ship_sup, &land_sup, &plane_sup);
-    if (att_abort(A_ATTACK, 0, def)) {
+    if (att_abort(A_ATTACK, NULL, def)) {
 	att_empty_attack(A_ATTACK, 0, def);
 	return RET_OK;
     }
@@ -110,14 +110,14 @@ atta(void)
     if (att_abort(A_ATTACK, off, def)) {
 	pr("Attack aborted\n");
 	att_empty_attack(A_ATTACK, 0, def);
-	return att_free_lists(&olist, 0);
+	return att_free_lists(&olist, NULL);
     }
 
     ototal = att_get_offense(A_ATTACK, off, &olist, def);
     if (att_abort(A_ATTACK, off, def)) {
 	pr("Attack aborted\n");
 	att_empty_attack(A_ATTACK, 0, def);
-	return att_free_lists(&olist, 0);
+	return att_free_lists(&olist, NULL);
     }
 
     /*

src/lib/commands/boar.c

@@ -136,14 +136,14 @@ boar(void)
     if (att_abort(A_BOARD, off, def)) {
 	pr("Board aborted\n");
 	att_empty_attack(A_BOARD, 0, def);
-	return att_free_lists(&olist, 0);
+	return att_free_lists(&olist, NULL);
     }
 
     ototal = att_get_offense(A_BOARD, off, &olist, def);
     if (att_abort(A_BOARD, off, def)) {
 	pr("Board aborted\n");
 	att_empty_attack(A_BOARD, 0, def);
-	return att_free_lists(&olist, 0);
+	return att_free_lists(&olist, NULL);
     }
 
     /*

src/lib/commands/bomb.c

@@ -122,7 +122,7 @@ bomb(void)
     (void)pathtoxy(flightpath, &tx, &ty, fcost);
     pr("target sector is %s\n", xyas(tx, ty, player->cnum));
     getsect(tx, ty, &target);
-    ip = 0;
+    ip = NULL;
     ap_to_target = strlen(flightpath);
     if (flightpath[ap_to_target - 1] == 'h')
 	ap_to_target--;

src/lib/commands/buil.c

@@ -540,7 +540,7 @@ build_bridge(struct sctstr *sp, short *vec)
 
     if ((val = chkdir(*p, DIR_FIRST, DIR_LAST)) < 0) {
 	pr("'%c' is not a valid direction...\n", *p);
-	direrr(0, 0, 0);
+	direrr(NULL, NULL, NULL);
 	return 0;
     }
     newx = sp->sct_x + diroff[val][0];
@@ -816,7 +816,7 @@ build_tower(struct sctstr *sp, short *vec)
 
     if ((val = chkdir(*p, DIR_FIRST, DIR_LAST)) < 0) {
 	pr("'%c' is not a valid direction...\n", *p);
-	direrr(0, 0, 0);
+	direrr(NULL, NULL, NULL);
 	return 0;
     }
     newx = sp->sct_x + diroff[val][0];

src/lib/commands/coas.c

@@ -70,7 +70,7 @@ coas(void)
     if (!snxtsct(&nstr, player->argp[1]))
 	return RET_SYN;
     for (i = 0; i < TSIZE; i++)
-	list[i] = 0;
+	list[i] = NULL;
     cp = malloc(sizeof(*cp));
     snxtitem_all(&ni, EF_SHIP);
     while (nxtitem(&ni, &cp->c_shp)) {
@@ -139,18 +139,18 @@ static int
 showship(struct coast **cpp, int x, int y)
 {
     struct coast *cp;
-    struct coast *todelete = 0;
+    struct coast *todelete = NULL;
     struct coast **prev;
     int nship = 0;
 
-    prev = 0;
+    prev = NULL;
     cp = *cpp;
     prev = cpp;
     do {
 	/* we delete it, we free it. */
 	if (todelete) {
 	    free(todelete);
-	    todelete = 0;
+	    todelete = NULL;
 	}
 	if (cp->c_shp.shp_x != x || cp->c_shp.shp_y != y) {
 	    prev = &(*prev)->c_next;

src/lib/commands/expl.c

@@ -119,7 +119,7 @@ explore(void)
 	pr("Only exploring with %d.\n", amount);
     }
 
