terminology: call them null-terminated strings

Updated terminology in docs, comments and phrases to refer to C strings
as "null-terminated". Done to unify with how most other C oriented docs
refer of them and what users in general seem to prefer (based on a
single highly unscientific poll on twitter).

Reported-by: coinhubs on github
Fixes #5598
Closes #5608

lib/cookie.c

@@ -755,7 +755,7 @@ Curl_cookie_add(struct Curl_easy *data,
         co->path = malloc(pathlen + 1); /* one extra for the zero byte */
         if(co->path) {
           memcpy(co->path, path, pathlen);
-          co->path[pathlen] = 0; /* zero terminate */
+          co->path[pathlen] = 0; /* null-terminate */
           co->spath = sanitize_cookie_path(co->path);
           if(!co->spath)
             badcookie = TRUE; /* out of memory bad */

lib/dotdot.c

@@ -5,7 +5,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2019, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2020, Daniel Stenberg, <daniel@haxx.se>, et al.
  *
  * This software is licensed as described in the file COPYING, which
  * you should have received as part of this distribution. The terms
@@ -39,7 +39,7 @@
  * Curl_dedotdotify()
  * @unittest: 1395
  *
- * This function gets a zero-terminated path with dot and dotdot sequences
+ * This function gets a null-terminated path with dot and dotdot sequences
  * passed in and strips them off according to the rules in RFC 3986 section
  * 5.2.4.
  *
@@ -62,7 +62,7 @@ char *Curl_dedotdotify(const char *input)
   if(!out)
     return NULL; /* out of memory */
 
-  *out = 0; /* zero terminates, for inputs like "./" */
+  *out = 0; /* null-terminates, for inputs like "./" */
 
   /* get a cloned copy of the input */
   clone = strdup(input);
@@ -129,7 +129,7 @@ char *Curl_dedotdotify(const char *input)
         if(*outptr == '/')
           break;
       }
-      *outptr = 0; /* zero-terminate where it stops */
+      *outptr = 0; /* null-terminate where it stops */
     }
     else if(!strcmp("/..", clone)) {
       clone[2]='/';
@@ -141,7 +141,7 @@ char *Curl_dedotdotify(const char *input)
         if(*outptr == '/')
           break;
       }
-      *outptr = 0; /* zero-terminate where it stops */
+      *outptr = 0; /* null-terminate where it stops */
     }
 
     /*  D.  if the input buffer consists only of "." or "..", then remove

lib/dynbuf.c

@@ -161,7 +161,7 @@ CURLcode Curl_dyn_addn(struct dynbuf *s, const void *mem, size_t len)
 }
 
 /*
- * Append a zero terminated string at the end.
+ * Append a null-terminated string at the end.
  */
 CURLcode Curl_dyn_add(struct dynbuf *s, const char *str)
 {

lib/dynbuf.h

@@ -23,7 +23,7 @@
  ***************************************************************************/
 
 struct dynbuf {
-  char *bufr;    /* point to a zero terminated allocated buffer */
+  char *bufr;    /* point to a null-terminated allocated buffer */
   size_t leng;   /* number of bytes *EXCLUDING* the zero terminator */
   size_t allc;   /* size of the current allocation */
   size_t toobig; /* size limit for the buffer */

lib/formdata.c

@@ -602,7 +602,7 @@ CURLFORMcode FormAdd(struct curl_httppost **httppost,
         /* Note that there's small risk that form->name is NULL here if the
            app passed in a bad combo, so we better check for that first. */
         if(form->name) {
-          /* copy name (without strdup; possibly not nul-terminated) */
+          /* copy name (without strdup; possibly not null-terminated) */
           form->name = Curl_memdup(form->name, form->namelength?
                                    form->namelength:
                                    strlen(form->name) + 1);
@@ -771,7 +771,7 @@ void curl_formfree(struct curl_httppost *form)
 }
 
 
-/* Set mime part name, taking care of non nul-terminated name string. */
+/* Set mime part name, taking care of non null-terminated name string. */
 static CURLcode setname(curl_mimepart *part, const char *name, size_t len)
 {
   char *zname;

lib/ftp.c

@@ -2827,7 +2827,7 @@ static CURLcode ftp_statemach_act(struct connectdata *conn)
             store++;
             ptr++;
           }
-          *store = '\0'; /* zero terminate */
+          *store = '\0'; /* null-terminate */
         }
         if(entry_extracted) {
           /* If the path name does not look like an absolute path (i.e.: it
@@ -2891,7 +2891,7 @@ static CURLcode ftp_statemach_act(struct connectdata *conn)
           ptr++;
         for(store = os; *ptr && *ptr != ' ';)
           *store++ = *ptr++;
-        *store = '\0'; /* zero terminate */
+        *store = '\0'; /* null-terminate */
 
