.I c
in string
.IR s ,
-or
-.L 0
-if
+or nil if
.I c
does not occur in the string.
The null byte terminating a string is considered to
.I s1
of any byte from string
.IR s2 ,
-.L 0
-if no byte from
+nil if no byte from
.I s2
exists in
.IR s1 .
between separate calls; subsequent calls,
signified by
.I s1
-being
-.LR 0 ,
-will work through the string
+being nil, will work through the string
.I s1
immediately following that token.
The separator string
may be different from call to call.
When no token remains in
.IR s1 ,
-.L 0
-is returned.
+nil is returned.
.PP
.I Strdup
returns a pointer to a distinct copy of the null-terminated string
.I s
in space obtained from
.IR malloc (2)
-or
-.L 0
-if no space can be obtained.
+or nil if no space can be obtained.
.PP
.I Strstr
returns a pointer to the first occurrence of
.I s2
as a substring of
.IR s1 ,
-or 0 if there is none.
+or nil if there is none.
If
.I s2
is the null string,