-    if (!want_to_abandon(&sect, vtype, amount, 0)) {
+    if (!want_to_abandon(&sect, vtype, amount, NULL)) {
 	pr("Explore cancelled.\n");
 	return RET_FAIL;
     }

src/lib/commands/flash.c

@@ -124,7 +124,7 @@ sendmessage(struct natstr *us, struct natstr *to, char *message, int verbose)
 
     time(&now);
     tm = localtime(&now);
-    for (other = player_next(0); other != 0; other = player_next(other)) {
+    for (other = player_next(NULL); other; other = player_next(other)) {
 	if (other->state != PS_PLAYING)
 	    continue;
 	if (to && other->cnum != to->nat_cnum)

src/lib/commands/lboard.c

@@ -107,14 +107,14 @@ lboa(void)
     if (att_abort(A_LBOARD, off, def)) {
 	pr("Land unit boarding aborted\n");
 	att_empty_attack(A_LBOARD, 0, def);
-	return att_free_lists(&olist, 0);
+	return att_free_lists(&olist, NULL);
     }
 
     ototal = att_get_offense(A_LBOARD, off, &olist, def);
     if (att_abort(A_LBOARD, off, def)) {
 	pr("Land unit boarding aborted\n");
 	att_empty_attack(A_LBOARD, 0, def);
-	return att_free_lists(&olist, 0);
+	return att_free_lists(&olist, NULL);
     }
 
     /*

src/lib/commands/load.c

@@ -706,7 +706,7 @@ load_comm_ship(struct sctstr *sectp, struct shpstr *sp,
 			   load_unload, atoi(p));
     if (!load_comm_ok(sectp, sp->shp_own, item, move_amt))
 	return RET_OK;
-    if (!want_to_abandon(sectp, item, move_amt, 0))
+    if (!want_to_abandon(sectp, item, move_amt, NULL))
 	return RET_FAIL;
     if (!still_ok_ship(sectp, sp))
 	return RET_SYN;

src/lib/commands/move.c

@@ -140,7 +140,7 @@ move(void)
 	}
     }
 
-    if (!istest && !want_to_abandon(&sect, vtype, amount, 0)) {
+    if (!istest && !want_to_abandon(&sect, vtype, amount, NULL)) {
 	pr("Move cancelled.\n");
 	return RET_FAIL;
     }

src/lib/commands/para.c

@@ -128,7 +128,7 @@ paradrop(struct emp_qelem *list, coord x, coord y)
     att_combat_init(def, EF_SECTOR);
     def->x = x;
     def->y = y;
-    if (att_abort(A_PARA, 0, def))
+    if (att_abort(A_PARA, NULL, def))
 	return RET_FAIL;
 
     /* Show what we're air-assaulting, and check treaties */

src/lib/commands/play.c

@@ -47,7 +47,7 @@ play(void)
     int saw = 0;
 
     play_header();
-    for (joe = player_prev(0); joe; joe = player_prev(joe)) {
+    for (joe = player_prev(NULL); joe; joe = player_prev(joe)) {
 	saw += play_list(joe);
     }
     if (player->god || opt_BLITZ)

src/lib/commands/reco.c

@@ -97,12 +97,12 @@ reco(void)
     /*
      * now arm and equip the bombers, transports, whatever.
      */
-    pln_arm(&bomb_list, ap_to_target, 'r', 0, P_S | P_I);
+    pln_arm(&bomb_list, ap_to_target, 'r', NULL, P_S | P_I);
     if (QEMPTY(&bomb_list)) {
 	pr("No planes could be equipped for the mission.\n");
 	return RET_FAIL;
     }
-    pln_arm(&esc_list, ap_to_target, 'r', 0, P_F | P_ESC);
+    pln_arm(&esc_list, ap_to_target, 'r', NULL, P_F | P_ESC);
     ac_encounter(&bomb_list, &esc_list, ax, ay, flightpath,
 		 *player->argp[0] == 's' ? PM_R | PM_S : PM_R);
     if (QEMPTY(&bomb_list)) {

src/lib/commands/skyw.c

@@ -68,7 +68,7 @@ skyw(void)
     if (!snxtsct(&nstr, player->argp[1]))
 	return RET_SYN;
     for (i = 0; i < TSIZE; i++)
-	list[i] = 0;
+	list[i] = NULL;
     skyp = malloc(sizeof(*skyp));
     snxtitem_all(&ni, EF_PLANE);
     while (nxtitem(&ni, &skyp->s_sat)) {
@@ -131,20 +131,20 @@ static int
 showsat(struct sky **skypp, int x, int y)
 {
     struct sky *skyp;
-    struct sky *todelete = 0;
+    struct sky *todelete = NULL;
     struct sky **prev;
     struct plchrstr *pcp;
     char *name;
     int nsat = 0;
 
