refactor: replace '\0' with NUL

23 files changed, 65 insertions, 62 deletions

diff --git a/src/nvim/base64.c b/src/nvim/base64.c
index a645c64fe3..39e4ec4872 100644
--- a/src/nvim/base64.c
+++ b/src/nvim/base64.c
@@ -4,6 +4,7 @@
 #include <string.h>
 
 #include "auto/config.h"  // IWYU pragma: keep
+#include "nvim/ascii_defs.h"
 #include "nvim/base64.h"
 #include "nvim/memory.h"
 
@@ -125,7 +126,7 @@ char *base64_encode(const char *src, size_t src_len)
     dest[out_i] = '=';
   }
 
-  dest[out_len] = '\0';
+  dest[out_len] = NUL;
 
   return dest;
 }
diff --git a/src/nvim/buffer.c b/src/nvim/buffer.c
index 5d0cd66133..c0fbc36787 100644
--- a/src/nvim/buffer.c
+++ b/src/nvim/buffer.c
@@ -4208,7 +4208,7 @@ int buf_open_scratch(handle_T bufnr, char *bufname)
 
 bool buf_is_empty(buf_T *buf)
 {
-  return buf->b_ml.ml_line_count == 1 && *ml_get_buf(buf, 1) == '\0';
+  return buf->b_ml.ml_line_count == 1 && *ml_get_buf(buf, 1) == NUL;
 }
 
 /// Increment b:changedtick value
diff --git a/src/nvim/charset.c b/src/nvim/charset.c
index c611d4cfd6..430f6b15fe 100644
--- a/src/nvim/charset.c
+++ b/src/nvim/charset.c
@@ -1470,7 +1470,7 @@ start:
         *dst++ = *p++;
       }
     }
-    *dst = '\0';
+    *dst = NUL;
   }
 }
 
@@ -1492,6 +1492,6 @@ char *backslash_halve_save(const char *p)
       *dst++ = *p++;
     }
   }
-  *dst = '\0';
+  *dst = NUL;
   return res;
 }
diff --git a/src/nvim/cmdexpand.c b/src/nvim/cmdexpand.c
index bb85620ce6..0b88e2be11 100644
--- a/src/nvim/cmdexpand.c
+++ b/src/nvim/cmdexpand.c
@@ -3075,7 +3075,7 @@ static void *call_user_expand_func(user_expand_func_T user_expand_func, expand_T
   typval_T args[4];
   const sctx_T save_current_sctx = current_sctx;
 
-  if (xp->xp_arg == NULL || xp->xp_arg[0] == '\0' || xp->xp_line == NULL) {
+  if (xp->xp_arg == NULL || xp->xp_arg[0] == NUL || xp->xp_line == NULL) {
     return NULL;
   }
 
diff --git a/src/nvim/eval.c b/src/nvim/eval.c
index a8778b9489..a4680b62ab 100644
--- a/src/nvim/eval.c
+++ b/src/nvim/eval.c
@@ -8910,7 +8910,7 @@ bool eval_has_provider(const char *feat, bool throw_if_fast)
 
   char name[32];  // Normalized: "python3_compiled" => "python3".
   snprintf(name, sizeof(name), "%s", feat);
-  strchrsub(name, '_', '\0');  // Chop any "_xx" suffix.
+  strchrsub(name, '_', NUL);  // Chop any "_xx" suffix.
 
   char buf[256];
   typval_T tv;
diff --git a/src/nvim/ex_docmd.c b/src/nvim/ex_docmd.c
index 028ee8f6ae..2f54aa511b 100644
--- a/src/nvim/ex_docmd.c
+++ b/src/nvim/ex_docmd.c
@@ -4118,7 +4118,7 @@ static char *getargcmd(char **argp)
 
