xstrdup, xtrndup: allow NULL argument

Accept NULL argument in xstrdup and xtrndup functions to allow use
of "xstrdup(str)" instead of "str ? xstrdup(str) : NULL".

* xmalloc.c (xstrdup, xstrndup): Handle NULL argument.
* xmalloc.h: Add comment regarding this deviation from the behaviour
of the POSIX counterparts of these functions.

1 files changed, 6 insertions, 0 deletions

diff --git a/xmalloc.c b/xmalloc.c
index 45ff57b15..c2c50f8c6 100644
--- a/xmalloc.c
+++ b/xmalloc.c
@@ -91,6 +91,9 @@ xreallocarray(void *ptr, size_t nmemb, size_t size)
 char *
 xstrdup(const char *str)
 {
+	if (!str)
+		return NULL;
+
 	char *p = strdup(str);
 
 	if (!p)
@@ -104,6 +107,9 @@ xstrndup(const char *str, size_t n)
 {
 	char *p;
 
+	if (!str)
+		return NULL;
+
 #ifdef HAVE_STRNDUP
 	p = strndup(str, n);
 #else