-    prev = 0;
+    prev = NULL;
     skyp = *skypp;
     prev = skypp;
     do {
 	/* we delete it, we free it. */
 	if (todelete) {
 	    free(todelete);
-	    todelete = 0;
+	    todelete = NULL;
 	}
 	if (skyp->s_sat.pln_x != x || skyp->s_sat.pln_y != y) {
 	    prev = &(*prev)->s_next;

src/lib/commands/stre.c

@@ -82,7 +82,7 @@ stre(void)
 	    pr("%7s", "");
 
 	if (def->sct_type != SCT_MOUNT)
-	    r_total = att_reacting_units(def, 0, 0, &dummy, 9999999);
+	    r_total = att_reacting_units(def, NULL, 0, &dummy, 9999999);
 	else
 	    r_total = 0.0;
 	def->own = 0;

src/lib/common/emp_config.c

@@ -154,7 +154,7 @@ keylookup(char *command, struct keymatch *tbl)
     struct keymatch *kp;
 
     if (command == 0 || *command == 0)
-	return 0;
+	return NULL;
     for (kp = tbl; kp->km_key != 0; kp++) {
 	if (strcmp(kp->km_key, command) == 0)
 	    return kp;

src/lib/common/nat.c

@@ -50,7 +50,7 @@ cname(natid n)
     struct natstr *np;
 
     if ((np = getnatp(n)) == 0)
-	return 0;
+	return NULL;
     return np->nat_cnam;
 }
 

src/lib/common/path.c

@@ -185,7 +185,7 @@ bp_neighbors(struct as_coord c, struct as_coord *cp, void *pp)
     int n = 0, q;
     struct sctstr *sp, *from, **ssp;
     /* Six pointers, just in case our cache isn't there */
-    struct sctstr *tsp[] = { 0, 0, 0, 0, 0, 0 };
+    struct sctstr *tsp[] = { NULL, NULL, NULL, NULL, NULL, NULL };
     int sx, sy, offset;
 
     x = c.x;

src/lib/empthread/io.c

@@ -82,8 +82,8 @@ io_open(int fd, int flags, int bufsize, struct timeval timeout)
     if (!iop)
 	return NULL;
     iop->fd = fd;
-    iop->input = 0;
+    iop->input = NULL;
-    iop->output = 0;
+    iop->output = NULL;
     iop->flags = 0;
     iop->input_timeout = timeout;
     iop->bufsize = bufsize;

src/lib/empthread/lwp.c

@@ -65,7 +65,7 @@ empth_create(void (*entry)(void *), int size, int flags,
 {
     if (!flags)
 	flags = empth_flags;
-    return lwpCreate(1, entry, size, flags, name, 0, 0, ud);
+    return lwpCreate(1, entry, size, flags, name, 0, NULL, ud);
 }
 
 empth_t *

src/lib/gen/ioqueue.c

@@ -62,7 +62,7 @@ ioq_create(int size)
     ioq->list.nbytes = 0;
     ioq->list.offset = 0;
     ioq->list.size = 0;
-    ioq->list.data = 0;
+    ioq->list.data = NULL;
     ioq->bufsize = size;
     ioq->cc = 0;
     return ioq;

src/lib/lwp/lwp.c

@@ -98,7 +98,7 @@ lwpReschedule(void)
 	    } else {
 		lwpDestroy(nextp);
 	    }
-	    nextp = 0;
+	    nextp = NULL;
 	}
 	if (nextp)
 	    break;
@@ -315,18 +315,19 @@ lwpInitSystem(int pri, void **ctxptr, int flags, sigset_t *waitset)
 	pri = LWP_MAX_PRIO - 1;
     if (LwpMaxpri < pri)
 	LwpMaxpri = pri;
-    LwpCurrent->next = 0;
+    LwpCurrent->next = NULL;
     LwpCurrent->sbtm = stack;	/* dummy stack for "main" */
     LwpCurrent->pri = pri;
     LwpCurrent->dead = 0;
     LwpCurrent->flags = flags & ~LWP_STACKCHECK;
     LwpCurrent->name = "Main";
     for (i = LWP_MAX_PRIO, q = LwpSchedQ; i--; q++)
-	q->head = q->tail = 0;
+	q->head = q->tail = NULL;
-    LwpDeadQ.head = LwpDeadQ.tail = 0;
+    LwpDeadQ.head = LwpDeadQ.tail = NULL;
     lwpInitSigWait(waitset);
     /* must be lower in priority than us for this to work right */
-    sel = lwpCreate(0, lwpSelect, 16384, flags, "EventHandler", 0, 0, 0);
+    sel = lwpCreate(0, lwpSelect, 16384, flags, "EventHandler", 0,
+		    NULL, NULL);
     lwpInitSelect(sel);
     return LwpCurrent;
 }