   if (*arg == '+') {        // +[command]
     arg++;
-    if (ascii_isspace(*arg) || *arg == '\0') {
+    if (ascii_isspace(*arg) || *arg == NUL) {
       command = dollar_command;
     } else {
       command = arg;
diff --git a/src/nvim/file_search.c b/src/nvim/file_search.c
index a8b0dbddee..51bea3111c 100644
--- a/src/nvim/file_search.c
+++ b/src/nvim/file_search.c
@@ -510,7 +510,7 @@ char *vim_findfile_stopdir(char *buf)
   while (*r_ptr != NUL && *r_ptr != ';') {
     if (r_ptr[0] == '\\' && r_ptr[1] == ';') {
       // Overwrite the escape char,
-      // use strlen(r_ptr) to move the trailing '\0'.
+      // use strlen(r_ptr) to move the trailing NUL.
       STRMOVE(r_ptr, r_ptr + 1);
       r_ptr++;
     }
diff --git a/src/nvim/fileio.c b/src/nvim/fileio.c
index 05c9114554..3078f00fbb 100644
--- a/src/nvim/fileio.c
+++ b/src/nvim/fileio.c
@@ -2419,7 +2419,7 @@ char *modname(const char *fname, const char *ext, bool prepend_dot)
 
   // the file name has at most BASENAMELEN characters.
   if (strlen(ptr) > BASENAMELEN) {
-    ptr[BASENAMELEN] = '\0';
+    ptr[BASENAMELEN] = NUL;
   }
 
   char *s = ptr + strlen(ptr);
@@ -3330,7 +3330,7 @@ static void vim_mktempdir(void)
 #endif
       // If our "root" tempdir is invalid or fails, proceed without "<user>/".
       // Else user1 could break user2 by creating "/tmp/nvim.user2/".
-      tmp[strlen(tmp) - strlen(user)] = '\0';
+      tmp[strlen(tmp) - strlen(user)] = NUL;
     }
 
     // Now try to create "/tmp/nvim.<user>/XXXXXX".
diff --git a/src/nvim/help.c b/src/nvim/help.c
index d28f195c00..0da846bb9f 100644
--- a/src/nvim/help.c
+++ b/src/nvim/help.c
@@ -958,8 +958,8 @@ static void helptags_one(char *dir, const char *ext, const char *tagfname, bool
           if (s == p2
               && (p1 == IObuff || p1[-1] == ' ' || p1[-1] == '\t')
               && (vim_strchr(" \t\n\r", (uint8_t)s[1]) != NULL
-                  || s[1] == '\0')) {
-            *p2 = '\0';
+                  || s[1] == NUL)) {
+            *p2 = NUL;
             p1++;
             size_t s_len = (size_t)(p2 - p1) + strlen(fname) + 2;
             s = xmalloc(s_len);
diff --git a/src/nvim/highlight_group.c b/src/nvim/highlight_group.c
index b5e62e7f31..c32e1f9657 100644
--- a/src/nvim/highlight_group.c
+++ b/src/nvim/highlight_group.c
@@ -1174,7 +1174,7 @@ void do_highlight(const char *line, const bool forceit, const bool init)
         break;
       }
       vim_memcpy_up(key, key_start, key_len);
-      key[key_len] = '\0';
+      key[key_len] = NUL;
       linep = skipwhite(linep);
 
       if (strcmp(key, "NONE") == 0) {
@@ -1967,7 +1967,7 @@ int syn_name2id_len(const char *name, size_t len)
   // Avoid using stricmp() too much, it's slow on some systems
   // Avoid alloc()/free(), these are slow too.
   vim_memcpy_up(name_u, name, len);
-  name_u[len] = '\0';
+  name_u[len] = NUL;
 
   // map_get(..., int) returns 0 when no key is present, which is
   // the expected value for missing highlight group.
diff --git a/src/nvim/linematch.c b/src/nvim/linematch.c
index c34b303193..24b2c82381 100644
--- a/src/nvim/linematch.c
+++ b/src/nvim/linematch.c
@@ -5,6 +5,7 @@
 #include <stdint.h>
 #include <string.h>
 
