curl_slist_append.3: clarify a NULL input creates a new list

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.\" * Copyright (C) 1998 - 2016, Daniel Stenberg, <daniel@haxx.se>, et al.

.\" * Copyright (C) 1998 - 2017, Daniel Stenberg, <daniel@haxx.se>, et al.

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.\" * This software is licensed as described in the file COPYING, which

.\" * you should have received as part of this distribution. The terms

.BI "const char * "string ");"

.ad

.SH DESCRIPTION

curl_slist_append() appends a specified string to a linked list of

strings. The existing \fIlist\fP should be passed as the first argument while

the new list is returned from this function. The specified \fIstring\fP has

been appended when this function returns. curl_slist_append() copies the

string.

\fIcurl_slist_append(3)\fP appends a string to a linked list of strings. The

existing \fBlist\fP should be passed as the first argument and the new list is

returned from this function. Pass in NULL in the \fBlist\fP argument to create

a new list. The specified \fBstring\fP has been appended when this function

returns. \fIcurl_slist_append(3)\fP copies the string.

The list should be freed again (after usage) with

\fIcurl_slist_free_all(3)\fP.

pointer is returned.

.SH EXAMPLE

.nf

 CURL handle;

CURL *handle;

struct curl_slist *slist=NULL;

slist = curl_slist_append(slist, "pragma:");