src/lib/lwp/queue.c

@@ -34,6 +34,7 @@
 
 #include <config.h>
 
+#include <stddef.h>
 #include "lwp.h"
 #include "lwpint.h"
 
@@ -43,7 +44,7 @@ lwpGetFirst(struct lwpQueue *q)
     struct lwpProc *head;
 
     if ((head = q->head) && !(q->head = head->next))
-	q->tail = 0;
+	q->tail = NULL;
     return head;
 }
 
@@ -55,5 +56,5 @@ lwpAddTail(struct lwpQueue *q, struct lwpProc *p)
     else
 	q->tail->next = p;
     q->tail = p;
-    p->next = 0;
+    p->next = NULL;
 }

src/lib/lwp/sel.c

@@ -73,8 +73,8 @@ lwpInitSelect(struct lwpProc *proc)
     FD_ZERO(&LwpReadfds);
     FD_ZERO(&LwpWritefds);
     LwpFdwait = calloc(FD_SETSIZE, sizeof(struct lwpProc *));
-    LwpDelayq.head = 0;
+    LwpDelayq.head = NULL;
-    LwpDelayq.tail = 0;
+    LwpDelayq.tail = NULL;
     LwpSelProc = proc;
 }
 
@@ -141,7 +141,7 @@ lwpWakeupFd(struct lwpProc *proc)
     FD_CLR(proc->fd, &LwpReadfds);
     FD_CLR(proc->fd, &LwpWritefds);
     LwpNfds--;
-    LwpFdwait[proc->fd] = 0;
+    LwpFdwait[proc->fd] = NULL;
     proc->fd = -1;
     lwpReady(proc);
 }
@@ -158,7 +158,7 @@ lwpWakeupSleep(void)
 
     if (LwpDelayq.head) {
 	now = time(NULL);
-	save.tail = save.head = 0;
+	save.tail = save.head = NULL;
 	while (NULL != (proc = lwpGetFirst(&LwpDelayq))) {
 	    if (now >= proc->runtime) {
 		lwpStatus(proc, "sleep done");

src/lib/lwp/status.c

@@ -51,8 +51,8 @@ lwpStatus(struct lwpProc *proc, char *format, ...)
     va_start(ap, format);
     if (proc->flags & LWP_PRINT) {
 	if (startTime.tv_sec == 0)
-	    gettimeofday(&startTime, 0);
+	    gettimeofday(&startTime, NULL);
-	gettimeofday(&tv, 0);
+	gettimeofday(&tv, NULL);
 	sec = tv.tv_sec - startTime.tv_sec;
 	msec = (tv.tv_usec - startTime.tv_usec) / 1000;
 	if (msec < 0) {

src/lib/player/accept.c

@@ -107,7 +107,7 @@ player_delete(struct player *lp)
     if (lp->iop) {
 	/* it's a real player */
 	io_close(lp->iop);
-	lp->iop = 0;
+	lp->iop = NULL;
     }
     free(lp);
     /* XXX may need to free bigmap here */
@@ -122,7 +122,7 @@ player_next(struct player *lp)
     else
 	lp = (struct player *)lp->queue.q_forw;
     if (&lp->queue == &Players)
-	return 0;
+	return NULL;
     return lp;
 }
 