+#include "nvim/ascii_defs.h"
 #include "nvim/linematch.h"
 #include "nvim/macros_defs.h"
 #include "nvim/memory.h"
@@ -61,7 +62,7 @@ static int matching_chars_iwhite(const char *s1, const char *s2)
         d++;
       }
     }
-    strsproc[k][i] = '\0';
+    strsproc[k][i] = NUL;
   }
   int matching = matching_chars(strsproc[0], strsproc[1]);
   xfree(strsproc[0]);
diff --git a/src/nvim/log.c b/src/nvim/log.c
index fbb3e0385a..774f1c956d 100644
--- a/src/nvim/log.c
+++ b/src/nvim/log.c
@@ -46,7 +46,7 @@ static uv_mutex_t mutex;
 
 static bool log_try_create(char *fname)
 {
-  if (fname == NULL || fname[0] == '\0') {
+  if (fname == NULL || fname[0] == NUL) {
     return false;
   }
   FILE *log_file = fopen(fname, "a");
@@ -67,7 +67,7 @@ static void log_path_init(void)
   size_t size = sizeof(log_file_path);
   expand_env("$" ENV_LOGFILE, log_file_path, (int)size - 1);
   if (strequal("$" ENV_LOGFILE, log_file_path)
-      || log_file_path[0] == '\0'
+      || log_file_path[0] == NUL
       || os_isdir(log_file_path)
       || !log_try_create(log_file_path)) {
     // Make $XDG_STATE_HOME if it does not exist.
@@ -88,7 +88,7 @@ static void log_path_init(void)
     }
     // Fall back to stderr
     if (len >= size || !log_try_create(log_file_path)) {
-      log_file_path[0] = '\0';
+      log_file_path[0] = NUL;
       return;
     }
     os_setenv(ENV_LOGFILE, log_file_path, true);
@@ -324,7 +324,7 @@ static bool v_do_log_to_file(FILE *log_file, int log_level, const char *context,
 
   // Get a name for this Nvim instance.
   // TODO(justinmk): expose this as v:name ?
-  if (name[0] == '\0') {
+  if (name[0] == NUL) {
     // Parent servername.
     const char *parent = path_tail(os_getenv(ENV_NVIM));
     // Servername. Empty until starting=false.
@@ -350,7 +350,7 @@ static bool v_do_log_to_file(FILE *log_file, int log_level, const char *context,
                      func_name, line_num);
   if (name[0] == '?') {
     // No v:servername yet. Clear `name` so that the next log can try again.
-    name[0] = '\0';
+    name[0] = NUL;
   }
 
   if (rv < 0) {
diff --git a/src/nvim/mbyte.c b/src/nvim/mbyte.c
index 23fdd5eb16..07c0c846ed 100644
--- a/src/nvim/mbyte.c
+++ b/src/nvim/mbyte.c
@@ -1500,7 +1500,7 @@ int utf8_to_utf16(const char *utf8, int utf8len, wchar_t **utf16)
     return uv_translate_sys_error(GetLastError());
   }
 
-  (*utf16)[bufsize] = L'\0';
+  (*utf16)[bufsize] = LNUL;
   return 0;
 }
 
@@ -1546,7 +1546,7 @@ int utf16_to_utf8(const wchar_t *utf16, int utf16len, char **utf8)
     return uv_translate_sys_error(GetLastError());
   }
 
-  (*utf8)[bufsize] = '\0';
+  (*utf8)[bufsize] = NUL;
   return 0;
 }
 
diff --git a/src/nvim/memory.c b/src/nvim/memory.c
index c4774d68f3..50860c69d0 100644
--- a/src/nvim/memory.c
+++ b/src/nvim/memory.c
@@ -203,7 +203,7 @@ void *xmallocz(size_t size)
   }
 
   void *ret = xmalloc(total_size);
-  ((char *)ret)[size] = '\0';
+  ((char *)ret)[size] = NUL;
 
   return ret;
 }
@@ -233,7 +233,7 @@ void *xmemcpyz(void *dst, const void *src, size_t len)
   FUNC_ATTR_NONNULL_ALL FUNC_ATTR_NONNULL_RET
 {
   memcpy(dst, src, len);
-  ((char *)dst)[len] = '\0';
+  ((char *)dst)[len] = NUL;
   return dst;
 }
 