         /* Check for special servers here. */
 

lib/http.c

@@ -270,7 +270,7 @@ char *Curl_copy_header_value(const char *header)
     return NULL;
 
   memcpy(value, start, len);
-  value[len] = 0; /* zero terminate */
+  value[len] = 0; /* null-terminate */
 
   return value;
 }

lib/mime.c

@@ -1419,7 +1419,7 @@ CURLcode curl_mime_data(curl_mimepart *part,
 
     if(datasize)
       memcpy(part->data, data, datasize);
-    part->data[datasize] = '\0';    /* Set a nul terminator as sentinel. */
+    part->data[datasize] = '\0';    /* Set a null terminator as sentinel. */
 
     part->readfunc = mime_mem_read;
     part->seekfunc = mime_mem_seek;

lib/pingpong.c

@@ -384,10 +384,10 @@ CURLcode Curl_pp_readresp(curl_socket_t sockfd,
 
           if(pp->endofresp(conn, pp->linestart_resp, perline, code)) {
             /* This is the end of the last line, copy the last line to the
-               start of the buffer and zero terminate, for old times sake */
+               start of the buffer and null-terminate, for old times sake */
             size_t n = ptr - pp->linestart_resp;
             memmove(buf, pp->linestart_resp, n);
-            buf[n] = 0; /* zero terminate */
+            buf[n] = 0; /* null-terminate */
             keepon = FALSE;
             pp->linestart_resp = ptr + 1; /* advance pointer */
             i++; /* skip this before getting out */

lib/strerror.c

@@ -795,7 +795,7 @@ const char *Curl_strerror(int err, char *buf, size_t buflen)
 
 #endif /* end of not Windows */
 
-  buf[max] = '\0'; /* make sure the string is zero terminated */
+  buf[max] = '\0'; /* make sure the string is null-terminated */
 
   /* strip trailing '\r\n' or '\n'. */
   p = strrchr(buf, '\n');

lib/strtok.c

@@ -5,7 +5,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2019, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2020, Daniel Stenberg, <daniel@haxx.se>, et al.
  *
  * This software is licensed as described in the file COPYING, which
  * you should have received as part of this distribution. The terms
@@ -52,7 +52,7 @@ Curl_strtok_r(char *ptr, const char *sep, char **end)
 
     if(**end) {
       /* the end is not a null byte */
-      **end = '\0';  /* zero terminate it! */
+      **end = '\0';  /* null-terminate it! */
       ++*end;        /* advance the last pointer to beyond the null byte */
     }
 

lib/urlapi.c

@@ -225,7 +225,7 @@ static void strcpy_url(char *output, const char *url, bool relative)
       break;
     }
   }
-  *optr = 0; /* zero terminate output buffer */
+  *optr = 0; /* null-terminate output buffer */
 
 }
 
@@ -584,7 +584,7 @@ static CURLUcode junkscan(const char *part)
       0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
       0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f,
       0x7f,
-      0x00 /* zero terminate */
+      0x00 /* null-terminate */
     };
     size_t n = strlen(part);
     size_t nfine = strcspn(part, badbytes);
@@ -1398,7 +1398,7 @@ CURLUcode curl_url_set(CURLU *u, CURLUPart what,
         i = (const unsigned char *)part;
         for(o = enc; *i; ++o, ++i)
           *o = (*i == ' ') ? '+' : *i;
-        *o = 0; /* zero terminate */
+        *o = 0; /* null-terminate */
         part = strdup(enc);
         if(!part) {
           free(enc);
@@ -1422,7 +1422,7 @@ CURLUcode curl_url_set(CURLU *u, CURLUPart what,
           o += 3;
         }
       }
-      *o = 0; /* zero terminate */
+      *o = 0; /* null-terminate */
       newp = enc;
       if(free_part)
         free((char *)part);

lib/urldata.h

@@ -1564,7 +1564,7 @@ enum dupstring {
   STRING_DNS_LOCAL_IP4,
   STRING_DNS_LOCAL_IP6,
 
-  /* -- end of zero-terminated strings -- */
+  /* -- end of null-terminated strings -- */
 
   STRING_LASTZEROTERMINATED,
 

lib/vtls/openssl.c

@@ -1636,7 +1636,7 @@ static CURLcode verifyhost(struct connectdata *conn, X509 *server_cert)
              type itself: for example for an IA5String the data will be ASCII"
 
              It has been however verified that in 0.9.6 and 0.9.7, IA5String
-             is always zero-terminated.
+             is always null-terminated.
           */
           if((altlen == strlen(altptr)) &&
              /* if this isn't true, there was an embedded zero in the name

lib/vtls/vtls.c

@@ -706,7 +706,7 @@ CURLcode Curl_ssl_init_certinfo(struct Curl_easy *data, int num)
 }
 
 /*
- * 'value' is NOT a zero terminated string
+ * 'value' is NOT a null-terminated string
  */
 CURLcode Curl_ssl_push_certinfo_len(struct Curl_easy *data,
                                     int certnum,
@@ -728,10 +728,10 @@ CURLcode Curl_ssl_push_certinfo_len(struct Curl_easy *data,
   /* sprintf the label and colon */
   msnprintf(output, outlen, "%s:", label);
 
-  /* memcpy the value (it might not be zero terminated) */
+  /* memcpy the value (it might not be null-terminated) */
   memcpy(&output[labellen + 1], value, valuelen);
 
-  /* zero terminate the output */
+  /* null-terminate the output */
   output[labellen + 1 + valuelen] = 0;
 
   nl = Curl_slist_append_nodup(ci->certinfo[certnum], output);