@@ -134,7 +134,7 @@ player_prev(struct player *lp)
     else
 	lp = (struct player *)lp->queue.q_back;
     if (&lp->queue == &Players)
-	return 0;
+	return NULL;
     return lp;
 }
 

src/lib/player/empmod.c

@@ -279,5 +279,5 @@ struct cmndstr player_coms[] = {
     {"work <LAND UNITS> <AMOUNT>", 1, work, C_MOD, NORM + MONEY + CAP},
     {"xdump [\"meta\"] <TYPE> [<RECORDS>]", 0, xdump, 0, VIS},
     {"zdone <y|n|c>", 0, zdon, C_MOD, NORM},
-    {0, 0, 0, 0, 0}
+    {NULL, 0, NULL, 0, 0}
 };

src/lib/player/login.c

@@ -69,7 +69,7 @@ static struct cmndstr login_coms[] = {
     {"quit", 0, quit_cmd, 0, 0},
     {"sanc", 0, sanc_cmd, 0, 0},
     {"user name", 0, user_cmd, 0, 0},
-    {0, 0, 0, 0, 0}
+    {NULL, 0, NULL, 0, 0}
 };
 
 /*ARGSUSED*/

src/lib/subs/aircombat.c

@@ -295,7 +295,7 @@ sam_intercept(struct emp_qelem *att_list, struct emp_qelem *def_list,
 		&& pp->pln_radius < mapdist(x, y, pp->pln_opx, pp->pln_opy))
 		continue;
 	    if (CANT_HAPPEN(pp->pln_flags & PLN_LAUNCHED)
-		|| mission_pln_equip(dplp, 0, P_F, 0) < 0) {
+		|| mission_pln_equip(dplp, NULL, P_F, 0) < 0) {
 		emp_remque(dqp);
 		free(dqp);
 		continue;
@@ -369,7 +369,7 @@ ac_intercept(struct emp_qelem *bomb_list, struct emp_qelem *esc_list,
 	    && pp->pln_radius < mapdist(x, y, pp->pln_opx, pp->pln_opy))
 	    continue;
 	if (CANT_HAPPEN(pp->pln_flags & PLN_LAUNCHED)
-	    || mission_pln_equip(plp, 0, P_F, 0) < 0) {
+	    || mission_pln_equip(plp, NULL, P_F, 0) < 0) {
 	    emp_remque(qp);
 	    free(qp);
 	    continue;

src/lib/subs/attsub.c

@@ -912,7 +912,7 @@ ask_off(int combat_mode, struct combat *off, struct combat *def)
 	sprintf(prompt, "Number of mil from %s (max %d) : ",
 		prcom(0, off), mob_support);
     }
-    if ((attacking_mil = onearg(0, prompt)) < 0)
+    if ((attacking_mil = onearg(NULL, prompt)) < 0)
 	abort_attack();
     if (att_abort(combat_mode, off, def))
 	return 0;
@@ -1271,7 +1271,8 @@ get_ototal(int combat_mode, struct combat *off, struct emp_qelem *olist,
     for (qp = olist->q_forw; qp != olist; qp = next) {
 	next = qp->q_forw;
 	llp = (struct ulist *)qp;
-	if (check && !get_land(combat_mode, 0, llp->unit.land.lnd_uid, llp, 0))
+	if (check &&
+	    !get_land(combat_mode, NULL, llp->unit.land.lnd_uid, llp, 0))
 	    continue;
 	if (combat_mode == A_ATTACK) {
 	    w = -1;
@@ -1448,7 +1449,7 @@ put_land(struct emp_qelem *list)
 	    emp_remque((struct emp_qelem *)llp);
 	    free(llp);
 	} else
-	    get_land(A_ATTACK, 0, llp->unit.land.lnd_uid, llp, 0);
+	    get_land(A_ATTACK, NULL, llp->unit.land.lnd_uid, llp, 0);
     }
 }
 
@@ -2181,7 +2182,7 @@ take_def(int combat_mode, struct emp_qelem *list, struct combat *off,
 {
     int n;
     int occuppied = 0;
-    struct ulist *llp, *delete_me = 0;
+    struct ulist *llp, *delete_me = NULL;
     char buf[1024];
     struct sctstr sect;
     struct shpstr ship;

src/lib/subs/getstarg.c

@@ -48,7 +48,7 @@ getstarg(char *input, char *prompt, char *buf)
     *buf = '\0';
     if (input == 0 || *input == 0) {
 	if (getstring(prompt, buf) == 0)
-	    return 0;
+	    return NULL;
     } else {
 	strcpy(buf, input);
     }

src/lib/subs/list.c

@@ -254,7 +254,7 @@ adj_units(coord x, coord y, natid own)
 