@@ -241,7 +241,7 @@ void *xmemcpyz(void *dst, const void *src, size_t len)
 size_t xstrnlen(const char *s, size_t n)
   FUNC_ATTR_NONNULL_ALL FUNC_ATTR_PURE
 {
-  const char *end = memchr(s, '\0', n);
+  const char *end = memchr(s, NUL, n);
   if (end == NULL) {
     return n;
   }
@@ -288,7 +288,7 @@ void *xmemscan(const void *addr, char c, size_t size)
 void strchrsub(char *str, char c, char x)
   FUNC_ATTR_NONNULL_ALL
 {
-  assert(c != '\0');
+  assert(c != NUL);
   while ((str = strchr(str, c))) {
     *str++ = x;
   }
@@ -388,7 +388,7 @@ char *xstpcpy(char *restrict dst, const char *restrict src)
 char *xstpncpy(char *restrict dst, const char *restrict src, size_t maxlen)
   FUNC_ATTR_NONNULL_RET FUNC_ATTR_WARN_UNUSED_RESULT FUNC_ATTR_NONNULL_ALL
 {
-  const char *p = memchr(src, '\0', maxlen);
+  const char *p = memchr(src, NUL, maxlen);
   if (p) {
     size_t srclen = (size_t)(p - src);
     memcpy(dst, src, srclen);
@@ -420,7 +420,7 @@ size_t xstrlcpy(char *restrict dst, const char *restrict src, size_t dsize)
   if (dsize) {
     size_t len = MIN(slen, dsize - 1);
     memcpy(dst, src, len);
-    dst[len] = '\0';
+    dst[len] = NUL;
   }
 
   return slen;  // Does not include NUL.
@@ -450,7 +450,7 @@ size_t xstrlcat(char *const dst, const char *const src, const size_t dsize)
 
   if (slen > dsize - dlen - 1) {
     memmove(dst + dlen, src, dsize - dlen - 1);
-    dst[dsize - 1] = '\0';
+    dst[dsize - 1] = NUL;
   } else {
     memmove(dst + dlen, src, slen + 1);
   }
@@ -510,7 +510,7 @@ char *xstrndup(const char *str, size_t len)
   FUNC_ATTR_MALLOC FUNC_ATTR_WARN_UNUSED_RESULT FUNC_ATTR_NONNULL_RET
   FUNC_ATTR_NONNULL_ALL
 {
-  char *p = memchr(str, '\0', len);
+  char *p = memchr(str, NUL, len);
   return xmemdupz(str, p ? (size_t)(p - str) : len);
 }
 
diff --git a/src/nvim/message.c b/src/nvim/message.c
index 9941dcb254..73712489ad 100644
--- a/src/nvim/message.c
+++ b/src/nvim/message.c
@@ -2690,7 +2690,7 @@ static void msg_puts_printf(const char *str, const ptrdiff_t maxlen)
         *p++ = '\r';
       }
       memcpy(p, s, (size_t)len);
-      *(p + len) = '\0';
+      *(p + len) = NUL;
       if (info_message) {
         printf("%s", buf);
       } else {
diff --git a/src/nvim/ops.c b/src/nvim/ops.c
index 74c6e83495..1448896146 100644
--- a/src/nvim/ops.c
+++ b/src/nvim/ops.c
@@ -4725,7 +4725,7 @@ bool do_addsub(int op_type, pos_T *pos, int length, linenr_T Prenum1)
         buf2[i++] = ((n >> --bits) & 0x1) ? '1' : '0';
       }
 
-      buf2[i] = '\0';
+      buf2[i] = NUL;
     } else if (pre == 0) {
       vim_snprintf(buf2, ARRAY_SIZE(buf2), "%" PRIu64, (uint64_t)n);
     } else if (pre == '0') {
diff --git a/src/nvim/quickfix.c b/src/nvim/quickfix.c
index e1d35ab9d5..be2f41da14 100644
--- a/src/nvim/quickfix.c
+++ b/src/nvim/quickfix.c
@@ -724,7 +724,7 @@ static int qf_get_next_str_line(qfstate_T *state)
     state->linelen = len;
   }
   memcpy(state->linebuf, p_str, state->linelen);
-  state->linebuf[state->linelen] = '\0';
+  state->linebuf[state->linelen] = NUL;
 