     for (i = DIR_FIRST; i <= DIR_LAST; i++) {
 	getsect(x + diroff[i][0], y + diroff[i][1], &sect);
-	if (has_units(sect.sct_x, sect.sct_y, own, 0))
+	if (has_units(sect.sct_x, sect.sct_y, own, NULL))
 	    return 1;
     }
     return 0;

src/lib/subs/lndsub.c

@@ -989,7 +989,7 @@ lnd_mar_one_sector(struct emp_qelem *list, int dir, natid actor,
 		    pr("%s was shot and killed.\n", prland(&llp->unit.land));
 		    llp->unit.land.lnd_effic = 0;
 		    putland(llp->unit.land.lnd_uid, &llp->unit.land);
-		    lnd_delete(llp, 0);
+		    lnd_delete(llp, NULL);
 		}
 	    }
 	}

src/lib/subs/mission.c

@@ -610,12 +610,12 @@ perform_mission(coord x, coord y, natid victim, struct emp_qelem *list,
 	/* Split off the escorts at this base into e */
 	divide(&escorts, &e, air->x, air->y);
 
-	mission_pln_arm(&b, air->x, air->y, 2 * md, 'p', 0, 0);
+	mission_pln_arm(&b, air->x, air->y, 2 * md, 'p', NULL, 0);
 
 	if (QEMPTY(&b))
 	    continue;
 
-	mission_pln_arm(&e, air->x, air->y, 2 * md, 'p', 0, P_F | P_ESC);
+	mission_pln_arm(&e, air->x, air->y, 2 * md, 'p', NULL, P_F | P_ESC);
 
 	pp = BestAirPath(buf, air->x, air->y, x, y);
 	if (CANT_HAPPEN(!pp))

src/lib/subs/mslsub.c

@@ -61,7 +61,7 @@ msl_equip(struct plnstr *pp, char mission)
     memset(&pl, 0, sizeof(struct plist));
     pl.pcp = plchr + pp->pln_type;
     pl.plane = *pp;
-    return mission_pln_equip(&pl, 0, 0, mission);
+    return mission_pln_equip(&pl, NULL, 0, mission);
 }
 
 int
@@ -271,7 +271,7 @@ msl_intercept(coord x, coord y, natid bombown, int hardtarget,
 	if (pp->pln_own != sect.sct_own)
 	    continue;
 	pcp = ip->pcp;
-	if (mission_pln_equip(ip, 0, 0, 'i') < 0) {
+	if (mission_pln_equip(ip, NULL, 0, 'i') < 0) {
 	    emp_remque(qp);
 	    free(qp);
 	    continue;
@@ -290,7 +290,7 @@ msl_intercept(coord x, coord y, natid bombown, int hardtarget,
 	ip = (struct plist *)qp;
 	pp = &ip->plane;
 	pcp = ip->pcp;
-	if (mission_pln_equip(ip, 0, 0, 'i') < 0) {
+	if (mission_pln_equip(ip, NULL, 0, 'i') < 0) {
 	    emp_remque(qp);
 	    free(qp);
 	    continue;
@@ -401,7 +401,7 @@ msl_launch_mindam(struct emp_qelem *list, coord x, coord y, int hardtarget,
 	next = qp->q_back;
 	plp = (struct plist *)qp;
 
-	if (mission_pln_equip(plp, 0, 0, 'p') >= 0) {
+	if (mission_pln_equip(plp, NULL, 0, 'p') >= 0) {
 	    if (msl_hit(&plp->plane,
 			hardtarget, type, news_item, snews_item,
 			whatp, x, y, victim)) {

src/lib/subs/pr.c

@@ -201,7 +201,7 @@ pr_wall(char *format, ...)
     va_start(ap, format);
     (void)vsprintf(buf + n, format, ap);
     va_end(ap);
-    for (p = player_next(0); p; p = player_next(p)) {
+    for (p = player_next(NULL); p; p = player_next(p)) {
 	if (p->state != PS_PLAYING)
 	    continue;
 	pr_player(p, C_FLASH, buf);

src/lib/subs/rej.c

@@ -52,7 +52,7 @@ setrel(natid us, natid them, int rel)
     char *whichway;
     int n_up = 0;
     int n_down = 0;
-    char *addendum = 0;
+    char *addendum = NULL;
     int theirrel;
 
     if (rel < AT_WAR)

src/lib/subs/shpsub.c

@@ -423,7 +423,7 @@ most_valuable_ship(struct emp_qelem *list)
     struct emp_qelem *qp;
     struct emp_qelem *next;
     struct ulist *mlp;
-    struct ulist *mvs = 0;
+    struct ulist *mvs = NULL;
 
     for (qp = list->q_back; qp != list; qp = next) {
 	next = qp->q_back;

src/lib/subs/unitsub.c

@@ -147,14 +147,14 @@ unit_path(int together, struct empobj *unit, char *buf)
 	return NULL;
 
     if (!sarg_xy(buf, &destx, &desty))
-	return 0;
+	return NULL;
     if (!together) {
 	pr("Cannot go to a destination sector if not all starting in the same sector\n");
-	return 0;
+	return NULL;
     }
     if (!getsect(destx, desty, &d_sect)) {
 	pr("%d,%d is not a sector\n", destx, desty);
-	return 0;
+	return NULL;
     }
     if (unit->ef_type == EF_SHIP) {
 	cp = BestShipPath(buf, unit->x, unit->y,
@@ -162,7 +162,7 @@ unit_path(int together, struct empobj *unit, char *buf)
 	if (!cp || unit->mobil <= 0) {
 	    pr("Can't get to '%s' right now.\n",
 		xyas(d_sect.sct_x, d_sect.sct_y, player->cnum));
-	    return 0;
+	    return NULL;
 	}
     } else {
 	getsect(unit->x, unit->y, &sect);
@@ -173,7 +173,7 @@ unit_path(int together, struct empobj *unit, char *buf)
 	       mtype == MOB_RAIL ? "railway" : "path",
 	       xyas(unit->x, unit->y, player->cnum),
 	       xyas(d_sect.sct_x, d_sect.sct_y, player->cnum));
-	    return 0;
+	    return NULL;
 	}
 	pr("Using path '%s'\n", cp);
     }

src/lib/subs/whatitem.c

@@ -49,7 +49,7 @@ whatitem(char *input, char *prompt)
 
     p = getstarg(input, prompt, buf);
     if (p == 0 || *p == 0)
-	return 0;
+	return NULL;
     ip = item_by_name(p);
     if (!ip)
 	pr("Unrecognized item \"%c\"\n", *p);
@@ -69,5 +69,5 @@ item_by_name(char *str)
 	if (*str == ip->i_mnem)
 	    return ip;
     }
-    return 0;
+    return NULL;
 }

src/lib/update/nxtitemp.c

@@ -47,16 +47,16 @@ nxtitemp(struct nstr_item *np)
     int selected;
 
     if (np->sel == NS_UNDEF)
-	return 0;
+	return NULL;
     do {
 	if (np->sel == NS_LIST) {
 	    np->index++;
 	    if (np->index >= np->size)
-		return 0;
+		return NULL;
 	    np->cur = np->list[np->index];
 	} else if (np->sel == NS_CARGO) {
 	    if (np->next < 0)
-		return 0;
+		return NULL;
 	    np->cur = np->next;
 	    np->next = unit_cargo_next(np->type, np->next);
 	} else {
@@ -64,7 +64,7 @@ nxtitemp(struct nstr_item *np)
 	}
 	gp = ef_ptr(np->type, np->cur);
 	if (!gp)
-	    return 0;
+	    return NULL;
 
 	selected = 1;
 	switch (np->sel) {
@@ -74,7 +74,7 @@ nxtitemp(struct nstr_item *np)
 	    break;
 	case NS_DIST:
 	    if (CANT_HAPPEN(!(ef_flags(np->type) & EFF_XY)))
-		return 0;
+		return NULL;
 	    if (!xyinrange(gp->x, gp->y, &np->range)) {
 		selected = 0;
 		break;
@@ -85,25 +85,25 @@ nxtitemp(struct nstr_item *np)
 	    break;
 	case NS_AREA:
 	    if (CANT_HAPPEN(!(ef_flags(np->type) & EFF_XY)))
-		return 0;
+		return NULL;
 	    if (!xyinrange(gp->x, gp->y, &np->range))
 		selected = 0;
 	    break;
 	case NS_XY:
 	    if (CANT_HAPPEN(!(ef_flags(np->type) & EFF_XY)))
-		return 0;
+		return NULL;
 	    if (xnorm(gp->x) != np->cx || ynorm(gp->y) != np->cy)
 		selected = 0;
 	    break;
 	case NS_GROUP:
 	    if (CANT_HAPPEN(!(ef_flags(np->type) & EFF_GROUP)))
-		return 0;
+		return NULL;
 	    if (np->group != gp->group)
 		selected = 0;
 	    break;
 	default:
 	    CANT_REACH();
-	    return 0;
+	    return NULL;
 	}
 	if (selected && np->ncond) {
 	    /* nstr_exec is expensive, so we do it last */