   // Increment using len in order to discard the rest of the line if it
   // exceeds LINE_MAXLEN.
diff --git a/src/nvim/regexp.c b/src/nvim/regexp.c
index b743664b69..2ff4dbee70 100644
--- a/src/nvim/regexp.c
+++ b/src/nvim/regexp.c
@@ -11495,7 +11495,7 @@ static void nfa_print_state(FILE *debugf, nfa_state_T *state)
   garray_T indent;
 
   ga_init(&indent, 1, 64);
-  ga_append(&indent, '\0');
+  ga_append(&indent, NUL);
   nfa_print_state2(debugf, state, &indent);
   ga_clear(&indent);
 }
@@ -14801,7 +14801,7 @@ static int nfa_regmatch(nfa_regprog_T *prog, nfa_state_T *start, regsubs_T *subm
       }
 
       case NFA_ANY:
-        // Any char except '\0', (end of input) does not match.
+        // Any char except NUL, (end of input) does not match.
         if (curc > 0) {
           add_state = t->state->out;
           add_off = clen;
diff --git a/src/nvim/sha256.c b/src/nvim/sha256.c
index d49224a987..5e0aac3f69 100644
--- a/src/nvim/sha256.c
+++ b/src/nvim/sha256.c
@@ -15,6 +15,7 @@
 #include <stdio.h>
 #include <string.h>
 
+#include "nvim/ascii_defs.h"
 #include "nvim/memory.h"
 #include "nvim/sha256.h"
 
@@ -279,7 +280,7 @@ const char *sha256_bytes(const uint8_t *restrict buf,  size_t buf_len, const uin
   for (size_t j = 0; j < SHA256_SUM_SIZE; j++) {
     snprintf(hexit + j * SHA_STEP, SHA_STEP + 1, "%02x", sha256sum[j]);
   }
-  hexit[sizeof(hexit) - 1] = '\0';
+  hexit[sizeof(hexit) - 1] = NUL;
   return hexit;
 }
 
@@ -340,7 +341,7 @@ bool sha256_self_test(void)
 
     if (memcmp(output, sha_self_test_vector[i], SHA256_BUFFER_SIZE) != 0) {
       failures = true;
-      output[sizeof(output) - 1] = '\0';
+      output[sizeof(output) - 1] = NUL;
 
       // printf("sha256_self_test %d failed %s\n", i, output);
     }
diff --git a/src/nvim/sign.c b/src/nvim/sign.c
index be207f58b0..496913f9bf 100644
--- a/src/nvim/sign.c
+++ b/src/nvim/sign.c
@@ -292,8 +292,8 @@ static void sign_list_placed(buf_T *rbuf, char *group)
         qsort((void *)&kv_A(signs, 0), kv_size(signs), sizeof(MTKey), sign_row_cmp);
 
         for (size_t i = 0; i < kv_size(signs); i++) {
-          namebuf[0] = '\0';
-          groupbuf[0] = '\0';
+          namebuf[0] = NUL;
+          groupbuf[0] = NUL;
           MTKey mark = kv_A(signs, i);
 
           DecorSignHighlight *sh = decor_find_sign(mt_decor(mark));
@@ -498,7 +498,7 @@ static void sign_list_by_name(char *name)
 static int sign_place(uint32_t *id, char *group, char *name, buf_T *buf, linenr_T lnum, int prio)
 {
   // Check for reserved character '*' in group name
-  if (group != NULL && (*group == '*' || *group == '\0')) {
+  if (group != NULL && (*group == '*' || *group == NUL)) {
     return FAIL;
   }
 