src/lib/update/plague.c

@@ -99,7 +99,7 @@ do_plague(struct sctstr *sp, struct natstr *np, int etu)
 	}
     }
     if (sp->sct_item[I_CIVIL] == 0 && sp->sct_item[I_MILIT] == 0
-	&& !has_units(sp->sct_x, sp->sct_y, sp->sct_own, 0)) {
+	&& !has_units(sp->sct_x, sp->sct_y, sp->sct_own, NULL)) {
 	makelost(EF_SECTOR, sp->sct_own, 0, sp->sct_x, sp->sct_y);
 	sp->sct_own = 0;
 	sp->sct_oldown = 0;

src/lib/update/populace.c

@@ -52,7 +52,7 @@ populace(struct natstr *np, struct sctstr *sp, int etu)
 	sp->sct_oldown = sp->sct_own;
     }
     if (!civ && !mil && !sp->sct_item[I_UW]
-	&& !has_units(sp->sct_x, sp->sct_y, sp->sct_own, 0)) {
+	&& !has_units(sp->sct_x, sp->sct_y, sp->sct_own, NULL)) {
 	makelost(EF_SECTOR, sp->sct_own, 0, sp->sct_x, sp->sct_y);
 	sp->sct_own = 0;
 	sp->sct_oldown = 0;

src/lib/update/revolt.c

@@ -352,7 +352,7 @@ guerrilla(struct sctstr *sp)
     }
   domove:
     if (move && che > 0) {
-	struct sctstr *nicest_sp = 0;
+	struct sctstr *nicest_sp = NULL;
 	if (convert)
 	    min_mil = 999;
 	else

src/lib/update/sail.c

@@ -299,7 +299,7 @@ void
 sail_ship(natid cn)
 {
     struct shpstr *sp;
-    struct fltheadstr *head = 0;
+    struct fltheadstr *head = NULL;
     struct fltheadstr *fltp;
     int n;
 

src/lib/update/sect.c

@@ -297,7 +297,7 @@ produce_sect(int natnum, int etu, struct bp *bp, long p_sect[][2])
 	 * they all starved or were plagued off.
 	 */
 	if (vec[I_CIVIL] == 0 && vec[I_MILIT] == 0 &&
-	    !has_units(sp->sct_x, sp->sct_y, sp->sct_own, 0)) {
+	    !has_units(sp->sct_x, sp->sct_y, sp->sct_own, NULL)) {
 	    if (!player->simulation) {
 		makelost(EF_SECTOR, sp->sct_own, 0, sp->sct_x, sp->sct_y);
 		sp->sct_own = 0;

src/server/main.c

@@ -382,7 +382,7 @@ start_server(int flags)
     if (journal_startup() < 0)
 	exit(1);
 
-    empth_create(player_accept, 50 * 1024, flags, "AcceptPlayers", 0);
+    empth_create(player_accept, 50 * 1024, flags, "AcceptPlayers", NULL);
 
     market_init();
     update_init();
@@ -422,7 +422,7 @@ shutdwn(int sig)
     logerror("Shutdown commencing (cleaning up threads.)");
 
     play_wrlock_wanted = 1;
-    for (p = player_next(0); p != 0; p = player_next(p)) {
+    for (p = player_next(NULL); p != 0; p = player_next(p)) {
 	if (p->state != PS_PLAYING)
 	    continue;
 	pr_flash(p, "Server shutting down...\n");

src/server/update.c

@@ -194,7 +194,7 @@ update_run(void)
     struct player *p;
 
     play_wrlock_wanted = 1;
-    for (p = player_next(0); p != 0; p = player_next(p)) {
+    for (p = player_next(NULL); p != 0; p = player_next(p)) {
 	if (p->state != PS_PLAYING)
 	    continue;
 	if (p->command) {