@@ -649,14 +649,14 @@ static void sign_place_cmd(buf_T *buf, linenr_T lnum, char *name, int id, char *
     //   :sign place
     //   :sign place group={group}
     //   :sign place group=*
-    if (lnum >= 0 || name != NULL || (group != NULL && *group == '\0')) {
+    if (lnum >= 0 || name != NULL || (group != NULL && *group == NUL)) {
       emsg(_(e_invarg));
     } else {
       sign_list_placed(buf, group);
     }
   } else {
     // Place a new sign
-    if (name == NULL || buf == NULL || (group != NULL && *group == '\0')) {
+    if (name == NULL || buf == NULL || (group != NULL && *group == NUL)) {
       emsg(_(e_invarg));
       return;
     }
@@ -668,7 +668,7 @@ static void sign_place_cmd(buf_T *buf, linenr_T lnum, char *name, int id, char *
 /// ":sign unplace" command
 static void sign_unplace_cmd(buf_T *buf, linenr_T lnum, const char *name, int id, char *group)
 {
-  if (lnum >= 0 || name != NULL || (group != NULL && *group == '\0')) {
+  if (lnum >= 0 || name != NULL || (group != NULL && *group == NUL)) {
     emsg(_(e_invarg));
     return;
   }
@@ -695,7 +695,7 @@ static void sign_jump_cmd(buf_T *buf, linenr_T lnum, const char *name, int id, c
     return;
   }
 
-  if (buf == NULL || (group != NULL && *group == '\0') || lnum >= 0 || name != NULL) {
+  if (buf == NULL || (group != NULL && *group == NUL) || lnum >= 0 || name != NULL) {
     // File or buffer is not specified or an empty group is used
     // or a line number or a sign name is specified.
     emsg(_(e_invarg));
@@ -1316,7 +1316,7 @@ void f_sign_getplaced(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
         if (group == NULL) {
           return;
         }
-        if (*group == '\0') {  // empty string means global group
+        if (*group == NUL) {  // empty string means global group
           group = NULL;
         }
       }
diff --git a/src/nvim/strings.c b/src/nvim/strings.c
index 329b66cea1..bf7af40a38 100644
--- a/src/nvim/strings.c
+++ b/src/nvim/strings.c
@@ -333,7 +333,7 @@ void vim_strcpy_up(char *restrict dst, const char *restrict src)
   while ((c = (uint8_t)(*src++)) != NUL) {
     *dst++ = (char)(uint8_t)(c < 'a' || c > 'z' ? c : c - 0x20);
   }
-  *dst = '\0';
+  *dst = NUL;
 }
 
 // strncpy (NUL-terminated) plus vim_strup.
@@ -344,7 +344,7 @@ void vim_strncpy_up(char *restrict dst, const char *restrict src, size_t n)
   while (n-- && (c = (uint8_t)(*src++)) != NUL) {
     *dst++ = (char)(uint8_t)(c < 'a' || c > 'z' ? c : c - 0x20);
   }
-  *dst = '\0';
+  *dst = NUL;
 }
 
 // memcpy (does not NUL-terminate) plus vim_strup.
@@ -794,10 +794,10 @@ static int format_typeof(const char *type)
   FUNC_ATTR_NONNULL_ALL
 {
   // allowed values: \0, h, l, L
-  char length_modifier = '\0';
+  char length_modifier = NUL;
 
   // current conversion specifier character
-  char fmt_spec = '\0';
+  char fmt_spec = NUL;
 
   // parse 'h', 'l', 'll' and 'z' length modifiers
   if (*type == 'h' || *type == 'l' || *type == 'z') {
@@ -865,7 +865,7 @@ static int format_typeof(const char *type)
     } else if (fmt_spec == 'd') {
       // signed
       switch (length_modifier) {
-      case '\0':
+      case NUL:
       case 'h':
         // char and short arguments are passed as int.
         return TYPE_INT;
@@ -879,7 +879,7 @@ static int format_typeof(const char *type)
     } else {
       // unsigned
       switch (length_modifier) {
-      case '\0':
+      case NUL:
       case 'h':
         return TYPE_UNSIGNEDINT;
       case 'l':
@@ -1050,7 +1050,7 @@ static int parse_fmt_types(const char ***ap_types, int *num_posarg, const char *
       p += n;
     } else {
       // allowed values: \0, h, l, L
-      char length_modifier = '\0';
+      char length_modifier = NUL;
 
       // variable for positional arg
       int pos_arg = -1;
@@ -1441,7 +1441,7 @@ int vim_vsnprintf_typval(char *str, size_t str_m, const char *fmt, va_list ap_st
       int space_for_positive = 1;
 
       // allowed values: \0, h, l, 2 (for ll), z, L
-      char length_modifier = '\0';
+      char length_modifier = NUL;
 
       // temporary buffer for simple numeric->string conversion
 #define TMP_LEN 350    // 1e308 seems reasonable as the maximum printable
@@ -1466,7 +1466,7 @@ int vim_vsnprintf_typval(char *str, size_t str_m, const char *fmt, va_list ap_st
       size_t zero_padding_insertion_ind = 0;
 
       // current conversion specifier character
-      char fmt_spec = '\0';
+      char fmt_spec = NUL;
 
       // buffer for 's' and 'S' specs
       char *tofree = NULL;
@@ -1669,7 +1669,7 @@ int vim_vsnprintf_typval(char *str, size_t str_m, const char *fmt, va_list ap_st
       case 'o':
       case 'x':
       case 'X':
-        if (tvs && length_modifier == '\0') {
+        if (tvs && length_modifier == NUL) {
           length_modifier = 'L';
         }
       }
@@ -1790,7 +1790,7 @@ int vim_vsnprintf_typval(char *str, size_t str_m, const char *fmt, va_list ap_st
         } else if (fmt_spec == 'd') {
           // signed
           switch (length_modifier) {
-          case '\0':
+          case NUL:
             arg = (tvs
                    ? (int)tv_nr(tvs, &arg_idx)
                    : (skip_to_arg(ap_types, ap_start, &ap, &arg_idx,
@@ -1836,7 +1836,7 @@ int vim_vsnprintf_typval(char *str, size_t str_m, const char *fmt, va_list ap_st
         } else {
           // unsigned
           switch (length_modifier) {
-          case '\0':
+          case NUL:
             uarg = (tvs
                     ? (unsigned)tv_nr(tvs, &arg_idx)
                     : (skip_to_arg(ap_types, ap_start, &ap, &arg_idx,
@@ -2223,7 +2223,7 @@ int vim_vsnprintf_typval(char *str, size_t str_m, const char *fmt, va_list ap_st
   if (str_m > 0) {
     // make sure the string is nul-terminated even at the expense of
     // overwriting the last character (shouldn't happen, but just in case)
-    str[str_l <= str_m - 1 ? str_l : str_m - 1] = '\0';
+    str[str_l <= str_m - 1 ? str_l : str_m - 1] = NUL;
   }
 
   if (tvs != NULL
diff --git a/src/nvim/terminal.c b/src/nvim/terminal.c
index 2b05a8047e..2738eb874d 100644
--- a/src/nvim/terminal.c
+++ b/src/nvim/terminal.c
@@ -845,7 +845,7 @@ void terminal_paste(int count, char **y_array, size_t y_size)
       }
       char *dst = buff;
       char *src = y_array[j];
-      while (*src != '\0') {
+      while (*src != NUL) {
         len = (size_t)utf_ptr2len(src);
         int c = utf_ptr2char(src);
         if (!is_filter_char(c)) {
diff --git a/src/nvim/usercmd.c b/src/nvim/usercmd.c
index e3d9dc5f54..79f897f020 100644
--- a/src/nvim/usercmd.c
+++ b/src/nvim/usercmd.c
@@ -580,7 +580,7 @@ static void uc_list(char *name, size_t name_len)
         IObuff[len++] = ' ';
       } while ((int64_t)len < 25 - over);
 
-      IObuff[len] = '\0';
+      IObuff[len] = NUL;
       msg_outtrans(IObuff, 0);
 
       if (cmd->uc_luaref != LUA_NOREF) {
@@ -831,7 +831,7 @@ invalid_count:
       }
     } else {
       char ch = attr[len];
-      attr[len] = '\0';
+      attr[len] = NUL;
       semsg(_("E181: Invalid attribute: %s"), attr);
       attr[len] = ch;
       return FAIL;
@@ -1364,7 +1364,7 @@ size_t uc_mods(char *buf, const cmdmod_T *cmod, bool quote)
     if (quote) {
       *buf++ = '"';
     }
-    *buf = '\0';
+    *buf = NUL;
   }
 
   // the modifiers that are simple flags